mercury contamination within terrestrial ecosystems in new ... · lane, and j. franklin. 2011....

Mercury Contamination within Terrestrial Ecosystems in New England and Mid-Atlantic States:

Profiles of Soil, Invertebrates, Songbirds, and Bats

Biodiversity Research Institute

Mercury Contamination within Terrestrial Ecosystems

in New England and Mid-Atlantic States:

Profiles of Soil, Invertebrates, Songbirds, and Bats

SUBMITTED TO:

Dr. Tim Tear

The Nature Conservancy – Eastern New York Chapter

195 New Karner Road

Albany, NY 12205

SUBMITTED BY:


652 Main St.

Gorham, Maine, USA 04038

(207-839-7600)

FINAL DRAFT SUBMITTED ON:

27 January 2012


Biodiversity Research Institute (BRI) is a 501(c)3 nonprofit organization located in

Gorham, Maine. The mission of Biodiversity Research Institute is to assess ecological

health through collaborative research, and to use scientific findings to advance

environmental awareness and inform decision makers.

To obtain copies of this report contact:


19 Flaggy Meadow Road

Gorham, ME 04038

(207) 839-7600

www.briloon.org

COVER ILLUSTRATION: Shearon Murphy

SUGGESTED CITATION: Osborne, C. E, D. C. Evers, M. Duron, N. Schoch, D. Yates, D. Buck, O. P.

Lane, and J. Franklin. 2011. Mercury Contamination within Terrestrial Ecosystems

in New England and Mid-Atlantic States: Profiles of Soil, Invertebrates, Songbirds, and Bats.

Report BRI 2011-09. Submitted to The Nature Conservancy – Eastern New York Chapter.

Biodiversity Research Institute, Gorham, Maine.


Table of Contents

LIST OF FIGURES ................................................................................................................................................... 5

LIST OF TABLES..................................................................................................................................................... 9

1.0 EXECUTIVE SUMMARY ............................................................................................................................. 10

2.0 INTRODUCTION .......................................................................................................................................... 11

3.0 SOILS ................................................................................................................................................................ 15

3.1 STUDY AREA .................................................................................................................................. 15 3.2 METHODS ....................................................................................................................................... 15 3.3 RESULTS AND DISCUSSION ..................................................................................................... 16

3.3.1 MERCURY LEVELS IN SOIL ............................................................................................ 16 3.3.2.1 SOIL MOISTURE .............................................................................................................. 17 3.3.2.2 SOIL CHEMISTRY ........................................................................................................... 18

3.4 CONCLUSION ................................................................................................................................. 21

4.0 INVERTEBRATES ........................................................................................................................................ 22

4.1 STUDY AREA ................................................................................................................................... 22 4.2 METHODS ........................................................................................................................................ 22

4.2.1 STATISTICAL ANALYSIS ................................................................................................. 23 4.3 RESULTS AND DISCUSSION ...................................................................................................... 23

4.3.1 SAMPLING EFFORT ........................................................................................................... 23 4.3.2. REGIONAL AND SPECIES MERCURY EXPOSURE.................................................. 23

4.4 CONCLUSION .................................................................................................................................. 28

5.0 SONGBIRDS ................................................................................................................................................... 29

5.1 STUDY AREA .................................................................................................................................... 29 5.2 METHODS ......................................................................................................................................... 29

5.2.1 STATISTICAL ANALYSIS ................................................................................................. 29 5.3 RESULTS AND DISCUSSION ........................................................................................................ 31

5.3.1 SAMPLING EFFORT ........................................................................................................... 31 5.3.2 REGIONAL AND SPECIES MERCURY EXPOSURE .................................................. 31 5.3.2.1 CASE STUDY #3 - SALTMARSH SPARROW .......................................................... 34 5.3.2.2 CASE STUDY #4 - RUSTY BLACKBIRD ................................................................... 35 5.3.3 MERCURY EXPOSURE BY FORAGING GUILD .......................................................... 37 5.3.3.1 CASE STUDY # 5 - RELATIONSHIP BETWEEN SOIL Hg AND A GROUND-FORAGING SONGBIRD: THE WOOD THRUSH ................................................................... 42 5.3.4 MERCURY EXPOSURE BY FAMILY .............................................................................. 50 5.3.4.1 SONGBIRD CASE STUDY #6 - BICKNELL’S THRUSH ........................................ 52 5.3.5 BLOOD MERCURY CONCENTRATIONS AND REPRODUCTIVE SUCCESS ..... 54 5.3.5.1 SONGBIRD CASE STUDY # 7 - CAROLINA WREN .............................................. 55

5.4 CONCLUSIONS ................................................................................................................................ 57

6.0 BATS ................................................................................................................................................................. 58


6.1 STUDY AREA .................................................................................................................................... 58 6.2 METHODS ......................................................................................................................................... 58 6.3 RESULTS AND DISCUSSION ....................................................................................................... 58

6.3.1 SPECIES MERCURY EXPOSURE .................................................................................... 58 6.3.2 REGIONAL MERCURY EXPOSURE ............................................................................... 61 6.3.4 MERCURY EXPOSURE BY AGE AND SEX................................................................... 67

6.4 CONCLUSIONS ................................................................................................................................ 68

7.0 POLICY AND MANAGEMENT RECOMMENDATIONS .................................................................... 70

8.0 ACKNOWLEDGEMENTS ........................................................................................................................... 72

9.0 LITERATURE CITED .................................................................................................................................. 74

10.0 APPENDIX A – COMMON AND LATIN NAMES OF SONGBIRDS SAMPLED FOR BLOOD HG

CONCENTRATIONS. .......................................................................................................................................... 89

11.0 APPENDIX B – SONGBIRD MERCURY EXPOSURE BY SPECIES .............................................. 92

12.0 APPENDIX C – SONGBIRD MERCURY EXPOSURE BY FAMILY ............................................... 96

LIST OF FIGURES Figure 1. Study area map of soil sampling locations. .......................................................................... 15 Figure 2. Mean plus standard deviation and maximum level detected of Hg in soil sampled in PA, VA, and four regions of NY. ................................................................................................................ 18 Figure 4. Relationship between pH and Hg concentrations in organic and mineral soil layers in samples (N = 31) collected at IES in Millbrook, NY ......................................................................... 19 Figure 5. Relationship between pH and exchangeable calcium (Ca) concentrations in organic and mineral soil layers in samples (N = 42) collected at IES in Millbrook, NY .......... 19 Figure 6. Relationship between pH and exchangeable potassium (K) in the organic and mineral soil layers in samples (N = 42) collected at IES in Millbrook, NY ................................... 20 Figure 7. Relationship between pH and exchangeable magnesium (Mg) in the organic and mineral soil layers in samples (N = 42) collected at IES in Millbrook, NY. .................................. 21 Figure 8. Invertebrate sampling locations in New England and the Mid-Atlantic States, 2005 to 2008, and 2010. ................................................................................................................................. 22 Figure 9. Mean plus standard deviation and maximum levels detected of MeHg concentrations in invertebrate orders sampled in New England and Mid-Atlantic States, 2005 to 2010. ....................................................................................................................................................... 24


Figure 10. Regional means plus standard deviation and maximum levels detected of MeHg concentrations in Araneae species sampled in New England and Mid-Atlantic States, 2005 to 2010. ................................................................................................................................................................ 24 Figure 11. Map of Lake George, NY showing the location of Dome Island .................................. 26 Figure 12. Study area map of songbird sampling locations.............................................................. 30 Figure 13. Regional means plus standard deviations and maximum levels detected of blood Hg levels (ppm) in songbirds sampled in New England and Mid-Atlantic States, 1999 to 2007. ....................................................................................................................................................................... 31 Figure 14. Mean plus standard deviation and maximum level detected of blood Hg concentrations in songbirds sampled in Southwest VA, 2005 to 2007. ....................................... 33

Figure 15. Mean plus standard deviation and maximum level detected of blood Hg concentrations in songbirds sampled in Adirondack Mts, NY region, 2006 and 2007. .......... 33 Figure 16. Mean plus standard deviation and maximum level detected of blood Hg in Saltmarsh Sparrows sampled in coastal New England and Long Island, NY, 2000 to 2007. 35 Figure 17. Regional mean plus standard deviation and maximum level detected of blood Hg concentrations detected in Rusty Blackbirds in New England, 2007 to 2010. .......................... 37 Figure 18. Mean blood Hg level (ppm) by songbird foraging guild as defined by De Graaf et al. (1985). .............................................................................................................................................................. 40 Figure 19. Mean plus standard deviation and maximum level detected of blood Hg concentrations in “omnivore ground” foraging guild species sampled in New England and Mid-Atlantic States, 2000 to 2007. .............................................................................................................. 41 Figure 20. Mean plus standard deviation and maximum level detected of blood Hg concentrations in “insectivore ground” foraging guild species sampled in New England and the Mid-Atlantic States, 2004 to 2010. ...................................................................................................... 41 Figure 21. Relationship between the amount of exchangeable calcium in the organic and mineral soil layer and Wood Thrush (N = 6) blood Hg concentrations. ....................................... 43 Figure 22. The relationship between the amount of exchangeable Ca in the organic and mineral soil layers and blood Hg concentrations of Wood Thrushes (N = 6) ............................ 43 Figure 23. Mean plus standard deviation and maximum level detected of blood Hg concentrations among “insectivore air” foraging guild species sampled in New England and Mid-Atlantic States, 2005 to 2007. .............................................................................................................. 45


Figure 24. Mean plus standard deviation and maximum level detected of blood Hg concentrations in “omnivore ground/lower-canopy” foraging guild species sampled in New England and Mid-Atlantic States, 1999 to 2007. .................................................................................... 45 Figure 25. Mean plus standard deviation and maximum level detected of blood Hg concentrations in “insectivore upper-canopy” foraging guild species sampled in New England and the Mid-Atlantic States, 1999 to 2010. ............................................................................ 46 Figure 26. Mean plus standard deviation and maximum level detected of blood Hg concentrations in Louisiana Waterthrush and Northern Waterthrush sampled in New England and Mid-Atlantic States, 2005 to 2007. .................................................................................... 48 Figure 27. Mean plus standard deviation and maximum level detected of blood Hg concentrations in “insectivore lower-canopy” foraging guild species sampled in New England and Mid-Atlantic States, 2004 to 2007. .................................................................................... 49 Figure 28. Mean plus standard deviation and maximum level detected of blood Hg concentrations among songbird families sampled in New England and Mid-Atlantic States, 1999 to 2010. ....................................................................................................................................................... 50 Figure 29. Mean plus standard deviation and maximum level detected of blood Hg concentrations in Tyrannidae species sampled in New England and Mid-Atlantic States, 2005 to 2007. ....................................................................................................................................................... 51 Figure 30. Mean blood Hg concentration in Turdidae family species sampled in New England and Mid-Atlantic States, 1999 – 2008. ..................................................................................... 53 Figure 31. Regional means plus standard deviations and maximum levels detected of blood Hg concentrations Bicknell’s Thrush sampled in New England and New York, 1999 – 2007. ................................................................................................................................................................................... 54 Figure 32. Songbird species sampled in New England and the Mid-Atlantic States between 1999 and 2010 with individuals whose blood Hg (ppm, ww) concentrations put them at risk of reduced nesting success. ................................................................................................................... 56 Figure 33. Study area of bat sampling locations. ................................................................................... 60 Figure 34. Mean plus standard deviation and maximum level detected of fur Hg concentrations in bat species sampled in New England and Mid-Atlantic States, 2006 to 2008. ....................................................................................................................................................................... 61 Figure 35. Regional mean fur Hg concentrations in bats sampled in New England and Mid-Atlantic States, 2006 to 2008. ....................................................................................................................... 62 Figure 36. Mean and maximum level detected of fur Hg (ppm) in bats sampled near Little River, Rockingham County in Southeastern NH, 2008. ....................................................................... 63


Figure 37. Regional mean fur Hg concentrations in Big Brown Bats sampled in New England and Mid-Atantic States, 2006 to 2008 ...................................................................................... 64 Figure 38. Regional mean fur Hg concentrations in Eastern Small-footed Myotis sampled in coastal ME, southern NY, and WV, 2006 to 2008. ............................................................................... 65 Figure 39. Regional mean and maximum levels detected of fur Hg concentrations in Indiana Bats sampled in New York State, 2006 to 2008. .................................................................... 65 Figure 40. Regional means and maximum levels detected of fur Hg in Northern Long-eared Bats sampled in New England and Mid-Atlantic States, 2006 to 2008 ......................................... 65

Figure 41. Regional means and maximum levels detected of fur Hg concentrations in Eastern Pipistrelles sampled in WV and Coastal VA, 2007 and 2008. .......................................... 66 Figure 42. Regional means and maximum levels detected of fur Hg concentrations in Red Bat sampled in New England and Mid-Atlantic States, 2006 to 2008 ........................................... 66 Figure 43. Regional means and maximum levels detected of fur Hg concentrations in Little Brown Bats sampled in New England and Mid-Atlantic States, 2006 to 2008 .......................... 67 Figure 44. Mean fur Hg concentrations among male and female adult and juvenile bats sampled in New England and the Mid-Atlantic States, 2006 to 2008 ........................................... 68 Figure 45. Mean plus standard deviation of blood Hg concentrations in Cardinalidae species. ................................................................................................................................................................... 96 Figure 46. Mean and maximum level detected of blood Hg concentrations in Emberizidae species. ................................................................................................................................................................... 96 Figure 47. Mean and maximum blood Hg concentrations in Hirundinidae species. ............... 97 Figure 48. Mean plus standard deviation and maximum level detected of blood Hg concentrations in Icteridae species. ........................................................................................................... 97 Figure 49. Mean plus standard deviation and maximum level detected of blood Hg concentrations in Paridae species. .............................................................................................................. 98 Figure 50. Mean plus standard deviation and maximum level detected of blood Hg concentrations in Parulidae species. .......................................................................................................... 98 Figure 51. Mean plus standard deviation and maximum level detected of blood Hg concentrations in Sittidae species. .............................................................................................................. 99


Figure 52. Mean plus standard deviation and maximum level detected of blood Hg concentrations in Troglodytidae species. ................................................................................................. 99 Figure 53. Mean plus standard deviation and maximum level detected of blood Hg concentrations in Vireonidae species. ..................................................................................................... 100

LIST OF TABLES Table 1. Carolina Wren blood, feather, and egg Hg effects concentrations associated with MCestimate-modeling reduction in nest success (adapted from Jackson et al. 2011). .......... 56


1.0 EXECUTIVE SUMMARY

Multiple environmental stressors such as acid rain, habitat degradation, and global climate

change, are well established threats to biological diversity in North America. Recently,

compelling investigations into the adverse impacts of mercury on wildlife indicate that

mercury may be another pervasive and invisible risk to ecosystem health. Although great

strides in the reduction of anthropogenically released mercury have been made,

environmental loads continue to be of concern. Not only are new locations of high mercury

concentrations (or biological mercury hotspots) being discovered, but taxa within

foodwebs once thought safe are in danger.

The following synthesis describes a hidden, or invisible, impact of methylmercury

contamination across ecosystems in the northeastern United States— from Virginia to New

York to Maine. We herein document and describe the potential adverse impacts of mercury

to invertivores, such as songbirds and bats. While past investigations have rightly

emphasized adverse impacts to fish-eating wildlife, such as Common Loons (Gavia immer),

Bald Eagles (Haliaeetus leucocephalus), and River Otter (Lontra canadensis), recent findings

by BRI researchers and their colleagues have now established that terrestrial food webs

have great ability to biomagnify methylmercury to levels of conservation concern. This

finding is not restricted to areas with waterborne point sources, such as industrial sites on

rivers, but also reflects exposure in remote habitats through atmospheric deposition.

Research has shown that mercury biomagnification within the invertebrate community,

which comprises the prey base for the species highlighted in this report, is the critical link

to understanding how mercury cycles through terrestrial ecosystems. As food chain length

increases, we see higher levels of mercury in the top-level predators.

We sampled approximately 80 songbird species from many different habitats that had

blood mercury concentrations exceeding the current level of concern. Research has shown

that the risk of methylmercury toxicity varies greatly depending on the physical, chemical,

and biological components of an ecosystem. We found that species inhabiting wetland

ecosystems, such as bog and beaver ponds (e.g., Rusty Blackbird (Euphagus carolinus)) or

estuaries (e.g., Saltmarsh Sparrow (Ammodramus caudacutus)) are at the highest risk for

mercury bioaccumulation. This does not, however, mean that birds in upland ecosystems

are sheltered from mercury contamination; we also found mercury in the blood of species

such as Bicknell’s Thrush (Catharus bicknelli), who live in high elevation forests thought to

be removed from mercury contamination.

Established effect levels remain undefined for bats, however evidence indicates that 10

ppm in the fur of bats correlates with biochemical changes in the brain. Seven out of nine


species of bat sampled in this study had individuals that exceeded this level of concern,

indicating bats bioaccumulate mercury at high levels across many different ecosystems.

Bats are considerably longer lived than most songbirds, making them more likely to build

high levels of mercury over time.

This investigation provides critical information to policy makers regarding the

pervasiveness of environmental mercury pollution in the northeastern United States. The

results from this study indicate that mercury levels in songbirds, bats, and invertebrates

throughout the Northeast are high enough to cause detrimental effects to populations

inhabiting areas prone to bioaccumulation of mercury in the terrestrial food web.

Continued research should focus on the interaction of the multiple environmental stressors

including mercury, climate change, and acid deposition. Modeling the impacts of these

factors will help us better identify biological mercury hotspots and on-the-ground

biomonitoring will allow us to validate the pathway of mercury in the environment through

the food web.

2.0 INTRODUCTION

Air pollution has been linked to adverse effects in wildlife (Lovett et al. 2009). Specifically,

elevated levels of atmospheric sulfur (S), nitrogen (N), and mercury (Hg) deposition in the

Northeastern United States have negatively influenced wildlife populations (Graveland

1990, Hames et al. 2002, Rimmer et al. 2005, Evers et al. 2008). Mercury, in particular, has

been well-studied and observed to “biomagnify”, i.e., increase in concentration, and thus

toxicity, with increasing trophic level within a food web; however, most of the

investigations have been focused on freshwater aquatic ecosystems (Evers et al. 2005,

Chen et al. 2005, Kamman et al. 2005, Pennuto et al. 2005). Despite the recent

documentation of elevated Hg exposure in terrestrial biota, relatively little is known about

pathways for Hg uptake and transfer in upland ecosystems (Cristol et al. 2008, Rimmer et

al. 2010).

Globally, the inventory of mercury in surface soils far exceeds that in the aquatic and

atmospheric compartments (Wiener et al. 2003). The vast majority (947Mmol) of the

estimated total mass of mercury released to the environment in the past century resides in

surface soils, compared to 17 Mmol in the atmosphere and 36 Mmol in the oceans (Wiener

et al. 2003). Consequently, in order to understand mercury cycling in the terrestrial

environment, one must consider the role of soil and what factors influence Hg retention

and release to surrounding watersheds and uptake by biota at the base of the food web.

And then, to truly disentangle mercury’s effects on ecosystem structure and function, it is

important to consider how factors that influence Hg chemistry in the soil profile act in

other ways to affect soil structure and function.


The different chemical forms of Hg in the atmosphere have varying residence times (hours

to months) and transport distances (local to global) (Driscoll et al. 2007, Lovett et al. 2009).

Highly soluble Hg (II) species are quickly stripped from the atmosphere and deposited

locally, whereas aerosol (Hg-p) emissions are transported regionally, and elemental (Hg0)

emissions are transported globally (Keeler et al. 1995, Lindberg and Stratton 1998,

Schroeder and Munthe 1998, Demers et al. 2007). Litterfall and throughfall deliver

different forms of mercury to the forest floor. Gaseous elemental mercury (Hg0) contacting

leaf surfaces is either re-emitted to the atmosphere or taken up by stomata and retained

internally by the leaf tissue until deposited in litterfall (Mosbaek et al. 1988, Demers et al.

2007). Reactive Gaseous Mercury (Hg(II)) and Hg-p are adsorbed to the leaf surface during

dry deposition and may be leached from those surfaces during precipitation events,

contributing to elevated mercury levels in throughfall (Iverfeldt 1991, Kolka et al. 1999,

Rea et al. 2000, 2001, Demers et al. 2007). Additionally, Rimmer et al. (2005) cited

numerous studies that have demonstrated that methylmercury (MeHg),the toxic form of

mercury, is present in both live and recently senesced forest foliage in proportions of

approximately 1% of the total Hg content (e.g., Lee et al. 2000, Schwesig and Matzner 2000,

St. Louis et al. 2001, Ericksen et al. 2003).

The speciation of mercury in most upland soils is probably dominated by divalent mercury

species that are sorbed primarily to organic matter in the humus layer and secondarily to

mineral constituents in the soil (Lindquvist 1991, Kim et al. 1997, Wiener et al. 2003). The

availability of Hg (II) to organisms is determined by its activity in soil solution, which is, in

turn, controlled by both the solid and solution phase characteristics of the soil (Jing et al.

2007). Many environmental factors can interfere with the Hg adsorption-desorption

process, which include: Hg speciation, soil pH, chloride ions, organic matter content, form

and content of soil colloids, and competitive inorganic ions, etc. (Jing et al. 2007).

Therefore, fine, spatial-scale patterns such as local variation in vegetation type (receptor

surface) and microclimate may be important determinants of the watershed-scale capture

of atmospheric mercury (Miller et al. 2005) .

Acid rain, i.e., wet atmospheric deposition of acidifying industrial emissions, such as

nitrogen and sulfur oxides, is one such mechanism that reduces soil pH and can thereby

increase metal mobility and availability in soils. Jing et al. (2007) found a direct correlation

between decreasing soil pH and increasing retention of heavy metals, such as Hg. In

addition to increasing Hg and other heavy metal mobility, acid deposition can also

contribute to the methylation of mercury. Soil chemistry promotes methylation when soils

are low in oxygen (usually saturated soils), high in sulfur, and high in dissolved organic

carbon. Sulfate-reducing bacteria that convert elemental Hg to MeHg thrive in these


conditions, and thus, pollution causing acid deposition, especially of nitrogen and sulfur

oxides, enhances soil conditions for the methylation process (Scheuhammer 1987).

Methylmercury in the leaf-litter and forest floor is available to invertebrates, such as

gastropods, isopods, and insects. The incorporation of MeHg from the leaf litter by

detritivores and by predaceous invertebrate species (i.e., centipedes and spiders) that feed

on detritivores is a direct pathway to elevated Hg exposure for the next highest trophic

level, invertivores (i.e., songbirds and bats). Spiders can have a particularly influential

impact on biomagnifying MeHg in forest food webs. In Virginia, Cristol et al. (2008) found

that some terrestrial-feeding songbird species that preyed on spiders had Hg levels that

exceeded those of aquatic-feeding songbirds. Even piscivorous species, such as the Belted

Kingfisher (Megaceryle alcyon), had lower Hg body burdens than terrestrial songbird

species in that study.

Terrestrially acidified environments not only enhance methylmercury availability, they

reduce calcium availability. Correlations between increased Hg input and decreased soil

pH and calcium availability can have important ramifications on songbird breeding success,

particularly egg production and growth of hatchlings. Indeed, acid rain has been linked by

a number of studies to declines of bird species in Europe and the United States (Graveland

1990, Möckel 1992, Graveland 1998, Zang 1998, Hames et al. 2002). This phenomenon

may be linked to depletion of soil pools of extractable calcium by leaching (Likens et al.

1996, Driscoll et al. 2001), leading to decreases in the abundance of calcium-rich

invertebrate prey essential to breeding female birds as sources of calcium during egg

production and when feeding nestlings (Graveland 1996, Graveland and Drent 1997, Bures

and Weidinger 2003). Logistic regression analysis of habitat-related variables measured

by Hames et al. (2002) indicated a strong, negative relationship between acid rain and the

probability of detecting Wood Thrush (Hylocichla mustelina) breeding evidence.

Additionally, uptake and toxicity of trace metals from food have both been shown to

increase in the presence of low dietary calcium and may play an important, but as yet

undocumented, role in regional declines of terrestrial bird species (Scheuhammer 1991,

Silver and Nudds 1995, Scheuhammer 1996).

There have been very few investigations on Hg exposure in bats; however, they appear to

be capable of accumulating very high levels of Hg in their blood and fur. Miura et al. (1978)

examined various species of Chiroptera from areas in Japan sprayed with Hg fungicides and

found total fur Hg levels of approximately 33 ppm (fw). Bats may be exposed to mercury in

both industrialized and rural areas. Pipistrelle Bats (Pipistrellus pipistrellus) had elevated

levels of metals, including Hg, and pesticides in both industrial and rural areas in Sweden

(Gerell and Lundberg 1993). In Great Britain, Pipistrelle Bats showed a significant positive


trend in Hg levels over a 15-year period indicating a potential relationship with increased

atmospheric inputs and/or exposure to point sources (Walker et al. 2007).

Bats are increasingly of high conservation concern to conservation agencies and other

entities. Mercury is one anthropogenic stressor on bat populations that may be

compounded by other stressors such as wind turbines and white-nose syndrome, a disease

that has caused mass mortality among hibernating bats throughout New England and the

Mid-Atlantic States over the last four years. Therefore, high resolution investigations to

determine spatially explicit effects from Hg on reproductive success, survival, and

physiological effects are of great importance and urgency. There are several factors that

increase bats’ risk of exposure to and accumulation of mercury: (1) they are long-lived, (2)

they feed at relatively high levels in the trophic food web, and (3) they are very mobile in

comparison to other mammals of similar size.

In the interest of assessing potential impacts and injury to invertivores from atmospheric

Hg deposition, we established a network of sampling stations in New England and the Mid-

Atlantic States to assess Hg concentrations in soil, invertebrates, songbirds, and bats in

terrestrial habitats. We addressed not only the importance of spatial-scale variation of Hg

levels within ecosystems but also finer scale gradations between species, family groupings,

and foraging guilds. Our overall objective for performing this research was to identify

invertivore species prone to elevated Hg levels. Landscape characteristics shape the

ultimate fate of Hg deposited within an ecosystem and these geochemical processes have

not been well quantified. However, by determining background Hg levels in terrestrial

species across a wide geographic area in locations that are not directly affected by point

source mercury emissions, then we can begin to identify geographic areas, habitats,

taxonomic groups, and natural communities at greatest ecotoxicological risk from mercury

deposition. This information can be used to inform policy makers concerned with local,

regional, and national air quality issues.


3.0 SOILS

3.1 STUDY AREA

Soil was opportunistically collected at mistnet lanes where songbirds and invertebrates

were sampled in NY, PA, and VA (Figure 1).

Figure 1. Study area map of soil sampling locations.

3.2 METHODS

Soil samples were analyzed for total Hg at Syracuse University, Syracuse, NY using a direct

mercury analyzer. Samples collected at the Institute for Ecosystem Studies (IES) in

Millbrook, NY were analyzed for total Hg as well as exchangeable calcium (Ca), available Ca,

pH, moisture (%), potassium (K), and magnesium (Mg). Statistical analysis was performed

using Program JMP 9.0. Nonparametric Spearman’s rank correlation was used to


determine relationships between soil variables, including soil moisture, pH, Hg, Ca, K, and

Mg. Relationships were considered significant at P < 0.05.

3.3 RESULTS AND DISCUSSION

3.3.1 MERCURY LEVELS IN SOIL

Mercury levels in soil samples (N = 62) ranged from 0.06 ppm to 0.69 ppm (Figure 2). Soil

collected in the Adirondack Mts, NY, had the highest mean soil Hg concentration ( = 0.25

ppm). The highest soil Hg level detected (0.70 ppm) was collected near Arbutus Lake,

Adirondack Mts, NY. Within that region, elevated soil Hg levels were also detected in the

Tug Hill Plateau (0.39 ppm), Elk Lake (0.24 ppm), Ferd’s Bog (0.19 ppm), and Spring Pond

Bog (0.10 ppm); the lowest level was detected at Sunday Lake (0.09 ppm). Plateau Mt. in

the Catskills Mts, NY had the highest soil Hg level (0.35 ppm) collected in that region

followed by Devil’s Tombstone Campground (0.27 ppm), Lake Capra (0.22 ppm), and

Hunter Mt. (0.12); the lowest levels were collected at Emmons Bog (0.08 ppm), Neversink

Valley (0.07 ppm), and Belle Ayr Fish Hatchery (0.07 ppm). The highest level from samples

collected in the Southern NY region was from the Sam’s Point Preserve in the Shawangunk

Mts. (0.28 ppm) followed by Black Rock Forest (0.27 ppm); the lowest level observed was

at Mohonk Preserve (0.09 ppm). VA samples were collected at the Buller Fish Hatchery

(0.06 ppm) and Clinch Mt. (0.23 ppm). PA soil samples were collected at Powdermill; a

forest sample was 0.10 ppm and a sample from Spruce Bog was 0.23 ppm.

Central/Western NY soil samples were collected at Allegany State Park (0.10 ppm) and

Brookfield Railroad State Forest (0.09 ppm). The wide ranges in soil Hg at sites within the

same geographic region and/or landscape, e.g., Sam’s Point and Mohonk Preserve in the

Shawankgunk Mts., Southern NY, are likely related to landscape characteristics. Indeed,

variables such as soil moisture and chemistry play important roles regarding the ultimate

fate of Hg in soil.


Figure 2. Mean plus standard deviation and maximum level detected of Hg in soil sampled

in PA, VA, and four regions of NY. Small sample sizes precluded statistical comparisons.

3.3.2 CASE STUDY # 1 - FOREST SOILS

3.3.2.1 SOIL MOISTURE

Soil moisture plays an important role in

methylation of mercury. Increased soil moisture

creates a suitable environment for sulfate- and

iron- reducing bacteria that transform mercury to

its bioavailable form, methylmercury (MeHg)

(Wiener et al. 2003). Mercury accumulation in

soils has most often been studied in aquatic

ecosystems where production of MeHg is favored

due to the anaerobic conditions of saturated soil.

Preliminary research suggests that MeHg is not as

readily formed in terrestrial soils as compared to

wetland soils; however, as our research

illustrates, MeHg is prevalent throughout the

terrestrial food web.

Soil samples were collected at the Institute for Ecosystem Studies (IES) in Millbrook, NY

were analyzed for moisture content and Hg concentrations. Nonparametric Spearman rank

correlation analysis detected a significant positive relationship between organic soil layer

moisture and Hg concentrations; no significant trend was detected in the mineral soil layer

0.0

0.2

0.4

0.6

0.8

1.0

Soil

Hg

(pp

m)

Soil Sampling Regions

Maximum Level Detected Mean + SD


(Figure 3). Soil moisture also helps facilitate diffusion of nutrients, such as Ca, K, and Mg,

across soil gradients. Diffusion is the primary mechanism by which these vital nutrients

are delivered to root systems for uptake by plants. There was a significant and positive

relationship between calcium and soil moisture in the organic soil layer, and no significant

relationship in the mineral soil layer (organic: Spearman’s ρ = 0.45, P = 0.02; mineral:

Spearman’s ρ = 0.15, P = 0.56). We did not detect any significant relationships in our

samples between soil moisture and K (organic: Spearman’s ρ = 0.20, P = 0.34; mineral:

Spearman’s ρ = 0.21, P = 0.42) or Mg (organic: Spearman’s ρ = 0.17, P = 0.42; mineral:

Spearman’s ρ = 0.31, P = 0.23).

Figure 3. The relationship between moisture and Hg concentration in the organic and

mineral soil layers from samples (N = 31) collected at IES in Millbrook, NY (organic soil

layer: Spearman’s ρ = 0.59, P = 0.02; mineral soil layer: Spearman’s ρ = - 0.23, P = 0.38).

3.3.2.2 SOIL CHEMISTRY

Soil pH is an indication of the acidity or alkalinity of soil. It is measured in pH units ranging

from the most acidic, 0.0, to the most alkaline, 14.0, with 7.0 being neutral. Most plants

grow best in a soil pH of 6.0 to 7.0, although, some plants can tolerate levels above or below

this range. Normal soil pH ranges between 5.0 and 8.0 and levels below that range are

considered highly acidic. Acid rain causes soil to become acidic due to deposition of

hydrogen ions and by mobilization of aluminum ions, both of which displace basic cations,

such as Ca, Mg, and K, which are then leached out of the organic and mineral soil layers. Ca,

Mg, and K are mineral nutrients that are vital to plant growth and health and may be less

available in soils with low pH. Additionally, acidic soils tend to be associated with higher

retention of heavy metals, such as Hg (Jing et al. 2007). Our findings indicated that acidic

soils had higher levels of mercury and there was a significant correlation between acidity

0

50

100

150

200

250

300

0 20 40 60 80

Soil

Hg

(µg/

kg)

Soil Moisture (%)

Organic

Mineral


and mercury concentration in the organic soil layer; no significant relationship was

detected between soil pH and Hg in the mineral soil layer (Figure 4). Calcium levels in the

mineral soil layer exhibited a strong significant tendency to increase with decreasing

acidity, but there was no correlation between pH and calcium in the organic soil layer

(Figure 5).

Figure 4. Relationship between pH and Hg concentrations in organic and mineral soil layers

in samples (N = 31) collected at IES in Millbrook, NY (organic soil layer: Spearman’s ρ = -

0.81, P = 0.0002; mineral soil layer: Spearman’s ρ = - 0.15, P = 0.57).

Figure 5. Relationship between pH and exchangeable calcium (Ca) concentrations in

organic and mineral soil layers in samples (N = 42) collected at IES in Millbrook, NY

(organic soil layer: Spearman’s ρ = 0.27, P = 0.18; mineral soil layer: Spearman’s ρ = 0.80, P

= 0.0001).

0

50

100

150

200

250

300

0 1 2 3 4 5 6 7

Soil

Hg

(µg/

kg)

Soil pH

Organic

Mineral

0

2

4

6

8

10

12

0 1 2 3 4 5 6 7

Soil

Exch

ange

able

Ca

(cm

olc

/kg)

Soil pH

Organic Mineral


Our results also indicated an inverse relationship between available K and Mg and acidity

in the mineral soil layer; no significant relationships were detected in organic soil layer

samples (Figures 6 & 7). Potassium is a primary macronutrient and is consumed in large

quantities by plants to help in protein building, photosynthesis, fruit production, and

disease prevention. Magnesium is a micronutrient and is consumed in smaller quantities

but it is part of the chlorophyll necessary for photosysnthesis and also plays a role in

activating enzymes necessary for plant growth. These elements were strongly correlated

with one another in our soil samples (Spearman’s ρ = 0.75, P < 0.0001). They were also

each strongly correlated with the amount of available Ca (Mg to Ca: Spearman’s ρ = 0.84, P

< 0.0001; K to Ca: 0.54, P = 0.0002). In addition to calcium’s role in uptake by invertebrates

that provide calcium needs required by breeding birds, it is a vital nutrient for plant health.

Calcium is a critical component of plant cell wall structure, which faciliates transport and

retention of other elements, and provides strength in the plant. However, these valuable

nutrients are less available in acidic soils due to leaching out (Nihlgard 1985). Therefore,

to uncover mercury’s effect on ecosystem structure and function, it is important to consider

other interacting ecological stressors which may be at play. Such is the case where

acidifying emissions have the ability to drastically alter the chemical structure of soils and

plants, and thereby affect Hg mobility and availability in soil.

Figure 6. Relationship between pH and exchangeable potassium (K) in the organic and

mineral soil layers in samples (N = 42) collected at IES in Millbrook, NY (organic soil layer:

Spearman’s ρ = -0.31, P = 0.13; mineral soil layer: Spearman’s ρ = 0.47, P = 0.05).

0.0

0.5

1.0

1.5

2.0

2.5

0 1 2 3 4 5 6 7

Soil

Exch

ange

able

K (

cmo

lc/k

g)

Soil pH

Organic

Mineral


Figure 7. Relationship between pH and exchangeable magnesium (Mg) in the organic and

mineral soil layers in samples (N = 42) collected at IES in Millbrook, NY (organic soil layer:

Spearman’s ρ = -0.33, P = 0.10; mineral soil layer: Spearman’s ρ = 0.61, P = 0.009).

3.4 CONCLUSION

Deposition of acidifying emissions and heavy metals has a profound effect on forest

ecosystems. Acid rain is a complex solution of primarily H+, SO42- , NH4+, and NO3- pollutant

ions. Vegetation damage may occur through direct exposure to air pollutants or

acidification of soil. Acid-induced leaching of plant nutrients, primarily magnesium and

potassium, may result in reduced forest health. Additionally, leaching may be responsible

for a 50% loss of calcium pools in soils over the last 50 years (Likens et al. 1996). Once the

soil is acidified, it is prone to acidifying nearby surface waters and retaining elevated levels

of toxic heavy metals, such as aluminum and mercury. The pathways for accumulation of

mercury in terrestrial ecosystems are not fully understood, but recent work suggests that

accumulation involves absorption of gaseous mercury (Hgº) by foliar tissue of deciduous

trees (Ericksen et al. 2003, Frescholtz et al. 2003) and needles in coniferous trees, with

subsequent release of mercury in litterfall (Rea et al. 2002, Ericksen et al. 2003, Frescholtz

et al. 2003). While litterfall may represent the bulk of mercury input to forested

ecosystems, the wash-off of dry-deposited Hg species in throughfall, direct deposition in

precipitation, and uptake of dissolved mercury by roots and translocation to foliar tissue

may also play roles (Rea et al. 2002). Litterfall and throughfall deliver different forms of

mercury to the forest floor and this may strongly influence the retention of mercury and its

ultimate fate in terrestrial ecosystems. In any case, total mercury (THg) inputs to eastern

forests are largely incorporated in the leaf-litter and topmost layers of soils, where it is

available to invertebrate detritivores, such as gastropods (snails and slugs), isopods

(woodlice), myriapods (millipedes), and to soil-dwelling annelids (earthworms).

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0 1 2 3 4 5 6 7

Soil

Exch

ange

able

Mg

(cm

olc

/kg)

Soil pH

Organic

Mineral


Therefore, we must also monitor Hg concentrations in invertebrate species to positively

identify the soil and leaf litter layers as significant pathways for Hg to enter the food web.

4.0 INVERTEBRATES

4.1 STUDY AREA

Invertebrates were opportunistically collected along mist net lanes at songbird sampling

stations in ME, NH, NY, PA and WV (Figure 8).

Figure 8. Invertebrate sampling locations in New England and the Mid-Atlantic States,

2005 to 2008, and 2010.

4.2 METHODS

Four wet cardboard traps, each placed 20 m from the center point of the site in the four

cardinal directions were used to sample invertebrates in the leaf litter. Each trap was a 1 ft.

x 1 ft. (30.5 cm x 30.5 cm) square of plain (uncoated) corrugated cardboard. At least one

side, which was placed downward, was free of printing or glue. The traps were placed in

the afternoon or evening and checked the following morning. Each trap was set by holding

the cardboard at an angle of about 45° with one side touching the ground and then slowly


pouring approximately 1 liter of non-chlorinated water across the top surface of the

cardboard. The cardboard was then placed (wet side down) in the wet area in the leaf litter

where the excess water ran off. A few sticks or stones were placed on top of each trap to

hold it in place. Additional invertebrates were collected by using pitfall traps that were left

out for varying lengths of time. Specimens were collected and stored in 95% ethyl alcohol

until they were analyzed for MeHg content, which was reported as parts per million dry

weight (ppm, dw) content.

4.2.1 STATISTICAL ANALYSIS

Statistical analysis was conducted in JMP 9.0. Arithmetic means are presented in graphs;

however, invertebrate Hg concentrations were log-transformed prior to statistical analysis

and checked for normality with the Shapiro-Wilk test. Homogeneity of variance was

examined in normal data sets with the Bartlett’s test and in non-normal data sets with the

Fligner-Killeen test, which is less sensitive to outliers. If normality and equal variance

assumptions were met, differences between groups (e.g., sampling regions) were checked

with t-tests or ANOVA and Tukey’s honestly significant difference test. Non-normal

datasets with equal variance among groups were examined with the nonparametric

Kruskal-Wallis and Wilcoxon rank sum tests. Tests were considered significant at P < 0.05.


4.3.1 SAMPLING EFFORT

During 2005 to 2010, we sampled 371 invertebrates from 13 orders in 9 regions of New

England and the Mid-Atlantic States. Diptera, Amphipoda, and Araneae species had the

highest mean MeHg concentrations (Figure 9).

4.3.2. REGIONAL AND SPECIES MERCURY EXPOSURE

All Dipteran and Amphipoda samples were collected in salt marsh habitat in coastal MA

(Parker River NWR) and coastal ME (Rachel Carson NWR). Those collected in coastal MA

had significantly higher MeHg concentrations compared to those collected in coastal ME

[Diptera: MA ( = 0.39 ± 0.22 ppm, N = 29) vs. ME ( = 0.17 ± 0.08 ppm, N = 25), (P <

0.0001); Amphipoda: MA ( = 0.29 ± 0.11 ppm, N = 15) vs. ME ( = 0.26 ± 0.49, N = 15), (P <

0.0001)]. Additionally, Araneae spiders species collected in coastal MA had significantly

higher MeHg levels than all other regions where they were sampled (P < 0.0001) (Figure

10).


Figure 9. Mean plus standard deviation and maximum levels detected of MeHg

concentrations in invertebrate orders sampled in New England and Mid-Atlantic States,

2005 to 2010.

Figure 10. Regional means plus standard deviation and maximum levels detected of MeHg

concentrations in Araneae species sampled in New England and Mid-Atlantic States, 2005

to 2010. Coastal MA Araneae species had significantly higher MeHg concentrations

compared to other sampling locations (P < 0.0001).

0.0

0.5

1.0

1.5

2.0

2.5

Me

Hg

(pp

m),

dw

Maximum Level Detected

Mean + SD

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Catskill Mts, NY (N = 15)

PA (N = 10)

Coastal ME (N = 13)

Southern NY (N = 18)

Coastal MA (N = 14)

Adirondack Mts, NY

(N = 115)

Me

Hg

(pp

m),

dw

Araneae Sampling Regions


Mean + SD


Invertebrates sampled from Parker River NWR likely exhibited such high Hg levels because

sampling efforts were concentrated in the salt marsh situated between the Merrimack and

Parker Rivers. Both rivers carry waters from interior watersheds to the coast. The middle

and lower Merrimack River is a well known Hg hotspot due to high atmospheric deposition

rates and historic point source pollution (Evers et al. 2007). Benthic fauna, such as

amphipods, are good indicators of soil contamination. Amphipods are bottom-dwellers

that filter-feed on suspended particulate matter and deposit feed on detritus and sediment.

Therefore, they are at high risk to toxin accumulation due to their proximity and long-term

exposure to soil pollution (DeWitt et al. 1992). George et al. (2001) found that amphipods

contained higher concentrations of Hg than other higher trophic level organisms, such as

odonates and crayfish. The bioavailability of MeHg in benthic organisms at contaminated

sites appears to reach a seasonal high during summer and autumn months (Zizek et al.

2007). This seasonal variability increases the potential for magnification of mercury in

higher trophic levels, particularly in songbirds, many of which have breeding season diets

reliant on invertebrate prey.

The proportion of bioavailable MeHg to THg in predatory invertebrates that prey upon

other predatory invertebrates, e.g., heteropterans, coleopterans, odonates, is 70% to 95%,

compared to 35% to 50% in detritivores-grazers (dipterans, ephemeropteran,

trichopterans) (Tremblay et al. 1996). Therefore, predatory invertebrates are at great risk

of Hg accumulation. Indeed, Tremblay et al. (1996) found that MeHg concentrations in

predatory invertebrates were 3 times greater than levels found in detritivores. They

attributed several abiotic factors, including temperature, oxygen concentration,

atmospheric deposition and the organic content of the sediment, as determining factors of

the availability of MeHg to low trophic level organisms. Dipteran samples in this study

were primarily from the Tabanus genus, which are blood-sucking horse flies that fall into

the predatory invertebrate category. Rimmer et al. (2010) studied Hg levels of

invertebrates in a montane forest habitat and found a mean THg level in Dipterans of 0.11 ±

0.17 ppm and range of 0.002 to 0.982 ppm. Spiders are also predatory invertebrates and

those sampled at coastal sites and in the Adirondack Mts, NY, had the highest mean MeHg

concentrations among sampling regions. MeHg concentrations in spiders ranged from

0.006 ppm, dw (Dome Island, NY) to 2.02 ppm (Rachel Carson NWR, ME). The highest

MeHg levels in spiders in the Adirondack Mts were primarily from species collected on

Dome Island in Lake George, which is discussed in greater detail below in Case Study # 2.


4.3.3 CASE STUDY # 2 -DOME ISLAND SPIDERS

(BUCK ET AL. 2011)

Lake George is a large (114 km2) meso-

oligotrophic lake in northeastern New York

and is in the southeastern most portion of

Adirondack Park. Dome Island, located within

the southern basin, is a small island (~6.1

hectares) with approximately 1100 m of

shoreline. It is the highest elevated island on

Lake George and nearly one mile from the

nearest mainland (Figure 11). The island is a

mix of deciduous and coniferous forest, such as

red maple (Acer rubrum), paper birch (Betula

papyrifera), white pine (Pinus strobus) and eastern hemlock (Tsuga canadensis).

Figure 11. Map of Lake George, NY

showing the location of Dome Island

in the southern basin (inset map

shows the location of Lake George in

northwest NY state).

All observed spiders along transect

lines were collected yielding a

sample size of 309 spiders,

representing 8 different families and

4 different foraging guilds.

Individual spiders from the same

transect and taxonomic families

were composited to provide

sufficient mass for a combined

analysis of total mercury,

methylmercury, and stable carbon

and nitrogen isotopes. This resulted in a total of 81 spider samples. Total and

methylmercury were analyzed to provide information about differences in Hg exposure

across sites and across foraging guilds. Stable isotopes were analyzed to provide

information about food web structure and the transfer of contaminants between trophic

levels.


Total mercury (THg) concentrations measured in spiders ranged from 0.040 ppm, dry

weight (dw), to 1.63 ppm, dw, with an overall mean concentration of 0.254 ppm, dw. The

amount of highly bioavailable methylmercury (MeHg) in spiders ranged from 33.5 ± 8.1%

to 52.7 ± 6.4% of THg. These values are higher than reported THg concentrations for

spiders from forested areas in southern Vermont not affected by point source pollution

(Rimmer et al. 2010; mean THg = 0.173 ppm, dw), but are lower that mean THg

concentrations in spiders from the South River, Virginia, a river impacted by point source

mercury pollution for many decades (Cristol et al. 2008; mean THg = 1.24 ppm, dw).

The most abundant foraging guild of spider collected from Lake George sites were Orb-

weaving spiders (Families Tetragnathidae and Araeidae). These spiders are abundant in

riparian and littoral zone habitats and, along with Cursorial predatory spiders (e.g., Family

Lycosidae), have been the focus of other contaminant studies linking terrestrial and aquatic

ecosystems (Cristol et al. 2008; Walters et al. 2010). Orb-weaving spiders collected at

water’s edge sites on islands (combined data from Crown and Dome Islands) had

significantly higher THg concentrations than the Mainland water’s edge site.

Changes in the nitrogen isotopic concentration (δ15N) of spiders reflect changes in food

web complexity and trophic level interactions and when examined in concert with

mercury, provide an integrated assessment of contaminant transfer and biomagnification

up through a food web. There is a strong correlation (r = 0.565) between the %MeHg and

δ15N of Orb-weaving spiders collected from the water’s edge transects. Orb-weaving

spiders from the water’s edge are the only sub-group of spiders where this relationship had

a strong correlation. Overall these results suggest that bioaccumulation of Hg in Orb-

weaving spiders along the water’s edge is related to increasing food web complexity and

suggests there may be a Hg pathway linking the adjacent aquatic environment to terrestrial

food webs.

High levels of mercury in the songbirds and spiders from BRI’s previous work at Dome

Island raised concerns that high levels of mercury deposition were occurring at the site. To

address this question, we acquired one of the few portable wet Hg deposition collectors in

the country, and stationed it at Lake George during September-October 2009. Weekly wet

Hg deposition data for Lake George ranged between 7.5 and 205.6 ng/m2. These data

exhibit similar weekly trends as data from other long-term Hg deposition monitoring sites

in NY State, suggesting that Hg deposition is not a primary driver for the high Hg

concentrations observed in biota of Dome Island.

A consistent challenge with Hg exposure studies is not only quantifying how much Hg is

being deposited, but identifying potential sources of the Hg that is entering the ecosystem.


While advances are being made to differentiate Hg sources using stable Hg isotopes within

food webs that have only two end members (e.g., Senn et al. 2010), to date, this has not

been done successfully with atmospheric sources, largely due to the multiple sources of Hg

that contribute to the atmospheric Hg pool and the difficulty with separating out sources

within a multi-end member model. However, an exhaustive literature review of potential

Hg sources within the Adirondacks region suggests that Hg sources can be divided into four

primary contributors including: (1) natural emissions, (2) New York-based industrial

sources, (3) U.S.-based sources; and (4) Hg emitted from sources within the Asian

continent (Seigneur et al. 2003). The timing and associated weather pattern of

precipitation events can also influence the degree to which local versus regional/global

sources influence Hg deposition in the Adirondacks region (Choi et al. 2008). For some

lakes in the Adirondacks region, local and regional emissions sources can account for as

much as 80% of the total Hg flux (Bookman et al. 2008). We present a summary of

potential local emissions sources proximate to Lake George including local aggregate and

cement producing plants. Reductions of Hg emissions from local sources can result in

significant reductions of Hg in biota (Evers et al. 2007; Hutcheson et al. 2008) and a

continued effort that combines a science-based program with local community engagement

and clear communication with local- and national-level policy makers can result in greater

reductions in Hg emissions and the reduction of human and ecological health risks

associated with Hg pollution.

4.4 CONCLUSION

The detritus food web is the likely source of elevated Hg levels in soil-dwelling

invertebrates. In the case of the salt marsh ecosystem, we saw that soil-dwelling isopods

were capable of accumulating exceptionally high Meg levels from the detritus food web.

Higher Hg concentrations detected in predatory invertebrates, such as spiders and blood-

sucking flies, represent possible mechanisms of bioaccumulation within lower trophic

levels of the food web. The biological significance of these findings are the implications

these elevated MeHg levels have on higher trophic levels that feed on invertebrates,

including fish, bats, and songbirds. While the role of elevated Hg in fish and the negative

effects it has on both human and wildlife health have been and continue to be well-studied

and documented, the repercussions of elevated Hg in bats and songbirds, particularly those

in terrestrial habitats, are less recognized and poorly understood.

Soil- and litter-dwelling invertebrates may comprise a significant portion of the diet of

litter-feeding birds, with snails and slugs estimated to comprise 2.5% of the animal

biomass and 6% of the available energy (Hawkins et al. 1997) in boreal forest ecosystems.

Some of these invertebrates (snails, woodlice, millipedes and centipedes) may also

represent crucial sources of calcium to many breeding birds (Graveland and van der Wal

1996, Bures and Weidinger 2003) and the abundance of all of these potential prey species


decline with declines in soil pH (Graveland 1996, Graveland and van der Wal 1996, Bures

and Weidinger 2003). Indeed, healthy soil and invertebrates are critical building blocks

necessary for survival of all vertebrate animals. In the next section, we will expand our

sampling locations and explore Hg pathways in songbird species, habitats, and foraging

guilds.

5.0 SONGBIRDS

5.1 STUDY AREA

Songbirds were sampled at 165 locations in 11 New England and Mid-Atlantic States:

Connecticut, Delaware, Maine, Massachusetts, New Hampshire, New York, Pennsylvania,

Rhode Island, Vermont, Virginia, and West Virginia (Figure 12).

5.2 METHODS

Sampling efforts were timed for June and July to allow time for depuration of Hg body

burdens that could reflect winter and/or migratory MeHg uptake. It is well established that

blood reflects recent dietary uptake of MeHg (Evers et al. 2005). Typically, 8 to 10, 12 m

mist nets with a 36 mm mesh size were used to catch songbirds. Nets were placed on

bamboo and/or metal poles. The nets were checked every 20 to 40 minutes. Captured birds

were removed and placed in cotton holding bags until processed. All birds were released

unharmed 15 to 45 minutes after capture. Birds were captured during both dawn and dusk

periods. All birds were measured using standard wing, tail, tarsi, bill, and mass

measurements, and banded with USGS bands. For all birds, 28-gauge disposable needles

were used to puncture a cutaneous ulnar vein in the wing to collect a small blood sample.

Each blood sample was collected in a 75 uL capillary tube, which was then sealed on both

ends with Crito-seal or Critocaps ® and placed in a labeled plastic 7 cc vacutainer.

Generally, 2 to 4 capillary tubes half-filled with blood were taken from each bird. The

feathers were placed in a labeled plastic bag. All samples were stored in a field cooler with

ice, and samples were later transferred for temporary storage (blood in the freezer,

feathers in the refrigerator). Samples were analyzed for total mercury (THg) and reported

as parts per million wet weight (ppm, ww). THg approximates MeHg, which is 90 to 100%

of THg in avian blood (Rimmer et al. 2005).

5.2.1 STATISTICAL ANALYSIS

Statistical analysis was conducted in JMP 9.0. Arithmetic means are presented in graphs;

however, blood Hg concentrations were log-transformed prior to statistical analysis and

checked for normality with the Shapiro-Wilk test. Homogeneity of variance was checked

with Bartlett’s test. If normality and equal variance assumptions were met, differences

between groups were checked with t-tests or ANOVA and Tukey’s honestly significant

difference test. Non-normal datasets with equal variance among groups were examined

with the nonparametric Kruskal-Wallis and Wilcoxon rank sum tests (p < 0.05).


Figure 12. Study area map of songbird sampling locations.



5.3.1 SAMPLING EFFORT

A total of 1,878 songbirds representing 78 species were sampled at 165 locations within 20

geographic regions of New England and Mid-Atlantic States (Figure 13). Sample sizes of

each species ranged from 1 to 494 and blood Hg levels ranged from 0.0005 ppm (American

Goldfinch, Spinus tristis) to 3.73 ppm (Saltmarsh Sparrow, Ammodramus caudacutus).

Figure 13. Regional means plus standard deviations and maximum levels detected of blood

Hg levels (ppm) in songbirds sampled in New England and Mid-Atlantic States, 1999 to

2007.

5.3.2 REGIONAL AND SPECIES MERCURY EXPOSURE

Mercury hotspots are geographic locations with disproportionately elevated Hg levels

(Evers et al. 2007). The mechanisms that drive these trends include elevated atmospheric

Hg deposition, high landscape sensitivity, large water-level manipulations, and direct Hg

input from water discharges and contaminated soils. Abiotic and biotic features of sites

with these characteristics are predicted to have elevated Hg levels corresponding with the

rate of deposition and degree of landscape sensitivity and disturbance. We focused our

sampling at sites not associated with direct point source Hg pollution in order to determine

background Hg levels in songbirds that could be primarily attributed to atmospheric

deposition. Our results indicated that songbirds at coastal sites averaged the highest mean

blood Hg levels. Specifically, high Hg levels at coastal sites were found primarily in

Saltmarsh Sparrow, Nelson’s Sparrow (Ammodramus nelsoni), and Seaside Sparrow

(Ammodramus maritimus). Pairwise comparisons among coastal sparrow species indicated

that Saltmarsh Sparrow mean blood Hg levels were significantly higher than Nelson’s

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Me

an B

loo

d H

g (p

pm

), w

w

Songbirds Sampling Areas


Mean + SD


Sparrow (p < 0.0001), but no other significant differences existed among that group.

Elevated blood Hg levels in coastal sparrows are discussed in greater detail below in Case

Study #3.

High mean blood Hg levels detected in songbirds in NH, VT, Western and Northern ME are

primarily due to extremely high levels found in Rusty Blackbirds (Euphagus carolinus) and

this research is highlighted below in Case Study #4. The overall mean blood Hg of

songbirds sampled in Southwest VA along the Holston River is relatively low; however,

maximum levels detected for certain species were very high (Figure 14). In particular,

Indigo Buntings (Passerina cyanea) in this region had the highest mean blood Hg

concentration of 0.28 ± 0.50 ppm (N = 10) and a maximum level of 1.67 ppm. During the

breeding season, Indigo Buntings feed on small spiders and insects, such as caterpillars,

beetles, and grasshoppers (Payne 2006). Songbirds that prey on higher trophic level

invertebrates, such as spiders, increase their risk of Hg exposure and biomagnification.

Cristol et al. (2008) analyzed spiders from this region and found that 49 ± 21% of their

total Hg body burden was in the highly available form, MeHg, which is readily absorbed

into the blood. Spiders in the riparian zone are potentially exposed to MeHg in the aquatic

system if they feed on emergent aquatic insects. However, more research is necessary to

determine whether predatory invertebrates represent a direct pathway for Hg to move

from the aquatic food web into the terrestrial food web.

Songbirds sampled within the Adirondack Park, NY region with the highest mean and

maximum blood Hg levels, including Yellow Palm Warbler (Dendroica palmarum) ( = 0.57

± 0.41 ppm, max = 1.49 ppm), Traill’s Flycatcher (Empidonax traillii) ( = 0.36 ± 0.26 ppm,

max = 0.71 ppm), and Lincoln’s Sparrow (Melospiza lincolnii) ( = 0.19 ± 0.19 ppm, max =

0.66 ppm), were sampled in bog wetlands (Spring Pond Bog and Massawepie Mire) (Figure

15). Bog soils are low in dissolved oxygen and nutrients and are highly acidic; therefore,

Hg is easily converted to MeHg in bog habitat. Yu et al. (2010) found that Sphagnum moss

mats were prime locations for MeHg production and accumulation in bog wetlands in the

Adirondack region. They proposed that submerged sponge-like structures of the plant are

colonized by microorganisms capable of methylating Hg, such as sulfate-reducing bacteria.

Furthermore, Hg is readily sorbed by moss tissues and methylation is facilitated by the

anaerobic conditions around underwater plant parts. Spiders collected at Spring Pond Bog

and Massawepie Mire had elevated MeHg levels; 0.34 ± 0.11 ppm and 0.15 ± 0.09 ppm,

respectively. Spiders make up only a small portion of the primarily insectivorous breeding

season diet of Yellow Palm Warbler, Traill’s Flycatcher, and Lincoln’s Sparrow; however, it

is likely that their primary prey, e.g., beetles, flies, moths, within the same area would also

be prone to elevated MeHg levels. Yellow Palm Warblers and Lincoln’s Sparrows feed

primarily on the ground on their breeding habitat and are therefore excellent bioindicators

of Hg levels within the bog wetland food web.


Figure 14. Mean plus standard deviation and maximum level detected of blood Hg

concentrations in songbirds sampled in Southwest VA, 2005 to 2007.


concentrations in songbirds sampled in Adirondack Mts, NY region, 2006 and 2007.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Am

eric

an G

old

fin

ch (

N =

2)

Slat

e-co

lore

d J

un

co (

N =

1)

Bla

ck-t

hro

ated

Gre

en W

arb

ler

(N =

1)

Car

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a C

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ee (

N =

1)

No

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(N

= 1

)

No

. Ro

ugh

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ged

Sw

allo

w (

N =

2)

Gra

ssh

op

per

Sp

arro

w (

N =

1)

Bla

ck-t

hro

ated

Blu

e W

arb

ler

(N =

1)

Ho

od

ed W

arb

ler

(N =

1)

Ced

ar W

axw

ing

(N =

5)

Bla

ck-a

nd

-Wh

ite

War

ble

r (N

= 1

)

Blu

e-w

inge

d W

arb

ler

(N =

1)

Yello

w-t

hro

ated

Vir

eo (

N =

1)

Ove

nb

ird

(N

= 2

)

Scar

let

Tan

ager

(N

= 1

)

Vee

ry (

N =

11

)

Wo

rm-e

atin

g W

arb

ler

(N =

2)

Co

mm

on

Gra

ckle

(N

= 3

)

East

ern

Tu

fted

Tit

mo

use

(N

= 1

)

Am

eric

an R

ob

in (

N =

5)

Gre

at C

rest

ed F

lyca

tch

er (

N =

1)

East

ern

Ph

oeb

e (N

= 2

)

Wh

ite-

bre

aste

d N

uth

atch

(N

= 1

)

No

rth

ern

Car

din

al (

N =

2)

Son

g Sp

arro

w (

N =

75

)

Wo

od

Th

rush

(N

= 1

2)

Yello

w-t

hro

ated

War

ble

r (N

= 2

)

Red

-eye

d V

ireo

(N

= 6

)

Car

olin

a W

ren

(N

= 2

8)

Aca

dia

n F

lyca

tch

er (

N =

12

)

Lou

isia

na

Wat

erth

rush

(N

= 7

)

Red

-win

ged

Bla

ckb

ird

(N

= 1

6)

Ind

igo

Bu

nti

ng

(N =

10

)

Blo

od

Hg

Leve

l (p

pm

, ww

)

Songbird Species Sampled in Southwest VA


Mean + SD

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Blo

od

Hg

Leve

l (p

pm

, ww

)

Songbird Species Sampled in Adirondack Mts, NY


Mean + SD


5.3.2.1 CASE STUDY #3 - SALTMARSH SPARROW

(LANE ET AL. 2011)

The Saltmarsh Sparrow has a limited range,

occupying estuaries along the Atlantic Coast

from Florida up to the southern coast of Maine

where it overlaps with the Nelson’s Sparrow

(Hodgman et al. 2002). They are obligate salt

marsh passerines with more than 95% of their

global population breeding in the northeastern

United States. The US Fish and Wildlife Service

(USFWS) consider them one of the highest

priority species in the northeast region and

classified them as a “bird of conservation concern”.

This designation results from the near endemic status of this species in the region, a lack of

population trend data, and threats on their breeding and wintering grounds.

Saltmarsh Sparrows spend their entire annual cycle in salt marsh habitats, thus, they are

excellent indicators of Hg contamination for this habitat type. Lane et al. (2011) sampled

Saltmarsh Sparrow blood from estuaries from Maine to New York. Results revealed that

blood Hg levels were highest at Parker River NWR in coastal MA ( = 1.80 ± 0.14 ppm).

Nonparametric pairwise comparisons indicated that coastal MA blood levels were

significantly higher than all other sampling locations (Figure 16, P < 0.01). Blood Hg levels

were lowest at coastal CT and ME sites and they were significantly lower than MA, NY, and

RI blood levels (P < 0.0001). Research conducted by Lane and Evers (2007) suggested that

Saltmarsh Sparrow reproduction may be impaired by higher blood Hg concentrations.

Based on one year of limited nest monitoring, productivity parameters such as number of

eggs hatching and fledging appeared to be significantly lower at Parker River NWR, MA

compared to Rachel Carson NWR, ME. Adult female Saltmarsh Sparrow blood Hg

concentration were positively correlated with their nestling’s blood Hg levels, indicating

that health of their young are compromised at hatching due to the deleterious effects of

mercury.

The ground-foraging habits of Saltmarsh Sparrows put them at high risk to mercury

exposure in contaminated environments. On Long Island, New York, Merriam (1979)

found that the two most common insect orders in their diet were Diptera, ranging between

13% in June to 47% of all items in July (predominantly adults and larvae of Stratiomyidae)

and Hemiptera, ranging between 4% in June to 37% in July (nymphs and adults of Miridae).

Additionally, their breeding-season diet may be comprised of up to 15% amphipod matter

(Merriam 1979). Our study found that Dipterans and Amphipods have elevated Hg levels

at coastal ME and MA sites. This example highlights a direct Hg pathway through several

Photo provided by BRI staff


orders of the food web. Mud-dwelling amphipods accumulate Hg while feeding on

contaminated detritus in the soil and pass it to Saltmarsh Sparrows. Furthermore, it is

passed to their nestlings thereby potentially reducing fledging success.

Figure 16. Mean plus standard deviation and maximum level detected of blood Hg in

Saltmarsh Sparrows sampled in coastal New England and Long Island, NY, 2000 to 2007.

5.3.2.2 CASE STUDY #4 - RUSTY BLACKBIRD

(EDMONDS ET AL. 2010)

Rusty Blackbirds breed in boreal bogs, marshes,

ponds, and swamps of Alaska, Canada and

northeastern US and winters in the wooded

wetlands of the southeast-central US. Their

populations have declined by an estimated 90%

over the last 100 years and continue to decline at

a significant rate of 13% per year (Sauer et al.

2008, Greenberg and Droege 1999). These losses

are likely attributable to factors resulting in

habitat loss and degradation, such as logging,

development, drying of wetlands due to climate change, and increases in environmental

contaminants. One such contaminant is mercury; the accumulation of which has been

shown to have negative effects on the reproductive success of a closely related blackbird,

Common Grackle (Quiscalus quiscula) (Finley et al. 1979, Heinz et al. 2009). Rusty

Blackbirds may be at even greater risk to Hg exposure than other blackbird species because

of their dietary preference for higher level trophic items, such as small fish and aquatic

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Coastal CT (N = 32)

Coastal NY (N = 27)

Coastal RI (N = 55)

Coastal ME (N = 220)

Coastal MA (N = 145)

Blo

od

Hg

(pp

m),

ww

Saltmarsh Sparrow Sampling Regions


Mean + SD


invertebrates (Avery 1995). Additionally, habitat type plays a critical role in Hg exposure

and recent research suggests that Rusty Blackbird breeding habitat is characterized by high

levels of dissolved organic carbon and low pH, which have both been correlated with

increased methylation, bioavailability, and retention of Hg (Scheuhammer 1991, O’Driscoll

et al. 2005, 2006, Harding et al. 2006).

In order to assess whether these factors resulted in high uptake of Hg by these declining

populations, Edmonds et al. (2010) sampled Rusty Blackbirds in five regions across their

range. Results indicated that geographic and seasonal differences in Hg concentrations

existed among these regions. The blood Hg levels in birds sampled on the breeding range

were significantly higher than those sampled on the wintering range. Of all the regions, the

Northeast (Acadian Forests region) breeding region samples exhibited the highest Hg

concentrations with levels 3× to 7× greater than any other region. Overall mean percent

MeHg of THg was 98 ± 2% (N = 5) in blood and 97 ± 0.3% (N = 5) in feathers. Within New

England, BRI sampled 93 Rusty Blackbirds between 2004 and 2010. Overall mean blood

Hg concentration was 0.66 ± 0.41 ppm. The highest blood Hg level (2.05 ppm) was

sampled in NH (Figure 17).

The direct effects of elevated Hg concentrations on Rusty Blackbird populations are

unclear. Reduced hatching success has been observed when THg levels in feathers were

between 5 and 40 ppm, ww (Burger and Gochfeld 1997). Over 95% of the Acadian forest

feather samples in Edmond et al.’s (2010) study exceeded this upper limit; however, Powell

(2008) reported high nesting success of Rusty Blackbirds within this range. Feather

sample results suggested that Rusty Blackbirds accrued much of their Hg burden on the

breeding grounds. Blood level results, which indicate exposure from food consumed

during the previous few days or weeks, also indicated that birds were exposed to the

highest amounts of Hg while on the breeding grounds, particularly in the Northeast (Evers

et al. 2005). Further research will be necessary to uncover potential links between

elevated blood Hg concentrations and hatching success and survival rates of this species.

Rusty Blackbird populations have suffered long-term declines over the last 100 years with

an alarming acceleration in recent decades and these trends warrant immediate attention

from conservation biologists and policy makers.


Figure 17. Regional mean plus standard deviation and maximum level detected of blood Hg

concentrations detected in Rusty Blackbirds in New England, 2007 to 2010.

5.3.3 MERCURY EXPOSURE BY FORAGING GUILD

Foraging guild is an important factor when assessing risk of Hg exposure in songbirds.

Evers et al. (2005) ranked Hg exposure risk in avian foraging guilds from lowest to greatest

as terrestrial herbivores, aquatic herbivores, terrestrial insectivores, benthivore-bivalves,

benthivore-macroinvertebrates, small piscivores, and large piscivores. Piscivorous birds

have long been used as indicators of MeHg availability (e.g., Fimreite et al. 1974; Barr 1986;

Scheuhammer 1987; Wolfe et al. 1998; Rumbold et al. 2001; Henny et al. 2002; Evers et al.

2003); however, our findings and other research (Wolfe and Norman 1998; Gerrard and St.

Louis 2001; Adair et al. 2003) reveal that insectivorous birds are also useful gauges of Hg

exposure within terrestrial habitats.

In order to determine which feeding habits increased risk of Hg exposure, we compared

mean blood Hg levels of sampled birds among the following foraging guilds (De Graaf et al.

1985):

*Note: See Appendix A for latin names of songbirds in the following list.

Frugivore Air/Upper-Canopy

Cedar Waxwing

Omnivore Upper-Canopy

Rose-breasted Grosbeak

Insectivore Air/Lower-Canopy

American Redstart

Hooded Warbler

Omnivore/Vermivore Ground/Lower-

Canopy

American Robin

0.0

0.5

1.0

1.5

2.0

2.5

Blo

od

Hg

Leve

l (p

pm

, ww

)

Rusty Blackbird Sampling Areas


Mean + SD


Insectivore Upper-Canopy

Cerulean Warbler

Northern Parula

Black-throated Green Warbler

Blackpoll Warbler

Scarlet Tanager

Red-eyed Vireo

Yellow-throated Vireo

Insectivore Bark

Black-and-White Warbler

Brown Creeper

White-breasted Nuthatch

Red-breasted Nuthatch

Insectivore Lower-Canopy

White-eyed Vireo

Prairie Warbler

Black-throated Blue Warbler

Boreal Chickadee

Blue-winged Warbler

Blue-headed Vireo

Tufted Titmouse

Black-capped Chickadee

Magnolia Warbler

Myrtle Warbler

House Wren

Common Yellowthroat

Carolina Wren

Omnivore Lower-Canopy

Carolina Chickadee

Indigo Bunting

Omnivore Ground/Lower-Canopy

American Goldfinch

Veery

Brown Thrasher

Gray Catbird

Swainson's Thrush

Bicknell's Thrush

Song Sparrow

Insectivore Air

Northern Rough-winged Swallow

Eastern Kingbird

Yellow-bellied Flycatcher

Barn Swallow

Least Flycatcher

Great Crested Flycatcher

Eastern Phoebe

Cliff Swallow

Tree Swallow

Acadian Flycatcher

Traill's Flycatcher

Eastern Wood-Pewee

Insectivore Bark/Upper-Canopy

Yellow-throated Warbler

Insectivore Freshwater Shoreline

Louisiana Waterthrush

Northern Waterthrush

Insectivore Ground

Mourning Warbler

Ovenbird

Winter Wren

Worm-eating Warbler

Yellow Palm Warbler

Rusty Blackbird


Insectivore Marsh

Marsh Wren

Omnivore Ground

White-throated Sparrow

Savannah Sparrow

Bobolink

Slate-colored Junco

Grasshopper Sparrow

Hermit Thrush

Eastern Towhee

Wood Thrush

Chipping Sparrow

Common Grackle

Lincoln's Sparrow

Northern Cardinal

Swamp Sparrow

Red-winged Blackbird

Seaside Sparrow

Nelson's Sparrow

Saltmarsh Sparrow


Figure 18. Mean blood Hg level (ppm) by songbird foraging guild as defined by De Graaf et

al. (1985).

Among songbirds sampled in New England and the Mid-Atlantic States, insectivores and

ground-feeding species, particularly those feeding in wetland habitats, had the greatest

blood Hg levels (Figure 18). As discussed previously, Saltmarsh, Nelson’s and Seaside

Sparrows (omnivore ground), Rusty Blackbird (insectivore ground), and Yellow Palm

Warbler (Dendroica palmarum) (insectivore ground) exhibited high blood Hg levels and

largely drove the trends observed in those guilds (Figures 19 & 20). Red-winged

Blackbirds (N = 40) are omnivore ground feeders with moderately high Hg blood levels;

they were primarily sampled in southern NY (Bashakill WMA: x = 0.23 ± 0.09ppm, N = 12;

Bog Brook WMA: x = 0.25 ± 0.25 ppm, N = 2; and Mohonk Preserve: x = 0.08 ppm, N = 1),

Southwest VA (two locations on Holston River: x = 0.20 ± 0.29 ppm, N = 16), and coastal ME

(Crane Pond WMA: x = 0.39 ± 0.30 ppm, N = 7).

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Blo

od

Hg

Leve

l (p

pm

, ww

)

Songbird Foraging Guilds


Mean + SD



concentrations in “omnivore ground” foraging guild species sampled in New England and

Mid-Atlantic States, 2000 to 2007.

Figure 20. Mean plus standard deviation and maximum level detected of blood Hg concentrations in “insectivore ground” foraging guild species sampled in New England and the Mid-Atlantic States, 2004 to 2010.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Blo

od

Hg

Leve

l (p

pm

, ww

)

Omnivore Ground Foraging Guild


Mean + SD

0

0.5

1

1.5

2

2.5

Blo

od

Hg

Leve

l (p

pm

, ww

)

Insectivore Ground Foraging Guild


Mean + SD


In upland habitats, Wood Thrushes were omnivore ground feeders that frequently

exhibited high blood Hg levels. BRI collected Wood Thrush blood and soil samples from the

Institute for Ecosystem Studies in Millbrook, NY. We compared blood Hg levels in the

ground-foraging wood thrush with soil Hg and Ca concentrations to determine correlations

between these variables.

5.3.3.1 CASE STUDY # 5 - RELATIONSHIP

BETWEEN SOIL Hg AND A GROUND-FORAGING

SONGBIRD: THE WOOD THRUSH

The Wood Thrush is a songbird of the eastern

US found in hardwood forests consisting of a

high canopy, dense understory, and thick leaf

litter layer. While it is generally considered a

common species, it has suffered recent

significant range wide declines of –1.7% per

year across its range (Sauer et al. 2008). In

New England, it is declining at –2 to –3% per

year and up to –4.4% per year in the

Adirondack Mts, NY (Sauer et al. 2008). The 2nd

New York Breeding Bird Atlas documented a –7.0% decline in Wood Thrush

occupancy between 1985 and 2005; the majority of those declines occurred in the

Adirondack Mts (Hames and Lowe 2008). They attributed winter habitat loss, over-winter

mortality, acid rain, and mercury deposition as the mostly likely contributors to the loss of

wood thrush populations. Hames et al. (2002) found that the probability of occupancy of a

site by breeding Wood Thrushes decreased with increasing acid rain deposition, which was

further compounded in low pH soils. Hames et al. (2006) found that soil pH was highly

significantly and positively related to the abundance of calcium-rich invertebrates, i.e.,

myriapods, isopods, and slugs. They also found that soil calcium was proportional to soil

pH and they postulated that absences of breeding wood thrushes was related to the

decreased availability of calcium-rich invertebrate prey items associated with acidified

soils.

We examined the relationship between soil Hg and available Ca in soils with blood Hg

levels in Wood Thrushes during the breeding season. We measured multiple soil

characteristics of organic and mineral layer soil samples collected at the Institute for

Ecosystem Studies in Millbrook, NY (see soil section for complete analysis). We measured

blood Hg levels of Wood Thrushes (N = 5) occupying the same soil sampling locations.

Wood Thrush blood Hg levels were highest at sites with high soil Hg and low exchangeable

Photo by Steve Maslowski/USFWS


Ca levels. There was an inverse relationship between blood Hg and exchangeable Ca levels

and a positive relationship between blood Hg and soil Hg levels (Figures 21 & 22).

Figure 21. Relationship between the amount of exchangeable calcium in the organic and

mineral soil layer and Wood Thrush (N = 6) blood Hg concentrations. Small sample size

precludes statistical reliability; however, preliminary analysis indicates: organic soil: R2=

0.55; mineral soil layer: R2 = – 0.67).

Figure 22. The relationship between the amount of exchangeable Ca in the organic and

mineral soil layers and blood Hg concentrations of Wood Thrushes (N = 6). Small sample

size precludes statistical reliability; however, preliminary analysis indicates: organic soil

layer: R2 = – 0.45; mineral soil layer: R2 = – 0.67.

0.00

0.05

0.10

0.15

0.20

80 100 120 140 160 180

WO

TH B

loo

d H

g (µ

g/g)

, ww

Soil Layer Hg (µg/kg), ww

Organic

Mineral

0.00

0.05

0.10

0.15

0 2 4 6 8 10 12

WO

TH B

loo

d H

g (p

pm

), w

w

Soil Exchangeable Ca

Mineral

Organic


The effects of calcium deficiency on birds can be species and even population specific

(Mand and Tilgar 2003). Subtle differences in food web pathways for MeHg

biomagnification and transfer can also create multiple-fold differences in blood Hg

exposure in sibling species within the same areas (Shriver et al. 2006). Since the Wood

Thrush feeds primarily on the forest floor by moving leaf litter to locate prey items

(Holmes and Robinson 1988), the pathway of MeHg through its prey is likely connected

with the organic soil. This analysis indicates that the Wood Thrush is a valuable choice as

an indicator species when linking abiotic and biotic compartments of Hg with Ca.

The omnivore lower-canopy guild was comprised mostly of Indigo Buntings (N = 11)

discussed above in the regional comparisons section. The insectivore air foraging guild is

limited to flycatchers (Tyrannidae) and swallows (Hirundinidae) (Figure 23). Tyrannidae

species had the highest blood Hg levels and are discussed in greater detail below in the

family comparisons section. Cliff Swallows (Petrochelidon pyrrhonota) were sampled in

riparian habitat within western and northern Maine ( = 0.21 ± 0.09 ppm; max = 0.47

ppm). They are diurnal foragers and group feed on swarms of insects; the types of insects

taken tend to reflect local availability and vary widely. Barn Swallows (Hirundo rustica)

and Tree Swallows (Tachycineta bicolor) have a similar diet to the Cliff Swallow; common

food items taken by these species include Homopterans, Dipterans, Hymenopterans,

Coleopterans, Ephemeropterans, Hemipterans, Lepidopterans, Orthopterans, and Odonates

(Robertson et al. 1992, Brown and Brown 1999). Swallow species that forage over open

water on emergent aquatic species are at increased risk of exposure to the MeHg that is

prevalent in aquatic ecosystems of northeastern US.

Omnivore ground/lower-canopy feeders ranged widely in their blood Hg levels; species

with the highest levels included Bicknell’s Thrush (Catharus bicknelli) and Song Sparrow

(Melospiza melodia) (Figure 24). Bicknell’s Thrush is exposed to high Hg levels in their

montane habitat and is discussed in greater detail in Case Study #6. Song Sparrows were

sampled in 11 regions in relatively low numbers, with the exception of southwest VA (N =

75) where mean blood Hg was 0.13 ± 0.09 ppm and the maximum level detected was 0.37

ppm. Song Sparrows tend to occupy shrubby areas along streams, marsh, or coastline but

will utilize a wide range of habitats (Arcese et al. 2002). Their breeding season diet is

primarily comprised of animal matter, of which they feed on a wide variety of taxa that

tends to vary by ecoregion (Aldrich 1984). Their diet and foraging locations make Song

Sparrows excellent bioindicators of Hg exposure risk in scrub-shrub zones adjacent to

aquatic habitats.



concentrations among “insectivore air” foraging guild species sampled in New England and

Mid-Atlantic States, 2005 to 2007.


concentrations in “omnivore ground/lower-canopy” foraging guild species sampled in New

England and Mid-Atlantic States, 1999 to 2007.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Blo

od

Hg

Leve

l (p

pm

, ww

)

Insectivore Air Foraging Guild


Mean + SD

0.0

0.2

0.4

0.6

0.8

1.0

Blo

od

Hg

Leve

l (p

m, w

w)

Omnivore Ground/Lower-Canopy


Mean + SD


Insectivore upper-canopy feeders tended to have low blood Hg levels with the exception of

several Red-eyed Vireo (Vireo olivaceus) and Yellow-throated Vireo (Setophaga dominica)

individuals (Figure 25). Red-eyed Vireo maximum blood Hg levels ranged widely by

sampling location; the lowest maximum level detected was 0.03 ppm at George L. Darey

Housatonic Valley WMA in western MA and the highest was 0.51 ppm along the Holston

River in southwest VA. High levels were also observed at: Witch Hole Pond in Acadia

National Park in coastal ME (0.43 ppm); Elk Lake (0.35 ppm), Dome Island, Lake George

(0.27 ppm), and Arbutus Lake (0.25 ppm) in the Adirondack Mts, NY; a residential

neighborhood in Standish, ME (0.30 ppm); and Tott’s Gap (0.29 ppm) in PA . Two Yellow-

throated Vireos were sampled; one sampled along the Holston River in Southwest VA had

relatively low blood Hg (0.07 ppm) and the other sampled at Bashakill WMA in southern

NY had a high blood Hg of 0.72 ppm. Major food items eaten by these species include

Lepidopterans, Dipterans, Coleopterans, Hemipterans, Homopterans and Hymenopterans;

less frequently they consume Orthopterans, Odonates, Arachnids, and Mollusks (Cimprich

et al. 2000). High blood Hg levels observed in individual vireos likely represent differences

in site contamination but also differences in foraging locations and food items eaten by

individuals. Individuals that consume greater quantities of spiders and other carnivorous

invertebrates are at greater risk of MeHg exposure.


concentrations in “insectivore upper-canopy” foraging guild species sampled in New

England and the Mid-Atlantic States, 1999 to 2010.

0.0

0.2

0.4

0.6

0.8

1.0

Blo

od

Hg

Leve

l (p

pm

, ww

)

Insectivore Upper-Canopy


Mean + SD


The Northern and Louisiana Waterthrushes are closely related warbler species with

overlapping ranges and habitats and they fill a unique role in the eastern US as “freshwater

shoreline foragers” (De Graaf et al. 1985). The Northern Waterthrush (Parkesia

noveboracensis) breeds from Alaska and much of Canada south to the northern U.S, and the

Louisiana Waterthrush (Parkesia motacilla) breeds from Minnesota, southern Ontario and

central New England south to Texas and Georgia. Both can be found in mixed forests, but

Northern Waterthrush is typically associated with coniferous woods containing swamps,

bogs, lakes, and willow/alder-bordered rivers. In contrast, Louisiana Waterthrush habitat

is more often deciduous cover near swift-moving brooks on hillsides, river swamps, and

along sluggish streams. Both species’ diets include a high biomass of aquatic prey (Craig

1984). Both forage at water’s edge for the following insect families: Chironomids,

Coleopterans, Diplopods, Ephemeropterans, Hemipterans, Neuropterans, Plecopterans,

Stratiomyiids, Tipulids, and Trichopterans (Robinson 1995). Additional prey includes

snails and other mollusks, arachnids, amphibians, and small fish. These prey items likely

explain their relatively high Hg body burdens (Figure 26).

The effects these body burdens may have on Louisiana Waterthrush are of particular

interest because it is a neotropical migrant of high conservation concern (Rich et al. 2004).

Indeed, comparisons of New York’s Breeding Bird Atlas data for the first (1980-1985) and

second (2000-2004) periods indicate a substantial – 21% loss of breeding records

(Rosenbeg 2008). Mulvihill et al. (2008) compared breeding Louisiana Waterthrush

territories along an acidified stream and a circumneutral stream and found that birds along

the acidified streams were generally young, inexperienced birds and that they exhibited

lower breeding density, later first laying dates, lower site fidelity, and traveled further

when foraging for food. Stream acidity did not appear to have an effect on nest success or

fecundity; however, the number of young fledged was twice as high on circumneutral

streams. Methylmercury availability and its effects on insectivorous passerines require

further investigation, but based on limited data, Louisiana and Northern Waterthrushes

may be at greatest risk among that feeding guild in riverine systems.



concentrations in Louisiana Waterthrush and Northern Waterthrush sampled in New


Elevated blood Hg levels of insectivore lower-canopy feeding species were primarily

observed in Carolina Wrens (Thryothorus ludovicianus) and several warblers (Figure 27).

These included: Common Yellowthroats (Geothlypis trichas) at Ferd’s Bog (0.31 ppm) and

Spring Pond Bog (0.33 ppm) in the Adirondack Mts, NY, Crane Pond WMA (0.24 ppm) in

coastal MA, and Great Swamp WMA (0.41 ppm) in southern NY; Magnolia Warbler

(Dendroica magnolia)at Arbutus Lake (0.22 ppm) in the Adirondack Mts, NY; and Myrtle

Warbler (Dendroica coronata) at Spring Pond Bog (0.32 ppm) in the Adirondacks Mts, NY

and along the East Kennebago River (0.16 ppm) in western ME. Insectivore bark/upper-

canopy foraging guild was comprised of two Yellow-throated Warblers (Setophaga

dominica) sampled along the Holston River in Southwest VA ( = 0.26 ± 0.20 ppm; max =

0.41 ppm). Insectivore marsh foraging guild consisted of two Marsh Wrens (Cistothorus

palustris) sampled at McKinney NWR in coastal CT ( = 0.25 ± 0.003 ppm). Marsh Wrens

feed primarily on insects and spiders at or near the surface of the water in freshwater,

saltwater, and brackish marshes (Kroodsma and Verner 1997). In the New England and

Mid-Atlantic Coast, Marsh Wrens declined at a significant annual rate of -2.9% between

1966 and 2009. Although our small sample size limits speculation on whether Marsh Wren

populations are being affected by high levels of Hg, further research to determine the

effects of blood Hg on the reproductive success of Marsh Wrens in this region is warranted

given the nature of their diet and habitat.

0.0

0.2

0.4

0.6

0.8

1.0

PA

(N

= 4

)

Cat

skill

Mts

, NY

(N

= 4

)

Ce

ntr

al/W

est

ern

NY

(N

= 3

)

Sou

thw

est

VA

(N

= 7

)

Sou

the

rn N

Y (

N =

2)

No

rth

ern

ME

(N =

1)

Sou

the

rn N

Y (

N =

5)

Louisiana Waterthrush Northern Waterthrush

Blo

od

Hg

(pp

m),

ww


Mean + SD



concentrations in “insectivore lower-canopy” foraging guild species sampled in New


Blood Hg levels in the remaining foraging guilds were generally low. The highest levels

observed in insectivore bark foraging guild was in a White-breasted Nuthatch (Sitta

carolinensis) (0.24 ppm) sampled along the Holston River in Southwest VA and a Red-

breasted Nuthatch (Sitta canadensis) (0.14 ppm) sampled in Spring Pond Bog in the

Adirondack Mts, NY. The omnivore/vermivore ground/lower-canopy foraging guild is

comprised solely of the American Robin (Turdis migratorius), whose maximum blood Hg

levels were found along the Holston River in southwest VA (0.19 ppm) and in a residential

neighborhood in southern Maine (0.15 ppm). The insectivore air/lower canopy foraging

guild consisted of American Redstart (Setophaga ruticilla) and Hooded Warbler (Wilsonia

citrina). American Redstart sample size and blood Hg levels were low; however, one

individual sampled in Black Rock Forest in Southern NY had a blood Hg level of 0.19 ppm.

Likewise, Hooded Warbler sample sizes were low and so were blood Hg levels; however,

one individual sampled in Allegany State Park in Central/Western NY had a blood Hg level

of 0.18 ppm. Blood Hg levels were negligible in the last two foraging guilds, frugivore

upper-canopy and omnivore upper-canopy; however, sample sizes were very small.

Frugivore upper-canopy foraging guild consisted of Cedar Waxwings sampled along the

0.0

0.2

0.4

0.6

0.8

1.0

Blo

od

Hg

(pp

m),

ww

Insectivore Lower-Canopy


Mean + SD


Holston River in Southwest VA and one Rose-breasted Grosbeak sampled in Devil’s

Tombstone in the Catskill Mts, NY made up the omnivore upper-canopy foraging guild.

5.3.4 MERCURY EXPOSURE BY FAMILY

Regional and foraging guild analyses indicated that many of the species with the highest

blood Hg levels were closely-related, e.g., coastal sparrows and Rusty and Red-winged

Blackbirds. These results warranted further examination of family groupings to determine

whether certain genera were prone to Hg biomagnifications. Indeed, the Emberizidae and

Icteridae families had the highest means (Figure 28), with members associated with

wetlands exhibiting greater levels than their upland relatives. For example, the coastal

sparrows and the Swamp Sparrow (Melospiza georgiana) ( = 0.43 ± 0.36) had the highest

levels among the Emberizids (Appendix B). Similar patterns are apparent in the Icteridae,

Parulidae, and Troglodytidae family groups (Appendix B).


concentrations among songbird families sampled in New England and Mid-Atlantic States,

1999 to 2010.

Tyrannidae, the flycatchers, had the third highest mean Hg blood levels among the family

groups. They are part of the insectivorous air foraging guild and feed on a wide range of

invertebrate species. Two Eastern Wood-Pewees (Contopus virens) sampled near Great

Swamp WMA in southern NY had the highest mean blood Hg levels (Figure 29). Traill’s

Flycatchers (Willow/Alder flycatcher) in the Adirondack Mts, NY and Acadian Flycatchers

along the Holston River in Southwest VA had the highest blood Hg levels among flycatchers

in those sampling regions, = 0.36 ± 0.24 (N = 4) and = 0.29 ± 0.13 (N = 12), respectively.

Traill’s Flycatchers are generally found in shrubby wetlands and Acadian Flycatcher

0.0

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1.0

1.5

2.0

2.5

3.0

3.5

4.0

Me

an B

loo

d H

g (p

pm

, ww

) Maximum Level Detected Mean + SD


(Empidonax virescens) habitat is riparian forests. Due to their aquatic ecosystem

associations, it is not surprising to find elevated blood Hg levels, particularly within known

mercury hotspots.


concentrations in Tyrannidae species sampled in New England and Mid-Atlantic States,

2005 to 2007.

The Eastern Wood-Pewee, on the other hand, is a relatively common songbird associated

with open forests that forages in the middle section of the understory up to the lower

canopy. Our sample size was very low, however, the blood Hg levels in the individuals we

sampled were very high indicating that Eastern Wood-Pewees are capable of accumulating

deleterious Hg concentrations from its diet. Typically, their diets consists of small, flying

insects, including Dipterans, Homopterans, Lepidopterans, Hymenopterans, Coleopterans,

Orthopterans, Plecopterans, and Ephemopterans (McCarty 1996). The two individuals we

sampled were in Great Swamp WMA, which is a red maple swamp in Southern NY. While

the Eastern Wood-Pewee is not listed as a species of special concern anywhere, its

populations are decreasing across its range at a significant rate of –1.7% per year (Sauer et

al. 2008). Within our study area, annual significant declines approach –3% to –4% in

sections of New York and New England and up to –7.4% in the Blue Ridge Mountains of

Virginia (Sauer et al. 2008). The 2nd New York Breeding Bird Atlas noted that while the

species was still a common and widespread bird, it was disappearing from sites with

marginal habitat which is generally where populations changes are first detected

(McGowan 2008). It listed potential causes for this decline as maturation of forests in the

northeast and changes on the wintering grounds in northern South America.

0.0

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0.8

1.0

1.2

1.4 B

loo

d H

g Le

vel (

pp

m, w

w)

Tyrannidae

Maximum Species Level Detected

Mean + SD


Hg contamination may be a co-stressor to species facing population declines due to habitat

loss and degradation. The Great Swamp WMA provides much-needed hardwood swamp

habitat for a variety of songbird species; however, two types of invertebrate prey, ground

beetles (Carabidae) and Long-jawed Orb Weavers (Tetragnathidae), sampled at this site

had elevated total MeHg levels: = 0.08 ppm, dw (N = 2) and = 0.10 ppm, dw (N = 2),

respectively. Additional samples are necessary to draw a clear connection between

available Hg in prey and blood Hg levels in songbirds at this site, but it should be noted that

three songbird species sampled here (Common Yellowthroat, Song Sparrow, and Wood

Thrush) exhibited blood Hg levels that were twice as high as the overall species’ mean

blood level detected across their sampling range.

The degree of Hg exposure among species is correlated with trophic position and MeHg

availability (Evers et al. 2005). For closely-related species that occupy similar trophic

positions, there are several factors that determine each species’ degree of MeHg exposure,

including: geographic area, foraging guild, and habitat type. Members of the thrush family,

Turdidae, illustrate how differences in habitat and microhabitat can affect blood Hg levels

among closely-related species occupying similar foraging guilds within the same

geographic area. In the case of the Bicknell’s Thrush, we see the additive effects.

5.3.4.1 SONGBIRD CASE STUDY #6 - BICKNELL’S THRUSH

The Bicknell’s Thrush is relegated to breeding in subalpine areas of conifer-dominated

forests with elevation thresholds that are latitudinally controlled (Lambert et al. 2005); in

the U.S., lowest elevations occupied are in northern Maine at 750m, while in the

southernmost extent of its range in the Catskill Mountains the Bicknell’s Thrush generally

breeds on mountains 1,100 m or higher (Rimmer et al. 2001). Montane habitats in the

Northeast are subjected 2-5× higher Hg input than surrounding low elevation habitats

(Miller et al. 2005). Cloud and fog water can directly deposit pollutants onto the high

elevation landscapes they come into contact with, and furthermore, the topographical

features of mountains enhance precipitation rates (as indicated by Rimmer et al. 2005).

These factors appear to contribute to high levels of Hg deposition. Additionally, the thin,

sandy mountaintop soils in the northeastern US have low calcite levels, and thus, low

buffering capacity from acidic input, such as sulfuric and nitric acids, resulting in lower soil

pH (Driscoll et al. 2001). Therefore, these soils are often more acidic than lower elevation

soils containing highly buffered, thick organic soil layers (Bernard et al. 2009). As we

discussed previously in the soil section, acidified soils can have multiple ramifications on

songbirds. The ability of Hg to methylate in dry soils are unclear, but Rimmer et al.’s

(2010) study of a montane food webs documented an increasing trend in MeHg levels with

increasing trophic level. Based on these findings, it appears that high elevation forests


species, such as the Bicknell’s Thrush, should have proportionally higher Hg levels than its

relatives occupying similar niches in low elevation forests. Indeed, we compared thrush

blood Hg levels and found that Bicknell’s Thrush had significantly higher levels than all

other thrush species (P ≤ 0.05) (Figure 30). Rimmer et al. (2005) stated that Bicknell’s

Thrush was a useful bioindicator of MeHg in high-elevation fir-dominated forests. We

focused on sampling Bicknell’s Thrush in montane habitats throughout the northeastern US

to determine geographic differences in blood levels (Figure 31), but we found no significant

differences.

Figure 30. Mean blood Hg concentration in Turdidae family species sampled in New

England and Mid-Atlantic States, 1999 – 2008. Bicknell’s Thrush blood Hg levels were

significantly higher than all other thrush species (P ≤ 0.05).

The habitat of the Bicknell’s Thrush places it at higher risk of Hg exposure than other

thrush species; however, the threat of Hg exposure in those species is no less significant.

Among thrushes found in the northeastern US, the Eastern Bluebird (Sialia sialis) likely has

the lowest Hg exposure risk due to a largely frugivore diet and old field habitat. The

remaining thrushes are generally categorized as ground-foraging omnivores, although

some also feed in the lower canopy. Holmes and Robinson (1988) found that in northern

hardwood forests where habitat and range overlapped for several thrush species, they

partitioned available resources by occupying different macrohabitat, microhabitat, prey-

attack methods, and diet. Wood Thrush, Veery (Catharus fuscescens) , Swainson’s Thrush

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1.0

Blo

od

Hg

Leve

l (p

pm

, ww

)

Turdidae


Mean + SD


(Catharus ustulatus) , and Hermit Thrush (Catharus guttatus) fed frequently on the ground;

however, Wood Thrush fed almost exclusively on the ground while the others also fed in

the sapling, subcanopy, and, occasionally, the canopy. The Swainson’s Thrush utilized the

canopy most often and focused 10% of its prey attacks in that foliage stratum. The

majority of our Swainson’s Thrush samples were obtained at many of the same sites as the

Bicknell’s Thrush samples, yet the Swainson’s Thrush had significantly lower blood Hg

levels. Typically, Hg concentrations in the leaf litter are higher than levels in the live foliage

(Rimmer et al. 2010). If indeed certain thrush species or individuals spend more time

foraging in the live foliage, they may be exposed to less Hg than thrushes that feed almost

exclusively in the leaf litter layer, such as the Wood Thrush and Bicknell’s Thrush. These

characteristics make Bicknell’s Thrush an excellent indicator species of available Hg in the

leaf litter layer for high elevation sites, whereas the Wood Thrush appears to be an

excellent indicator in low elevation forest sites, particularly those adjacent to rivers and

wetlands.

Figure 31. Regional means plus standard deviations and maximum levels detected of blood

Hg concentrations Bicknell’s Thrush sampled in New England and New York, 1999 – 2007.

5.3.5 BLOOD MERCURY CONCENTRATIONS AND REPRODUCTIVE SUCCESS

Survival, reproduction, immune response, song, and endocrine function are all aspects of

songbird ecology that may be adversely affected by elevated blood Hg levels (Hallinger et

al. 2010, Brasso and Cristol 2008, Hawley et al. 2009, and Wada et al. 2009). Brasso and

Cristol (2008) studied Tree Swallows along the South River in Virginia and found that

second-year birds along a polluted section of river produced fewer chicks than those in the

uncontaminated reference area. There was a significant and positive relationship between

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1.0

Blo

od

Hg

Leve

l (p

pm

, ww

)

Bicknell's Thrush Sampling Areas

Maximum Level Detected Mean + SD


female tree swallow blood mercury levels and the average mercury levels of eggs (Brasso

et al. 2010). Adult female birds depurate some of their Hg body burden during the egg-

laying process as it is deposited into the albumen, shell, and yolk (Kennamer et al. 2005).

The percentage of Tree Swallow eggs that survived to produce a fledgling was significantly

lower at the contaminated site compared to the reference site (Brasso and Cristol 2008).

However, they were unable to predict nest success based on the female’s blood Hg

concentration. Recently, BRI recently conducted research to assess reproductive success

of a terrestrial forest invertivore, the Carolina Wren (Thryothorus ludovicianus) and

successfully developed effects concentrations based on their findings, which are

highlighted in Case Study # 7.

5.3.5.1 SONGBIRD CASE STUDY # 7 - CAROLINA WREN

(JACKSON ET AL. 2011)

Carolina Wren nest boxes were monitored for nest

success along known contaminated sections of the

South River and North Fork Holston River in

Virginia and along several nearby uncontaminated

reference rivers. Carolina Wrens near the

contaminated sites showed blood Hg levels that

were 7 to 10 times higher than reference site birds.

Additionally, those individuals at contaminated sites

had 34% reduced reproductive success compared to

those at reference sites. Female blood Hg

concentration was a good predictor of overall nest

success; birds with higher Hg body burdens were less

likely to successfully fledge young. Jackson et al. (2011) documents Hg effects

concentrations in blood, feathers and eggs for Carolina Wrens that corresponds with range

of reduced nest success (Table 1). According to the 10% nest reduction effects

concentration, it appears that 12 of the 82 songbird species we sampled had individuals

with blood Hg levels that put them at risk of reduced nest success (Figure 32).

Photo provided by BRI staff


Table 1. Carolina Wren blood, feather, and egg Hg effects concentrations associated with MCestimate-modeling reduction in nest success (adapted from Jackson et al. 2011).

Figure 32. Songbird species sampled in New England and the Mid-Atlantic States between

1999 and 2010 with individuals whose blood Hg (ppm, ww) concentrations put them at

risk of reduced nesting success. Risk categories associated with 10% (0.7 ppm), 20% (1.2

ppm), 30% (1.7 ppm) reduced nesting success are based on Jackson et al.’s (2011) Carolina

Wren research. *Indicates neotropical migrant species.

0.0

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1.5

2.0

2.5

3.0

3.5

4.0

Blo

od

Hg

Leve

l (p

pm

, ww

) Maximum Species Level Detected

Species Mean + Standard Deviation

- 30% reduced nest success

- 20%

- 10%

Mercury Risk Categories

Reduction in Nest Success

Blood Hg (ppm, ww)

Body Feather Hg (ppm, fw)

Tail Feather Hg (ppm, fw)

Egg Hg (ppm, ww)

Low 10% 0.7 2.4 3.0 0.11

Moderate 20% 1.2 3.4 4.7 0.20

High 30% 1.7 4.5 6.4 0.29

Very High

40% 2.1 5.3 7.7 0.36

50% 2.5 6.2 9.1 0.43

60% 2.9 7.1 10.4 0.50

70% 3.3 7.9 11.8 0.57

80% 3.8 9.0 13.5 0.66

90% 4.4 10.3 15.5 0.76

99% 5.6 12.8 19.5 0.97


5.4 CONCLUSIONS

There are compelling reasons to be concerned about the effects of airborne pollutants on

breeding songbirds in eastern forests. Much is already known about the effects of acidic

deposition on northeastern landscapes and the depletion of available Ca in soil, but only

recently has acidification also been implicated in increased MeHg availability. The

distribution of Hg and the availability of MeHg are now well documented in the Northeast.

Detection of this pattern was accomplished through a four-year study funded by the USDA

Forest Service. BRI and their collaborators compiled and synthesized most of the publicly

available mercury data in the Northeast into a series of 21 papers in a special issue of

Ecotoxicology (Evers and Clair 2005). From this comprehensive review on how Hg is

distributed across the landscape, three findings emerged that partly serve as a basis for this

current investigation: (1) new findings indicate MeHg availability is more prevalent in

terrestrial birds than previously considered (Evers et al. 2005); (2) birds in montane

terrestrial habitats may be at risk (Rimmer et al. 2005), likely as a consequence of a higher

rate of atmospheric deposition of wet and dry Hg than in lower elevation habitats

(VanArsdale et al. 2005); and (3) there is a significant relationship between wet and dry Hg

deposition models based on Miller et al. (2005) and on Bicknell’s Thrush blood Hg levels

(Rimmer et al. 2005). The comprehensive sampling effort of songbirds discussed in this

report revealed elevated blood Hg levels, and in some areas, above levels of concern.

Patterns of blood Hg levels indicate that body size, habitat type, elevation, and geographic

location are important variables to measure. Some species, such as the Saltmarsh Sparrow,

Rusty Blackbird, and Louisiana Waterthrush appeared to bioaccumulate greater amounts

of MeHg than other species and are experiencing declines in population size.

As electric utilities are the major sources of atmospheric Hg in the U.S., results from this

investigation provide important information to policy makers on the pervasiveness of Hg in

the Northeast and how synergy with other stressors such as acidic deposition could have

broad-scale impacts to bird populations and ecosystem health. If future efforts link

emission sources from the Ohio River Valley with biological Hg hotspots in New England

and Mid-Atlantic States, the need for implementation of the Mercury and Air Toxics

Standards (MATS) Rule by the U.S. Environmental Protection Agency is even more

compelling (U.S. EPA 2011). No individual point source in New England, New York, or New

Jersey releases more than 500 pounds of Hg per year, while several sources in

Pennsylvania and Ohio exceed this annual rate of release. Continued research could

ultimately contribute to a framework for new national legislation to regulate Hg emissions

and standardize monitoring efforts. Should the decline of songbirds truly signal a

widespread and major disruption in how forests function in New England and the Mid-

Atlantic region, then this effort is very timely to better define potential sources of declines

in songbird populations.


6.0 BATS

6.1 STUDY AREA

Bat capture and sampling occurred in multiple territory locations at 44 sites distributed

across 7 New England and Mid-Atlantic States (Figure 33).

6.2 METHODS

Single, double, and triple high mist nets were strung directly in front of ledge outcroppings,

between trees along small access roads, or in the middle of rivers to funnel bats into nets.

Using the assumption that bats fly to water for drinking and feeding purposes after leaving

daytime roosts, roads that led towards water were chosen. Nets were set at dusk and

monitored until at least 2300 hours; if bats were being captured, nets were left open until

0100 hours. All bats captured were identified to species, checked for reproductive status,

sexed, and aged. Fur samples were cut from the back and abdomen collected with clean

stainless steel scissors and collected into ziplock bags. Total mercury (THg) concentrations

are reported as parts per million fresh weight (ppm, ww). The percent methylmercury

(MeHg) present in bat fur is not known; however, Porcell (2004) found that 90% or greater

of THg in raccoon hair was MeHg. All bats were released unharmed at the site.


6.3.1 SPECIES MERCURY EXPOSURE

We sampled 802 bats representing 13 species between 2006 and 2008. Adult fur Hg levels

ranged from 0.69 ppm in a Red Bat (Lasiurus borealis) sampled in Monongahela National

Forest in WV to 120.31 ppm in a Big Brown Bat (Eptesicus fuscus) sampled along the Little

River in NH. Juvenile fur Hg levels ranged from 0.29 ppm in a Little Brown Bat (Myotis

lucifugus) sampled along Middle River in VA to 18.83 ppm in a Little Brown Bat sampled in


Scarborough Marsh in coastal ME. Big Brown Bat ( = 17.78 ± 22.18 ppm), Southeastern

Myotis (Myotis austroriparius) ( = 10.50 ± 9.33 ppm), Indiana Bat (Myotis sodalis) ( =

10.58 ± 5.07 ppm), and Evening Bat (Nycticeius humeralis) ( = 10.56 ± 7.99 ppm) had the

highest mean fur Hg concentrations (Figure 34).

Very few investigations have been conducted related to wild bats’ exposure to heavy

metals in the environment. Baron et al. (1999) completed a risk assessment for aerial

insectivorous wildlife on the Clinch River, TN (Oak Ridge Reservation). Using a model, they

determined the dose levels for the NOAEL and LOAEL for little brown bats to be 0.11 and

0.56 ppm, respectively. Bats experiencing exposure equal or greater than the LOAEL were

found to display impaired growth, reproduction, and offspring viability (Verschuuren et al.

1976). All of our Little Brown Bat samples, which ranged from 0.29 to 35.00 ppm,

exceeded the NOAEL of 0.11 ppm and 90% had levels that exceeded the LOAEL of 0.56

ppm. Burton et al. (1977) found that mice with fur Hg concentrations of 7.8 ppm (fw) and

10.8 ppm (fw) showed behavioral deviations including decreased ambulatory activity and

stress tolerance, and decreased swimming ability, respectively. New data on

neurochemical markers in Little Brown Bats indicates that 10 ppm in the fur is a

preliminary subclinical threshold, above which researchers have shown changes to bat

neurochemistry (Nam et al. 2012). With the exception of Hoary Bat and Seminole Bat, every

bat species we sampled had individuals with fur Hg levels that exceeded the level of

concern (10 ppm) and 15% (n = 124) of our total sample exceeded that level.


Figure 33. Study area of bat sampling locations.


Figure 34. Mean plus standard deviation and maximum level detected of fur Hg

concentrations in bat species sampled in New England and Mid-Atlantic States, 2006 to

2008. Red line indicates a preliminary subclinical threshold for mercury exposure in bats

(10 ppm in fur of Little Brown Bats), above which researchers have shown changes to their

neurochemistry (Nam et al. 2012).

6.3.2 REGIONAL MERCURY EXPOSURE

Bats sampled at Little River in Southeastern NH had the highest mean fur Hg

concentrations ( = 33.96 ± 37.12 ppm), due to extremely high levels in Big Brown Bats (

= 53.48 ± 42.04 ppm) (Figure 35 & 36). Pollution levels in the Little River are known to be

high in this area and the US Attorney’s Office has filed complaints on behalf of the U.S.

Environmental Protection Agency (EPA) against at least two industrial plants in the area

for violations of the Clean Water Act (U.S. EPA 2010).

0

20

40

60

80

100

120

140 Fu

r H

g (p

pm

, ww

)

Bats Species


Mean + SD


Figure 35. Regional mean fur Hg concentrations in bats sampled in New England and Mid-Atlantic States, 2006 to 2008.

0

20

40

60

80

100

120

140

Fur

Hg

Leve

l (p

pm

, ww

)

Bat Sampling Areas


Mean + SD

0

20

40

60

80

100

120

140

Fur

Hg

Leve

l (p

pm

, ww

)

Bat Species Sampled in Southeastern NH


Mean + SD


Figure 36. Mean and maximum level detected of fur Hg (ppm) in bats sampled near Little River, Rockingham County in Southeastern NH, 2008.

Big Brown Bat fur Hg concentrations were also elevated in other regions where sampled,

particularly Coastal VA and Central/Western NY ( = 15.97 ± 15.62 ppm and = 22.47 ±

13.56, respectively) (Figure 37). Eastern Small-footed Myotis had the next highest mean

fur Hg level ( = 12.88 ± 4.98 ppm); however, the sample size is small (N = 7) and spread

out over 3 sampling regions (Figure 38). Indiana Bats (N = 12) sampled in Southern NY

and Central/Western NY had the next greatest mean fur Hg level ( = 10.58 ± 5.07 ppm)

(Figure 39). Indiana Bats are a federal and NYS-listed endangered species. They were first

identified as being in danger of extinction as far back as 1966 and were one of the first

mammals listed as endangered under the Endangered Species Act of 1973. Indiana Bats

have also been identified as a species vulnerable to population declines due to white-nose

syndrome (NYSDEC 2010).

Evening Bats (N = 39) sampled at Great Dismal Swamp in coastal VA had elevated mean fur

Hg concentrations ( = 10.56 ± 7.93 ppm, max = 40.90 ppm). Southeastern Myotis (N = 9),

also sampled at Great Dismal Swamp, had similar fur Hg levels ( = 10.50 ± 9.33 ppm, max

= 25.00 ppm). Silver-haired Bats (N = 7) sampled in WV had a mean fur Hg level of 9.33 ±

3.91 ppm with a maximum level detected of 14.23 ppm. Rafinesque’s Big-eared Bats (N =

4) sampled in Great Dismal Swamp in Coastal VA had a mean fur Hg level of 8.10 ± 3.38

ppm and a maximum level detected of 12.00 ppm. Northern Long-eared Bats (Myotis

septentrionalis) (N = 148) had an overall mean fur Hg concentration of 8.04 ± 6.58 ppm and

maximum level detected of 41.53 ppm. Those sampled in Central/Western NY had the

highest mean fur Hg concentrations ( = 16.89 ± 10.27 ppm, N = 19), which were

significantly greater than levels detected in Coastal ME, WV, and Southern NY (Figure 40).

Eastern Pipistrelles (N = 22) were sampled in Great Dismal Swamp in Coastal VA and WV

(Figure 41). Red Bats (N = 38) were primarily sampled at Great Dismal Swamp in Coastal

VA and Monongahela National Forest in WV (Figure 43); Coastal VA levels were higher ( =

5.55 ± 7.12 ppm) than WV ( = 4.46 ± 2.56 ppm) but the difference was not significant

(Figure 42). Red Bats were also sampled in Coastal ME and MA, Southern NY, and the

Adirondack Mts, NY but sample sizes were small.

Little Brown Bats (N = 441) had the highest mean fur Hg levels in southeastern NH ( =

11.70 ± 6.08 ppm, N = 5) followed by the Adirondack Mts, NY ( = 7.55 ± 6.61 ppm, N = 60),

and Coastal MA ( = 6.22 ± 4.23 ppm, N = 14) (Figure 43). Seminole Bats (N = 9) were

sampled in Great Dismal Swamp and had low fur Hg levels ( = 2.68 ± 0.76 ppm). One

Hoary Bat was sampled in Adirondack Park (1.63 ppm) and 5 were sampled in WV ( =

1.99 ± 0.93).


Figure 37. Regional mean fur Hg concentrations in Big Brown Bats sampled in New

England and Mid-Atantic States, 2006 to 2008. Big brown bats sampled in NH had

significantly higher fur Hg concentrations than Coastal VA, Southern NY, and WV (P < 0.05);

Adirondack Mts, NY was not included in analysis due to small sample size.

0

20

40

60

80

100

120

140

Fur

Hg

Leve

l (p

pm

, ww

)

Big Brown Bat Sampling Regions


Mean + SD

0

10

20

30

40

50

Fur

Hg

Leve

l (p

pm

, ww

)

Eastern Small-footed Myotis Sampling Regions

Maximum Value Detected

Mean + SD


Figure 38. Regional mean fur Hg concentrations in Eastern Small-footed Myotis sampled in

coastal ME, southern NY, and WV, 2006 to 2008. Small sample size precluded statistical

analysis.

Figure 39. Regional mean and maximum levels detected of fur Hg concentrations in

Indiana Bats sampled in New York State, 2006 to 2008.

Figure 40. Regional means and maximum levels detected of fur Hg in Northern Long-eared

Bats sampled in New England and Mid-Atlantic States, 2006 to 2008. Northern Long-eared

Bats in Central/Western NY had significantly higher fur Hg levels than those sampled in

0

10

20

30

40

50

Central/Western NY (N = 1) Southern NY (N = 11)

Fur

Hg

Leve

l (p

pm

, ww

)

Indiana Bat Sampling Regions


Mean + SD

0

10

20

30

40

50

Fur

Hg

Leve

l (p

pm

, ww

)

Northern Long-eared Bat Sampling Regions


Mean + SD


Coastal ME, WV, and Southern NY (P < 0.0001) (Southeast NH was excluded from analysis

due to small sample size).

Figure 41. Regional means and maximum levels detected of fur Hg concentrations in

Eastern Pipistrelles sampled in WV and Coastal VA, 2007 and 2008.

Figure 42. Regional means and maximum levels detected of fur Hg concentrations in Red

Bat sampled in New England and Mid-Atlantic States, 2006 to 2008. No significant

difference was detected in fur Hg levels between Coastal VA and WV; small sample size

precluded analysis of other regions.

0

10

20

30

40

50

WV (N = 13) Coastal VA (N = 9)

Fur

Hg

Leve

l (p

pm

, ww

)

Eastern Pipistrelle Sampling Regions


Mean + SD

0

10

20

30

40

50

Fur

Hg

Leve

l (p

pm

, ww

)

Red Bat Sampling Regions


Mean + SD


Figure 43. Regional means and maximum levels detected of fur Hg concentrations in Little

Brown Bats sampled in New England and Mid-Atlantic States, 2006 to 2008. Little Brown

Bats sampled in the Adirondack Mts, NY had significantly higher fur Hg levels than those

sampled in PA, WV, and Northwest VA (P < 0.05); Southeast NH had the highest mean but

was precluded from statistical analysis due to small sample size.

6.3.4 MERCURY EXPOSURE BY AGE AND SEX

Adult male bats (N = 213) had a mean fur Hg level of 9.82 ± 9.66 ppm, which was

significantly higher than the mean for juvenile males ( = 4.39 ± 3.42 ppm) and adult and

juvenile females ( = 6.71 ± 9.29 ppm and = 2.88 ± 2.46 ppm) (P < 0.0001) (Figure 44).

Adult female levels were significantly higher than both juvenile females and males (P <

0.02), while juvenile male levels were significantly higher than juvenile females (P <

0.0001). These results are similar to age and gender sensitivities detected in bats sampled

at Mammoth Cave National Park, KY (Webb et al. 2006); however, the maximum fur Hg

level detected in KY (10 ppm) was much less than in our samples.

Bats are long-lived species (10 to 30 years) and thus have the potential to accumulate high

levels of Hg over the course of a lifetime. However, it is impossible to distinguish and

classify ages beyond simply juvenile (less than 12 months) and adult. Therefore, it is

possible for fur Hg means for the adult age class to be skewed to the right due to a few very

old individuals. Females had lower Hg levels than males despite that they have higher

energy demands during the breeding season (i.e., milk production) and consequently

consume more insect matter during this period, thereby increasing their exposure to

mercury. This difference is likely a result of females transferring a portion of their Hg body

0

10

20

30

40

50

Fur

Hg

Leve

l (p

pm

. ww

)

Little Brown Bat Sampling Area


Mean + SD


burden to their young in the uterus and through breast milk, thus reducing their own Hg

levels in the process.

Figure 44. Mean fur Hg concentrations among male and female adult and juvenile bats

sampled in New England and the Mid-Atlantic States, 2006 to 2008. Adult male bats had

significantly higher (P < 0.0001) fur Hg levels than female adults and juveniles of both

sexes. Female adults were significantly higher than juveniles of both sexes (P < 0.02). Male

juveniles were higher than juvenile females (P < 0.0001).

6.4 CONCLUSIONS

Bat fur samples are indicators of Hg body burdens, reflecting both dietary uptake and body

accumulation (Mierle et al. 2000, Yates et al. 2005). Since adults live for decades, they

accumulate an overall body burden of Hg, whereas juveniles less than one year old have

only accumulated Hg levels from their mother’s milk and from the site where they have

foraged. Bats are at risk of Hg exposure from consumption of both aquatic and terrestrial

insects. However, bats may be exposed to levels of mercury high enough to cause sublethal

effects if they consume large quantities of insects that spend larval stages in contaminated

sediments (Hickey et al. 2001).

Our results demonstrate that bats are at great risk when feeding in riparian habitats.

Insectivorous bats use both aerial and gleaning techniques when foraging over river

surfaces and floodplain edges. Big Brown Bats with exceptionally high Hg levels in NH

were captured over a forested stream and were presumably feeding on aquatic insects.

Aquatic nymphs of flying insects with elevated Hg levels were the presumed source of Hg in

several aerial insectivores, including the Eastern Pipistrelle, along a point source-polluted

Virginia river (Powell 1983). In terrestrial ecosystems, bats consume a variety of insect

prey. Carter et al. (2003) found Northern Long-eared Bats main prey was Coleoptera and

0

2

4

6

8

10

12

14

16

18

20

Female Juvenile (N = 122)

Male Juvenile (N = 72)

Female Adult (N = 389)

Male Adult (N = 213)

Fur

Hg

(pp

m),

fw

Bat Sex and Age Class


Lepidoptera followed by Diptera, all of which have been shown in our study to accumulate

mercury. In Indiana and Illinois, small beetles were the major component of the diet of Big

Brown Bats (Whitaker 1995). Other studies found Northern Long-eared Bats and Little

Brown Bats typically preyed on moths and beetles, but overall had a varied diet including

spiders (Whitaker and Hamilton 1998, Brack and Whitaker 2001).

Spiders have been shown in our study and previous studies to have elevated Hg

concentrations (Adair et al. 2003, Cocking et al. 1991). Hg levels in Coleopterans (beetles)

are generally low, although its feeding behavior affects the degree of concentration. For

example, insectivorous invertebrates have been shown to accumulate MeHg at levels 8.5

times higher than herbivorous invertebrate species (Mason et al. 2000). However, the

degree of Hg contamination and where it is concentrated in the ecosystem will also affect

which species exhibit elevated MeHg levels. Larval Scarabaeidae beetles along a

contaminated river floodplain in Virginia had significantly higher MeHg concentrations

than larval Elateridae beetles (Cocking et al. 1991). Scarabaeidae feed on detritus, fungi,

roots, tubers, and underground plant parts while Elateridae consume roots and

underground stems, seedlings, and other low-trophic level insects (Peterson 1951).

Underground plant parts contained greater concentrations than above ground plants and

there was an abundance of Hg in soil-dwelling invertebrates at Cocking et al.’s (1991) study

site indicating that the detritus food web is a significant pathway for Hg bioaccumulation.

The effects of Hg in the aquatic and terrestrial food webs are detrimental to local bat

populations. Most bat species in our study exceeded levels shown to have adverse effects

in rodents across multiple regions, indicating that bats are at risk to Hg exposure in a

variety of prey items throughout the Northeast US. These trends are not unique to the

northeastern US. Hickey et al. (2001) examined fur Hg concentrations in various

Chiroptera species from eastern Ontario and adjacent Quebec, Canada. In 1997, they

pooled samples from five sites and found fur Hg concentrations ranging from 2.0 to 7.6

ppm, (fw). In 1998, they sampled the same sites and found fur Hg concentrations that

approached or exceeded 10.0 ppm (fw). Massa and Grippo (2000) examined various

Chiroptera species from rivers in Arkansas that were under fish consumption advisories

and found fur Hg concentrations ranging from 1.0 to 30 ppm, (fw). They concluded that Hg

accumulation had exceeded the hazard criteria set by the U.S. Fish & Wildlife Service and

that Hg accumulation in bats is a serious problem that warrants further investigation.

Fifteen percent of our sample exceeded the concentrations of concern for rodents (10.8

ppm) and 5 percent (N = 35) of our sample exceeded the level established for the much

larger mammals, mink and otter (20 ppm) (Yates et al. 2004, 2005). These levels were

observed in 6 different bat species from 6 different sampling regions indicating that free-

ranging bats throughout the New England and Mid-Atlantic States are at high risk of Hg

exposure.


7.0 POLICY AND MANAGEMENT RECOMMENDATIONS

This investigation provides critical information to policy makers regarding the

pervasiveness of environmental mercury pollution in the northeastern United States. The

results from this study indicate that mercury levels in songbirds, bats, and invertebrates

throughout the Northeast are high enough to cause detrimental effects to populations

inhabiting areas prone to bioaccumulation of mercury in the terrestrial food web. Reducing

anthropogenic sources of mercury is one essential strategy for minimizing the impact of

mercury on people and wildlife, but to effectively inform policy decisions at each stage of

the process, scientists also need more data. We recommend a concurrent three-pronged

approach for minimizing adverse impacts of mercury on wildlife:

1. Identify the species, habitats, and regions at risk to mercury exposure

2. Address synergistic interactions of mercury with other environmental pollutants

3. Minimize wildlife exposure by reducing mercury emissions.

1. Identify the species, habitats, and regions at risk to mercury exposure.

The first step in identifying mercury risk is to improve mercury monitoring in both aquatic

and terrestrial ecosystems across the United States, by establishing a national mercury

monitoring network. Legislation for a National Mercury Monitoring Network (MercNet)

was introduced into the 112th Congress (to the Senate Public Works and the House Energy

and Commerce Committees) and will provide a comprehensive and standard way for

measuring mercury in the air, water, soil, as well as in fish and wildlife (Schmeltz et al.

2011). Songbirds and bats are nominated as part of the mercury monitoring effort (Mason

et al. 2008). Congress needs to pass legislation authorizing the creation of MercNet, which

will allow the federal government to scientifically evaluate the efficacy of policy and

management decisions that, in turn, will allow for better decisions in the future and protect

past mercury abatement investments

2. Address synergistic interactions of mercury with other environmental pollutants

There is preliminary evidence that mercury can act synergistically with other

environmental stressors, such as acid deposition, making it important to develop science-

based policy recommendations for setting air pollution thresholds to protect and restore

U.S. ecosystems and species (Fenn et al. 2011). A “critical loads” approach to understanding

air pollution impacts requires the assessment of multiple contaminant “loading” to

sensitive ecosystems above which significant adverse impacts are detected. This strategy is

accepted as superior by the scientific and regulatory communities, and is in use in Europe,

Canada, and parts of the United States, but has yet to be used to understand the interaction

of mercury with other contaminants. Although critical loads allow for more refined policy

decisions, their establishment requires firm commitment and funding in order to enable


the most up-to-date scientific determinations. Congress should direct the U.S. EPA to

implement critical loads for sulfur and nitrogen, along with thresholds for mercury, and the

U.S. EPA should use these thresholds to assess progress under the Clean Air Act.

3. Minimize wildlife exposure by reducing mercury emissions.

Mercury emission reduction must occur to effectively minimize wildlife exposure to

mercury, but there are multiple routes that can help us achieve this goal.

First, the U.S. can substantially reduce mercury emissions by implementing best available

pollution control technology for coal-fired power plants. Technological pollution control for

reducing mercury pollution has been enormously successful in the regulation of municipal

and medical waste incinerators (Cain et al. 2011) and the U.S. EPA Mercury and Air Toxics

Standards Rule will provide similar reductions for power plants with a goal of 90% less

mercury emissions (U.S. EPA 2011). It is critical that we ensure implementation of this

common sense solution to the largest stationary source of airborne mercury—coal-fired

power plants.

Second, by avoiding mercury “cap and trade” systems, we will prevent biological mercury

hotspots. While “cap and trade” programs are effective in certain pollution strategies, like

those for acid rain components, it is inappropriate for a pollutant like mercury. There is a

growing body of evidence that local mercury emission sources, such as from coal-fired

power plants, can have significant local effects on downwind ecosystems leading to the

development of biological mercury hotspots (Evers et al. 2007, Driscoll et al. 2007). By

avoiding mercury “cap and trade” systems, our expectation is to prevent new mercury

hotspots from being created across the United States and globally.

Third, the U.S. can take part in regulating global mercury emissions by supporting the

UNEP Mercury Treaty. The United Nations Environment Programme (UNEP) intends to

ratify a globally binding agreement on mercury in 2013 (UNEP Chemicals Branch 2011).

Reductions in the purposeful use of mercury for small-scale gold mining, chlor-alkali

plants, and in manufactured products are planned, while emissions from fossil-fuel burning

and other sources are being negotiated. The U.S. State Department and the U.S. EPA should

continue their international leadership roles in guiding new standards for global mercury

pollution as well as in helping set comprehensive and standard monitoring programs.

Adding new delegates from other federal agencies, such as the Department of Interior, will

help facilitate greater connections with environmental mercury studies and management

in the United States.


8.0 ACKNOWLEDGEMENTS

We are grateful for a grant from The Nature Conservancy’s Rodney Johnson and Katherine

Ordway Stewardship Endowment that supported the development of this publication as

well as parts of the original research. Data collection was made possible by funding from

The Nature Conservancy, New York State Energy Research and Development Authority,

New York State Department of Environmental Conservation, the Wildlife Conservation

Society and the U.S. Fish and Wildlife Service.

This research was the result of years of collaborations and we would like to acknowledge

those that offered their assistance. Many researchers generously shared their data with us.

We are deeply indebted to Dr. David Braun of Sound-Science. We thank Chris Rimmer and

Kent McFarland of the Vermont Center for Ecostudies for their assistance with sampling

Bicknell’s thrushes; Greg Shriver for providing samples from wood thrushes in Delaware;

Sam Edmonds, Nelson O’Driscoll, and the numerous researchers involved with the

International Rusty Blackbird Working Group for sharing their extensive sampling of rusty

blackbirds; Jeff Loukmas from the New York State Department of Environmental

Conservation for providing invertebrate mercury data; Gary Lovett from the Institute for

Ecosystem Studies for supplying soil data; and Chad Seewagen from the Wildlife

Conservation Society for providing multiple years of samples.

Others provided field accommodations, logistical support, and helpful expertise. We thank

the SUNY College of Environmental Science and Forestry’s Adirondack Ecological Center

for providing access to study sites and lodging for field crews; the staff at the Montezuma

National Wildlife Refuge and the Tonawanda Wildlife Management Area for site access and

permits to sample birds and bats; the staff of the Marine Nature Study Area in Hempstead,

NY for logistical support and assistance in the field; Al Hicks of the New York State

Department of Environmental Conservation and John Chenger of Bat Conservation and

Management for their assistance with providing bat samples; Cara Lee at The Nature

Conservancy for helping us with field housing, logistics, and site access; Bruce Connery at

Acadia National Park for helping us with field housing, permits, and site access; Dr. Ford

and staff for assisting us with site selection and permission in the Fernow Experimental

Forest; Bill DeLuca for assisting with sampling efforts, field housing, permits, and site

access in New Hampshire; the Boy Scouts of America for providing access and a field camp

at Massawepie for multiple years; the YMCA for providing housing/field camps and site

access for multiple years; Bill Schuster at Black Rock Forest for providing site access and

permission for multiple years; Bob Mulvihill at Powdermill Avian Research Center for

providing permission, site selection, site access, sampling assistance, samples, and an

incredible learning environment for multiple years; Mike Fowles and site managers at the

U.S. Army Corp of Engineers for providing site permits/access and enthusiastically


assisting with Pennsylvania field logistics; Tom LeBlanc of Allegany State Park for

providing site selection recommendations, logistical support, field housing, and overall

enthusiasm for our project; the staff at numerous National Wildlife Refuges including

Rachel Carson NWR (ME), Wertheim NWR (NY), Parker River NWR (MA), Ninigret NWR

(RI), McKinney NWR (CT); Maine Department of Inland Fisheries and Wildlife; Jen Walsh at

the University of New Hampshire for field assistance; and Henry Caldwell of Dome Island

for providing all kinds of help with boats, field housing, and permits, as well as being a

gracious host for multiple years.

We are especially grateful to the staff of Cornell’s Lab of Ornithology, Conservation Science

department, for their support of this project. In particular, we thank James D. Lowe for all

his devoted work in the field, banding birds and collecting soil, leaves, and bird samples,

and for his assistance with preparing the metadata; Maria Stager for her aid in bird

sampling and banding; Kenneth V. Rosenberg for his departmental support; and Kevin

Webb, from Cornell’s Lab of Ornithology, Information Science department, for his excellent

GIS support.

Within The Nature Conservancy, we appreciate those who supported this work over the

years including: David Higby, Peter Kareiva, Mark King, Cara Lee, Nicole Maher, Rebecca

Shirer, Brad Stratton, Troy Weldy, and Alan White.


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10.0 Appendix A. Common and Latin Names of Songbirds Sampled for Blood Hg Concentrations. Common Name Latin Name

Acadian Flycatcher Empidonax virescens

American Goldfinch Spinus tristus

American Redstart Setophaga ruticilla

American Robin Turdis migratorius

Barn Swallow Hirundo rustica

Bicknell's Thrush Catharus bicknelli

Black-and-White Warbler Mniotilta varia

Black-capped Chickadee Poecile atricapilla

Black-thoated Blue Warbler Dendroica caerulescens

Black-throated Green Warbler Dendroica virens

Blue-headed Vireo Vireo solitarius

Bobolink Dolichonyx oryzivorus

Brown Creeper Certhia americana

Brown Thrasher Toxostoma rufum

Carolina Chickadee Poecile carolinensis

Carolina Wren Thryothorus ludovicianus

Cedar Waxwing Bombycilla cedrorum

Cerulean Warbler Dendroica cerulea

Chipping Sparrow Spizella passerina

Cliff Swallow Petrochelidon pyrrhonota

Common Grackle Quiscalus quiscula

Common Yellowthroat Geothlypis trichas

Dark-eyed Junco Junco hyemalis

Eastern Kingbird Tyrannus tyrannus

Eastern Phoebe Sayornis phoebe

Eastern Towhee Pipilo erythrophthalmus

Eastern Wood-Pewee Contopus virens

Grasshopper Sparrow Ammodramus savannarum

Gray Catbird Dumetella carolinensis

Great Crested Flycatcher Myiarchus crinitus

Hermit Thrush Catharus guttatus

Hooded Warbler Wilsonia citrina

House Wren Troglodytes aedon


Indigo Bunting Passerina cyanea

Least Flycatcher Empidonax minimus

Lincoln's Sparrow Melospiza lincolnii

Louisiana Waterthrush Parkesia moacilla

Magnolia Warbler Dendroica magnolia

Marsh Wren Cistothorus palustris

Mourning Warbler Oporornis philadelphia

Myrtle Warbler (Yellow-rumped) Dendroica coronata

Nelson's Sparrow Ammodramus nelsoni

Northern Cardinal Cardinalis cardinalis

Northern Parula Parula americana

Northern Rough-winged Swallow Stelgidopteryx serripennis

Northern Waterthrush Parkesia noveboracensis

Ovenbird Seiurus aurocapillus

Prairie Warbler Dendroica discolor

Red-breasted Nuthatch Sitta canadensis

Red-eyed Vireo Vireo olivaceus

Red-winged Blackbird Agelaius phoeniceus

Rose-breasted Grosbeak Pheucticus ludovicanus

Rusty Blackbird Euphagus carolinus

Saltmarsh Sparrow Ammodramus caudacutus

Savannah Sparrow Passerculus sandwichensis

Scarlet Tanager Piranga olivacea

Seaside Sparrow Ammodramus maritimus

Song Sparrow Melospiza melodia

Swainson's Thrush Catharus ustulatus

Swamp Sparrow Melospiza georgiana

Traill's Flycatcher (Willow/Alder) Empidonax traillii/E. alnorum

Tree Swallow Tachycineta bicolor

Tufted Titmouse Baeolophus bicolor

Veery Catharus fuscescens

White-breasted Nuthatch Sitta carolinensis

White-eyed Vireo Vireo griseus

White-throated Sparrow Zonotrichia albicollis

Winter Wren Troglodytes troglodytes

Wood Thrush Hylocichla mustelina

Worm-eating Warbler Helmitheros vermivorus

Yellow Palm Warbler Setophaga palmarum

Yellow-bellied Flycatcher Empidonax flaviventris

Yellow-throated Vireo Vireo flavifrons


Yellow-throated Warbler Setophaga dominica


11.0 Appendix B – SONGBIRD MERCURY EXPOSURE BY SPECIES

Species N Mean Blood Hg Level (ppm) ±

SD Range States Sampled

Bombycillidae

Cedar Waxwing 5 0.0468 ± 0.0231 0.0122 – 0.0691 VA

Cardinalidae

Indigo Bunting 11 0.2538 ± 0.4810 0.0169 – 1.6700 NY, VA

Northern Cardinal 2 0.1824 ± 0.1564 0.0718 – 0.2930 VA

Rose-breasted Grosbeak 1 0.0241 — NY

Scarlet Tanager 10 0.0645 ± 0.0387 0.0179 - 0.1180 NY, PA, VA

Certhiidae

Brown Creeper 1 0.0897 — NY

Emberizidae

Chipping Sparrow 3 0.2200 ± 0.1330 0.1260 - 0.3140 ME, PA

Eastern Towhee 1 0.0761 — NY

Grasshopper Sparrow 1 0.0502 — VA

Lincoln's Sparrow 23 0.1574 ± 0.1697 0.0128 - 0.6640 ME, NY

Nelson's Sparrow 97 0.5412 ± 0.3440 0.1070 - 2.0000 MA, ME

Saltmarsh Sparrow 479 0.7531 ± 0.4779 0.0292 - 3.7300 CT, MA, ME, NY, RI

Savannah Sparrow 2 0.0221 ± 0.0023 0.0205 – 0.0237 NY

Slate-colored Junco 4 0.0484 ± 0.0378 0.0200 – 0.1030 ME, NY, VA

Song Sparrow 109 0.1423 ± 0.1162 0.0157 - 0.5226 MA, ME, NY, PA, RI, VA

Swamp Sparrow 4 0.2043 ± 0.0348 0.1568 – 0.2384 MA, NY

Seaside Sparrow 8 0.4924 ± 0.2333 0.1470 - 0.7749 CT, NY

White-throated Sparrow 3 0.0124 ± 0.0006 0.0131 – 0.0120 ME

Fringillidae

American Goldfinch 3 0.0039 ± 0.0029 0.0058 - 0.0005 ME, VA

Hirundinidae

Barn Swallow 5 0.1304 ± 0.0281 0.1053 - 0.1660 ME

Cliff Swallow 25 0.2067 ± 0.0925 0.0840 - 0.4710 ME

Northern Rough-winged Swallow 2 0.0414 ± 0.0068 0.0366 - 0.0462 VA




Tree Swallow 5 0.1997 ± 0.0176 0.1830 - 0.2180 ME

Icteridae

Bobolink 2 0.0327 ± 0.0253 0.0148 - 0.0506 CT, ME

Common Grackle 3 0.1294 ± 0.0339 0.0963 - 0.1640 VA

Red-winged Blackbird 40 0.2380 ± 0.2355 0.0115 - 9.418 MA, ME, NY, VA

Rusty Blackbird 93 0.6555 ± 0.4111 0.0931 - 1.066 ME, NH, VT

Mimidae

Brown Thrasher 1 0.0567 — PA

Gray Catbird 2 0.0589 ± 0.0018 0.0576 - 0.0602 PA

Paridae

Black-capped Chickadee 11 0.1007 ± 0.0739 0.0113 - 0.2300 NY, PA

Boreal Chickadee 1 0.0683 — ME

Carolina Chickadee 1 0.0308 — VA

Tufted Titmouse 3 0.0944 ± 0.0761 0.0448 - 0.1820 NY, VA

Parulidae

American Redstart 15 0.0633 ± 0.0405 0.0173 - 0.1860 NY, PA

Black and White Warbler 3 0.0623 ± 0.0131 0.0474 - 0.0717 NY, PA

Blackpoll Warbler 21 0.0575 ± 0.0140 0.0343 - 0.0817 ME, NH, NY

Black-throated Blue Warbler 8 0.0472 ± 0.0210 0.0175 - 0.0704 NY, VA

Black-throated Green Warbler 5 0.0541 ± 0.0308 0.0243 - 0.1060 NH, NY, VA

Blue-winged Warbler 1 0.0719 — VA

Cerulean Warbler 3 0.0163 ± 0.0047 0.0118 - 0.0211 PA

Common Yellowthroat 15 0.1585 ± 0.1139 0.0365 - 0.4057 CT, MA, ME, NY, PA

Hooded Warbler 7 0.0815 ± 0.0567 0.0306 - 0.1780 NY, PA, VA

Louisiana Waterthrush 20 0.2073 ± 0.1489 0.0527 - 0.6202 NY, PA, VA

Magnolia Warbler 10 0.1209 ± 0.0834 0.0419 - 0.2900 ME, NH, NY, PA

Mourning Warbler 1 0.0169 — NY

Myrtle Warbler 8 0.1217 ± 0.0845 0.0671 - 0.3180 ME, NY

Northern Parula 1 0.0351 — VA




Northern Waterthrush 6 0.2346 ± 0.1706 0.0746 - 0.5660 ME, NY

Ovenbird 37 0.0514 ± 0.0500 0.0102 - 0.2950 ME, NY, PA, VA

Prairie Warbler 1 0.0420 — NY

Worm-eating Warbler 5 0.0712 ± 0.0612 0.0236 - 0.1610 NY, VA

Yellow Palm Warbler 9 0.5643 ± 0.4082 0.1940 - 1.4900 NY

Yellow-throated Warbler 2 0.2640 ± 0.2022 0.121 – 0.407 VA

Sittidae

Red-breasted Nuthatch 1 0.1440 — NY

White-breasted Nuthatch 4 0.1131 ± 0.0814 0.0664 – 0.2350 NY, PA, VA

Troglodytidae

Carolina Wren 28 0.1865 ± 0.1206 0.0172 - 0.5160 VA

House Wren 1 0.123 — PA

Marsh Wren 2 0.2450 ± 0.0028 0.2430 - 0.2470 CT

Winter Wren 1 0.0646 — NH

Turdidae

American Robin 16 0.0716 ± 0.0589 0.0039 - 0.1910 ME, NY, PA, VA, VT, WV

Bicknell's Thrush 50 0.1231 ± 0.1224 0.0130 - 0.7946 ME, NH, NY, VT

Hermit Thrush 113 0.0683 ± 0.0552 0.0143 - 0.5130 ME, NH, NY, PA, VT

Swainson's Thrush 56 0.0832 ± 0.0383 0.0296 - 0.2380 ME, NH, NY, VT

Veery 104 0.0517 ± 0.0323 0.0034 - 0.1648 MA, NH, NY, PA, VA, VT, WV

Wood Thrush 160 0.0881 ± 0.0759 0.0016 - 0.6923 DE, ME, NY, PA, VA, WV

Tyrannidae

Acadian flycatcher 12 0.2934 ± 0.1314 0.1320 - 0.5230 VA

Eastern Kingbird 1 0.0807 — NY

Eastern Phoebe 3 0.1653 ± 0.0726 0.0886 - 0.2330 NY, VA

Eastern Wood-Pewee 2 0.8688 ± 0.4293 0.5653 - 1.1723 NY

Great Crested Flycatcher 2 0.1629 ± 0.0398 0.1347 - 0.1910 NY, VA

Least Flycatcher 1 0.15812 — NY

Traill's Flycatcher 6 0.2966 ± 0.2254 0.1160 - 0.7130 MA, NY




Yellow-bellied Flycatcher 3 0.1208 ± 0.0613 0.0780 - 0.1910 NH, NY

Vireonidae

Blue-headed Vireo 6 0.0859 ± 0.0736 0.0149 - 0.2050 NY, PA, VT

Red-eyed Vireo 153 0.0957 ± 0.0819 0.0080 - 0.5140 MA, ME, NY, PA, VA, VT, WV

White-eyed Vireo 2 0.0360 ± 0.0141 0.0260 - 0.0460 PA

Yellow-throated Vireo 2 0.3944 ± 0.4544 0.0731 - 0.7157 NY, VA


12.0 Appendix C – SONGBIRD MERCURY EXPOSURE BY FAMILY

Figure 45. Mean plus standard deviation of blood Hg concentrations in Cardinalidae

species.

Figure 46. Mean and maximum level detected of blood Hg concentrations in Emberizidae

species.

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Blo

od

Hg

(pp

m),

ww

Cardinalidae

Maximum Species Value Detected

Mean + SD

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Blo

od

Hg

(pp

m),

ww

Emberizidae


Mean + SD


Figure 47. Mean and maximum blood Hg concentrations in Hirundinidae species.


concentrations in Icteridae species.

0.0

0.2

0.4

0.6

0.8

1.0

Blo

od

Hg

(pp

m),

ww

Hirundinidae


Mean + SD

0.0

0.4

0.8

1.2

1.6

2.0

2.4

Blo

od

Hg

(pp

m),

ww

Icteridae


Mean + SD



concentrations in Paridae species.


concentrations in Parulidae species.

0.0

0.2

0.4

0.6

0.8

1.0

Carolina Chickadee

(N = 1)

Boreal Chickadee (N = 1)

Eastern Tufted Titmouse

(N = 3)

Black-capped Chickadee

(N = 13)

Blo

od

Hg

(pp

m),

ww

Paridae


Mean + SD

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Blo

od

Hg

(pp

m),

ww

Parulidae


Mean + SD



concentrations in Sittidae species.


concentrations in Troglodytidae species.

0

0.2

0.4

0.6

0.8

1

Red-breasted Nuthatch (N = 1) White-breasted Nuthatch (N = 4)

Blo

od

Hg

Leve

l (p

pm

), w

w

Sittidae


Mean + SD

0.0

0.2

0.4

0.6

0.8

1.0

Blo

od

Hg

(pp

m),

ww

Troglodytidae


Mean + SD



concentrations in Vireonidae species.

0.0

0.2

0.4

0.6

0.8

1.0

Blo

od

Hg

(pp

m),

ww

Vireonidae


Mean + SD

mercury contamination within terrestrial ecosystems in new ... · lane, and j. franklin. 2011....

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