research and resource management at audubon canyon ranch

◗ behavior in

heronries

Common Raven

◗ spatial dimensions

Raven home

ranges

◗ power of rainfall

Livermore

Marsh

◗ a test case

Eliminating

Ehrharta

◗ unseen soil

dwellers

Ehrharta

underground

2004

the ArdeidResearch and

Resource Management

at Audubon Canyon Ranch

2004 the ARDEID page 1

It’s as if the ravens are not even there.Although Common Ravens fly frequent-ly through some heronries in search of

opportunities to prey on eggs and chicks,nesting Great Egrets exhibit little or nodefiance. In fact, they seem to show a com-plete lack of interest or concern. In addi-tion, Great Egrets leave their nestsunguarded as nestlings approach threeweeks of age, several weeks before youngegrets can fly—even though many of thesebroods are taken by patrolling ravens.

New cohorts of herons and egrets con-tinue to disperse from heronries eachsummer and to contribute beautifully tothe life in our marshes and estuaries. Butraven numbers are booming throughoutmost of the San Francisco Bay area (seeThe Ardeid 2001). Whether heron andegret populations will continue to repro-duce adequately under the growing pres-ence of ravens or, alternatively, suffermajor declines in productivity hasbecome a common concern amongobservers of heronries. The particularthreat posed by ravens is difficult tounderstand fully, because most instancesof nest predation are phantom eventsrevealed only by sudden nest vacancies.

The wisdom of egret behaviors in thepresence of ravens is also mysterious.Their apparent carelessness is consistentamong individuals and structured by along evolution of adaptive responses tocomplex ecological forces, including nestpredation. Scientific attempts to under-stand how birds respond to the risk ofnest predation have failed to discover reli-able ways to predict nest success. There-fore, to learn more about the threat ofgrowing raven populations on heron andegret nesting colonies (see The Ardeid2002), I conducted an investigation ofpredator—rather than prey—behaviors(Kelly et al. in review). Collaboratorsincluded ACR’s Katie Etienne, JenniferRoth of PRBO, several ACR field biologists,and numerous volunteer observers.Specifically, we asked: under what condi-tions and to what extent do ravens exploitheronries for food?

Measuring every move

From 1999 through 2003, AudubonCanyon Ranch field observers meas-ured nest mortality and raven

occurrence at all of the known heronriesin the northern San Francisco Bay area(Figure 1). At ten of these sites, we con-ducted two all-day watches for ravenactivity. We then selected three heronrieswith resident ravens for more intensivestudy: (1) ACR’s Picher Canyon, near theshoreline of Bolinas Lagoon, where GreatBlue Herons, Great Egrets, and SnowyEgrets settle among the branches of coastredwoods in the bottom of a narrowcanyon; (2) Drakes Estero in the PointReyes National Seashore, where nestingGreat Egrets and Great Blue Heronscrowd into a small patch of bishop pines

surrounded by grazed prairie grasses andvegetated dunes; and (3) West MarinIsland, a 2.7-acre “rock” in the MarinIslands National Wildlife Refuge just offthe eastern Marin County shoreline,where a blend of California buckeyes andwoody shrubs often supports the SanFrancisco Bay area’s largest concentrationof nesting Great Egrets, Snowy Egrets,Black-crowned Night-Herons, and GreatBlue Herons (see The Ardeid 2003).

At each of the three heronries selectedfor close study, we recorded detailedinformation on raven occupancy, land-ings, patrol flights, and interactions withother species. At five-minute intervalsduring hundreds of two-hour observationperiods, we recorded the presence of

Common Raven behaviors in heronries

Vague Consequences of Omnipresenceby John P. Kelly

continued on page 2

Figure 1. Study area and heronries (circles) in the northern San Francisco Bay area, including colony sitesfor extended watches (*) and intensive observations of raven activity (PICA: Picher Canyon; WMAR: WestMarin Island; DRES: Drakes Estero).

Audubon Canyon RanchResearch and ResourceManagement

Executive StaffSkip Schwartz, Executive DirectorJohn Petersen, Associate DirectorYvonne Pierce, Administrative DirectorStaff BiologistsJohn Kelly, PhD, Director, Research & Resource

ManagementRebecca Anderson-Jones, Bouverie PreserveKatie Etienne, Research CoordinatorDaniel Gluesenkamp, PhD, Habitat Protection and

Restoration SpecialistGwen Heistand, Bolinas Lagoon PreserveLand StewardsBill Arthur, Bolinas Lagoon PreserveDavid Greene, Tomales Bay propertiesJohn Martin, Bouverie PreserveField BiologistsEllen BlusteinLauren HammackMark McCaustlandMichael ParkesData ManagementMelissa DavisResearch AssociatesJules EvensFlora MacliseHelen PrattRich StallcupResource Management AssociatesLen BluminRoberta DowneyScientific Advisory PanelSarah Allen, PhDPeter Connors, PhDJules EvensKent Julin, PhDGreg KammanRachel KammanChris Kjeldsen, PhDDoug Oman, PhDHelen PrattW. David ShufordRich StallcupWesley W. Weathers, PhD

the ARDEID 2004

Nancy Abreu (H); Ken Ackerman(C,G,S,W); Drew Alden (R); Judy Allen(C); Leslie Allen (R); Sarah Allen (S); BobAnderson (H); Janica Anderson (H);Autodesk employees (R); Bob Baez(S,W); Norah Bain (H); Bruce Bajema(H,S); Katy Baty (W); Tom Baty (W);Gordon Bennett (S,W); Shelly Benson(R,W); Sherman Bielfelt (G); Gay Bishop(S); Mike Blick (G); Julie Blumenthal(W); Len Blumin (R,W); Patti Blumin(H,R); Ellen Blustein (H,S); Noelle Bon(H); Janet Bosshard (H); Tom Bradner(E); Anna-Marie Bratton (E); EmilyBrockman (H,S,W); Ken Burton (S,W);Phil Burton (H); Denise Cadman (H);Ann Cassidy (H); Bonnie Clark (S);Michelle Coppoletta (R); Rig Currie (S);Melissa Davis (H); Nick Degenhardt (H);Jack Dineen (H); Carolyn Dixon (H);Giselle Downard (H); Roberta Downey(C,R); Joe Drennan (W); Judy Dugan (E);Bob Dyer (H); Cathy Evangelista (H);Jules Evens (R,S,W); Katie Fehring(S,W); David Ferrera (W); John Finger(R); Binny Fischer (H); Grant & GinnyFletcher (P,S); Carol Fraker (H); DanielGeorge (S,W); Tony Gilbert (H,S,W);Beryl & Dohn Glitz (H); Mike Green(W); Philip Greene (H); Bill Grummer(H); Karlene Hall (R); Madelon Halpern(H); Lauren Hammack (M); FredHanson (S,W); Roger Harshaw (S);Michael Henkes (G); Diane Hichwa(H,S); Judy Hiltner (C); Peter Horn (S);Roger Hothem (H); Steve Howell (W);Lisa Hug (S,W); Jeri Jacobson (H,S);Rosemary Jepson (G); Rick Johnson(H,S,W); Calvin Jones (G); Gail Kabat(W); Lynnette Kahn (H,S); BobKaufman (H); Guy Kay (H); ThomasKehrlein (G); Richard Kirschman (S);

Ellen Krebs (H); Carol Kuelper (S); AndyLaCasse (H); Joan Lamphier (H); Jean-Michel Lapeyrade (G); Laura Leek (W);Bill Lenarz (H); Stephanie Lennox (H);Robin Leong (H); Liz Lewis (M); EileenLibby (H); Patricia Lonacker (R); FloraMaclise (H); Phil Madden (R); Art &Lynn Magill (R); Jean Mann (R); AlanMargolis (R); Marin Conservation Corps(R); Roger Marlowe (W); Janaea Martin(G); Mark Mc Caustland (H,M,S); DavidMcConnell (H); Jean Miller (H); AnnMintie (E); Len Nelson (H); WallyNeville (H); Linda Nicoletto (C); TerryNordbye (S,W); Richard Panzer (H);Jennie Pardi (H); Bob Parker (G); MikeParkes (H,R,S,W); Lorraine Parsons (M);Tony Paz (E); Joelle Peebles (G);Precious Peoples (H); Kate Peterlein(S,W); Jeff and Kathy Peterson (R);Myrlee Potosnak (H); Linda & JeffReichel (H); Rudi Richardson (W);DeAnn Rushall (T); Ellen Sabine (H);Marilyn Sanders (H); Fran Scarlett (H);Cindy Schafer (S); Phyllis Schmitt (H,R);Gordon & Laurie Schremp (H); AliceShultz (H); Asha Setty (C); Joe Smith(W); Anne Spencer (S); Bob Spofford(H); Rich Stallcup (M,S); JeanStarkweather (H); Jim & JeanneSternbergh (H); Michael Stevenson(S,W); Ron Storey (H); John Sutherland(C); Lowell Sykes (H,S,W); Judy Temko(H,S); Janet Thiessen (H); Gil & DodieThomson (H); Peggy Thorpe (H); LisaToet (E,R); Travelsmith employeeservice day (R); Sue Tredick (H); SusanTremblay (G); Tanis Walters (S); RyanWatanabe (R); Penny Watson (W);Rosilyn & Tom White (W); PhyllisWilliams (H); Jessica Wilson (C); KenWilson (W); Katy Zaremba (R).

In this issue

Vague Consequences of Omnipresence: Common Raven behavior in heronries ◗by John P. Kelly ......................................................................................................................page 1

The Spatial Dimensions of Raven Life: Home-range dynamics in western Marin County◗by Jennifer Roth ....................................................................................................................page 4

Eliminating Ehrharta: Bolinas Lagoon Preserve as a test area for regional conservation ◗by Daniel Gluesenkamp ........................................................................................................page 6

Ehrharta Underground:

◗by Gwen Heistand..................................................................................................................page 6

The Power of Rainfall: Influences on the hydro-geomorphology of Livermore Marsh◗by Katie Etienne ....................................................................................................................page 10

Cover photo: Common Raven by Peter LaTourrette ◗ Ardeid mastheadGreat Blue Heron ink wash painting by Claudia Chapline

Volunteers for ACR research or habitat restoration projects since TheArdeid 2003. Please call (415) 663-8203 if your name should have beenincluded in this list.

PROJECT CLASSIFICATIONS:

C = Coastal Habitat Restoration at Toms Point ◆ E = Ehrharta erecta Removal atBolinas Lagoon Preserve ◆ G = Grassland Management at Bouverie Preserve ◆H = Heron/Egret Project ◆ M = Livermore Marsh and Olema Marsh Surveys ◆◆ P = Photo Points ◆ R = Habitat Restoration ◆ S = Tomales Bay ShorebirdProject ◆ T = Turkey Research at Bouverie Preserve ◆ W = Tomales BayWaterbird Census

The Watch

the ARDEID 2004

ravens in and near colony sites, identifiedperching substrates, and noted their posi-tions above or below the tree canopy oron open ground. We measured how longravens remained at each landing site andestimated their distances to heron oregret nests. Whenever a raven landed inor near a nest, we recorded the nest con-tents, nesting stage, age of chicks, andnumber of adult herons or egrets flushedfrom the area. For each patrol flight, werecorded the time of day, flight duration,height above nests, and alert responses ofadult or nestling herons or egrets. Whenravens interacted with other bird species,we determined which individuals weredominant and subordinate, the durationof chases, and other details. And ofcourse, we recorded any evidence of nestpredation. From these data, we looked forevidence that the nest predatory behav-iors of ravens might be influenced bytheir foraging experience, energy needs,time of day or season, or the availabilityof prey.

Evaluating occurrence

Our surveys revealed substantialnest predation by ravens at someheronries in the region but high

variability among colony sites—eventhough ravens are common throughoutthe San Francisco Bay area. We estimateda regional average of only about oneraven occurrence in each heronry everyfive hours and detected ravens in onlyabout one-fourth of the heronries eachyear. At Picher Canyon, resident ravenswere present less than 5% of the time, butravens occupied colonies at West MarinIsland and Drakes Estero about 30% ofthe time. The resident ravens occupied allthree sites of intensive study more oftenafter mid-June, often in pairs or accom-panied by fledgling ravens. Keep in mind,however, that ravens occurred only rarelyat most other heronries.

Resident ravens preyed on about 27Great Egret nests per year at West MarinIsland, 20 nests per year at PicherCanyon, and only two to three nests peryear at Drakes Estero. Great Blue Heronnest mortality was less than two nests peryear at each site and, for most of these,we did not determine the cause of failure.Of 11 instances of complete colony siteabandonment in the region, only one—ata site with nesting Great Blue Herons andGreat Egrets—was associated with repeat-ed heavy disturbance by ravens, and asingle Great Blue Heron nest was estab-lished there the following year.

The low regional rates of raven occur-rence and nest predation in heron andegret colonies were associated with recentinfluxes of ravens. If ravens move into anarea without prior experience in heron-ries, they may exhibit “neophobia” for thefirst few to several nesting seasons. Neo-phobia is a characteristic cautiousnesstoward novel food items that subsides asravens learn through experience not tofear what may later become important

food. Because nesting ravens occupy thesame home ranges across years (see arti-cle on page 3), nest predation in waterbirdcolonies by new resident pairs of ravensmight increase as neophobia subsides.

We did not find significant annualincreases in nest predation, but we didfind significant annual increases in ravenpredatory behaviors: longer patrol flights,more landings, more frequent movementamong landing sites, and more flushingand harassment of nesting Great Egrets. Inaddition, recovered (fresh) prey remains atthe Marin Islands suggested increasingpredation of adult Snowy Egrets: ravenskilled at least four adult Snowies in 2000,seven in 2001, 15 in 2002, and eight in2003. On one occasion, ACR biologistMark McCaustland watched in awe as araven chased an adult Snowy Egret to theground and killed it. Such trends in behav-ior are consistent with the attenuation ofneophobia in adult ravens and suggestthat nest predation might increase annu-ally for some years after ravens begin tooccupy heronries.

The notion that ravens might becomemore daring predators across years isconsistent with previously known behav-iors. For example, ravens may have diffi-culty overcoming neophobia by their typ-ical means of approaching slowly(Heinrich 1988, Condor 90: 950-952),because egrets build their nests in isolat-ed locations in the nest-tree canopy.Ravens also require unusually long peri-ods of time, under experimental condi-tions, to accept carcasses of large birds(Heinrich et al. 1995, Auk 112: 499-503).Perhaps most importantly, however, therisk of major injury if egrets becomedefensive may be enough to prolong theirneophobic behavior.

Assessing predation risk

The lack of annual increases in nestpredation at the three study sites, inspite of annual increases in associ-

ated behaviors, suggests that residentravens may interfere with the activities ofother nest predators, such as raccoons,owls, or raptors. Ravens were dominant in93% of interactions with visiting birdspecies such as Osprey, Golden Eagle,Red-tailed Hawk, Peregrine Falcon, andAmerican Crow. In one instance, a Red-tailed Hawk that was flushing egrets fromtheir nests at the Marin Islands washarassed repeatedly by the residentravens until it left the area. Althoughravens often chase visitors away, they alsorespond opportunistically to nest distur-

Figure 2. Raven predation on Great Egret nests,length of raven patrol flights, and number of raveninteractions with other species increased signifi-cantly (P < 0.05) with increased raven productivity.

Figure 3. Great Egret nest failures known to haveresulted from raven predation peaked as nestlingsapproached three weeks of age, at ACR’s PicherCanyon, 2000-2001.

see Omnipresence, page 5


Early one morning, a pair of ravensflies over the heron and egretcolony at ACR’s Picher Canyon in

search of unattended eggs or youngchicks. At Point Reyes National Seashore,ravens soar routinely over dune beachesin search of Snowy Plover nests. Mean-while, at Tony’s Seafood Restaurant onTomales Bay, a pair of ravens lingers eachday in the vicinity of a nearby dumpster.What impact is raven predation having onheronries and rare bird species? What fac-tors are influencing their movements anduse of the landscape? These questionsprompted us to begin radio-trackingbreeding ravens in western Marin Countyin order to learn more about their impacton sensitive bird species and the factorsaffecting their distribution (Roth et al.2004).

Radio-tracking

We captured and attached back-pack-mounted radio-transmit-ters to 16 adult ravens from 15

resident pairs, including both members ofthe pair residing near Picher Canyon.

Capturing ravens was one of the most dif-ficult parts of the study, and we went togreat lengths to outsmart these intelligentbirds. We started by identifying birds thatwe were interested in studying and thenwatched them for several days to learnmore about their habits and decide on asuitable trapping location. Once wedecided to attempt a capture, we roseseveral hours before dawn to place thebait and hide our traps and ourselvesbefore first light; the birds would avoidthe area for days at the first hint thatsomething was amiss. We hid in bushesand ditches, covering ourselves withbranches and dried grass. We often spentseveral hours in our makeshift blindsbefore the ravens came near the bait.Ravens are surprisingly cautious aroundunknown food sources, often approach-ing the area and backing away severaltimes before eating anything. Mean-while, we waited breathlessly as theyapproached the traps or moved into aposition where we could shoot a net overthem. Our disappointment over nearmisses was tangible.

On one occasion, a bird that discov-ered our traps and escaped without beingcaptured flew into the air, circling andcalling angrily. Ravens came from alldirections. We soon had a large group ofravens circling the area and calling. Thewarning had gone out! Conversely, imag-ine our excitement each time we handledone of these large, intelligent birds. Eachbird responded differently to being cap-tured; some birds struggled and othersquietly observed us. Each release was fol-lowed by a few tense moments as wewatched to see whether there would beany problems with the harnesses we usedto attach the radio-transmitters to thebirds. Fortunately, all radio-tagging activi-ties were successfully completed withoutmishap, but the challenges of followingtheir movements were just beginning.

We radio-tracked each bird for one tothree years. Each time we detected a bird,we mapped its location on a topographicmap and recorded information on behav-ior and habitat use. For example, werecorded birds flying over grazed grass-lands, foraging along beaches, attendingnests in cypress trees, and roosting inpine groves. We also mapped nest sitesand concentrated food sources in thearea. We used the data we collected toestimate the home-range size of each birdand to evaluate some of the factors likelyto affect home-range size and space usewithin home ranges.

Home-range size

Ahome range is the area used by ananimal during normal activitiessuch as food gathering, mating,

and caring for young. We measured eachhome range by calculating the area that

Home-range dynamics in western Marin County

The Spatial Dimensions of Raven Lifeby Jennifer E. Roth

Figure 1. Locations, centers of activity (50%occurrence), and home ranges (95% occurrence)of the female (dashed lines) and male (solid lines)ravens nesting near ACR’s Picher Canyon heronry.Unlabeled outlying areas are isolated portions ofhome ranges.

continued on page 4

the ARDEID 2004

encompassed a 95% probability of anindividual raven’s occurrence, assumingthat this area would include all normalactivities and exclude rare excursions tomore distant areas (Figure 1).

Home-range size was highly variablefor the ravens in our study (Figure 2).Sizes ranged from 0.2–4.9 km2 for femalesand 0.3–4.9 km2 for males. The homeranges of the Picher Canyon pair werelarge compared to other pairs: 4.2 km2 forthe female and 4.9 km2 for the male.

Many factors may contribute to varia-tion in home-range size among individu-als. For example, food supply, competi-tion for food, territoriality, vegetationtype, and body size might influence thedistances birds must travel. We tested thepossibility that differences in sex and dis-tance to important sources of food couldexplain the large differences in home-range size among ravens in westernMarin County.

Sex differences

Sex may influence home-range size inbirds when there are differences inbody size or behavior between

females and males. When males andfemales differ greatly in size, associateddifferences in agility and power mightallow them to compete less for particularprey or perhaps increase their collectivemenu of available prey. However, maleravens are only slightly larger thanfemales. Nonetheless, we expected to finda difference between female and malehome-range sizes during the breeding

season due to differences inbehavior between the sexes:females are largely responsi-ble for incubation and malesleave the vicinity of the nestto forage while females areattending the nest. Contraryto our expectations, home-range size did not differ sig-nificantly between femaleand male ravens in our study.Also, we did not find a signifi-cant difference in the distri-bution of locations for thefemale and male of the PicherCanyon pair (Figure 1). It maybe that sex roles do not differenough during the breedingseason to affect overall home-range size in ravens. Alterna-tively, the similar home-rangesizes between male andfemale ravens may reflecttheir tendency to interact fre-quently with their mates

through courtship, pair-bond reinforce-ment, increased vigilance by the maleduring egg laying and incubation, orother social behaviors associated withnesting (Boarman and Heinrich 1999).

Distance to food sources

In general, prey abundance and dis-tance to food and water influencehome-range size and movements in

birds. Besides preying on egret eggs andchicks, ravens in our study fed on smallmammals and reptiles; grain, calf carcass-es, and afterbirths found at many localdairies; human refuse at beaches, parkinglots, and dumpsters; and eggs and youngof other birds in the area. On severaloccasions, we even saw ravens harassTurkey Vultures until they regurgitatedtheir food. The ravens were able to catchthe regurgitations in mid-air! However,despite the wide variety in raven diets andsome unusual foraging behaviors, home-range sizes are most likely to be influ-enced by the locations of stable, concen-trated sources of food.

We determined the distance betweeneach raven nest and the nearest ranch,human food source, or waterbird colonyin order to evaluate the influence of con-centrated food sources on home-rangesize. We found a general trend indicatingthat ravens nesting farther away fromconcentrated food sources had largerhome ranges (Figure 2). For instance, thePicher Canyon ravens nested about 1 kmaway from the heron and egret colony,which was the nearest concentrated food

source to their nest, and they occupiedrelatively large home ranges compared toother ravens in western Marin County(Figure 2).

Space use within home ranges

Birds are likely to use some areasmore intensively than others due tothe patchy distribution of food and

habitat areas suitable for feeding, cachingfood, and nesting. We evaluated space usewithin home ranges to determinewhether ravens’ locations exhibited ran-dom, uniform, or clumped distributions.We also estimated the size of core areas orcenters of activity, defined as areas with a50% probability of an individual raven’soccurrence (Figure 1). We found that loca-tions of females were significantlyclumped within 83% and 100% of homeranges in 2000 and 2001, respectively.Males were more variable in their use ofspace, with locations clumped in only38% and 44% of home ranges in 2000 and2001, respectively.

We used these data to determine therelationship between centers of activity,nest sites, and concentrated food sources.All 16 of the radio-tagged birds centeredtheir activities around their nest sites. Insome cases, there was a concentratedfood source within that center of activity.Other birds had two centers of activity,with one centered around the nest siteand one centered around a concentratedfood source. The Picher Canyon ravenswere unique among the individuals westudied in having three distinct centers ofactivity that centered around (1) theirnest site, (2) the Picher Canyon heron andegret colony, and (3) a nearby horse ranchwhere they could rely on a daily supply ofgrain at feeding time (Figure 1). Theseactivity centers were separated by habitatareas that the ravens only rarely occupied.

Annual variation

Like most things in nature, food sup-ply, habitat quality, and other factorsthat affect home-range use, may

vary from year to year, causing correspon-ding changes in home-range size. Wecompared home-range sizes betweenyears and found no significant differ-ences-large home ranges remained largeand small ones remained small. However,there were significant small-scale shifts inhome-range placement for most females(67%) and males (63%). These shiftswere associated with changes in nestlocation and the distribution of desirablefood resources between years. Given the

Figure 2. Raven home-range size increases with the distancebetween the nest and the nearest concentrated food source (P <0.05). Labels indicate the home ranges of ravens occupying famil-iar locations in western Marin County. The male raven at PicherCanyon was not included in the analysis. Note the log scale onboth axes.

continued page 5, top

bances by other predators or humans.We did not test directly whether ravensinfluence other nest predators, but ourresults suggested that ravens mightreduce or displace the nest predatoryactivities of other species: raven preda-tion on nestling Great Egrets at PicherCanyon did not differ significantlyfrom 1968–1979 predation levels (Prattand Winkler 1985, Auk 102: 49-63),when ravens were not present(P=0.56).

One consistent pattern we foundwas that ravens with large familiesengaged in more nest predatory activi-ty (Figure 2, page 2). This suggests thatthe extent of raven predation dependson the food demand of residentravens. If so, nest predation might bemanaged effectively by limiting ravenreproductive success. However, this inter-esting possibility has not been tested.

At the Marin Islands, we surveyed preyremains in the vicinity of the raven nestand in a cache and shell dump area usedroutinely by the resident ravens. Theresults of these surveys, and the timingand rates of nest predation on GreatEgrets, indicated that the resident ravensobtained most or all of their energy needsfrom the heronry. Such dependence onthe heronry for food is consistent with theapparent link between predatory activityand food demand in resident ravens, butcontrasts strongly with low rates of nestpredation at most other colony sites inthe region. At other sites, alternative foodsources may be more available. For exam-ple, resident ravens at Picher Canyonspend much of their time feeding at ahorse ranch approximately 2 km from


apparent association between ravens andconcentrated food sources in the area,variation in the size and placement ofhome ranges likely reflected variation ingrazing or harvesting rotations on ranch-es, the distribution of and access tohuman foods and garbage, and the sea-sonal timing and reproductive success ofnearby waterbird colonies.

It may be no surprise that the way inwhich ravens are distributed across thelandscape is related to both natural andanthropogenic features of the environ-ment. Raven populations are increasingin many parts of the San Francisco BayArea (Kelly et al. 2002; see The Ardeid2002) and throughout the western United

States (Sauer et al. 1997). Their successfuladaptation to human-dominated land-scapes has likely been a major contribut-ing factor to these population increases,and such adaptations are evident in thehome-range dynamics of individualsravens. Because ravens structure theirlives, in part, around ours, human landuse has become an important considera-tion for resource managers concernedwith the effects of increasing raven popu-lations on sensitive species (Boarman2003). Such concerns suggest that funda-mental changes in how we manage agri-cultural, recreational, and urban environ-ments may be necessary to control theeffects of growing raven populations. ◗

References citedBoarman, W. I. 2003. Managing a subsidized pred-

ator population: reducing Common Raven pre-dation on desert tortoises. EnvironmentalManagement 32: 205-217.

Boarman, W. I., and B. Heinrich. 1999. CommonRaven (Corvus corax). In A. Poole and F. Gill[Eds.], The Birds of North America, No. 476. TheBirds of North America, Inc., Philadelphia, PA.

Kelly, J. P., K. L. Etienne, and J. E. Roth. 2002.Abundance and distribution of the CommonRaven and American Crow in the San FranciscoBay Area, California. Western Birds 33: 202-217.

Roth, J. E., J. P. Kelly, W. J. Sydeman, and M. A.Colwell. 2004. Sex differences in space use ofbreeding Common Ravens in western MarinCounty, California. Condor 106: 529-539.

Sauer, J. R., J. E. Hines, G. Gough, I. Thomas, andB. G. Peterjohn. 1997. The North Americanbreeding bird survey results and analysis.Version 96.4. Patuxent Wildlife Research Center,Laurel, MD.

their nest site and the heronry (see articleon page 3).

In general, ravens were more likely tooccupy heronries after 10 AM and before3 PM. This suggests possible early morn-ing foraging for other available food,such as road kills, or improved opportu-nities for nest predation with middaydeclines in colony attendance by adultherons and egrets. In contrast, WestMarin Island ravens were present contin-uously through the day, spending little orno time patrolling other areas for food.They were also more likely to occupycolony positions below the nest-treecanopy in early morning, perhaps forag-ing for fallen chicks. However, the overallrisk of nest predation in heronries wasbest revealed by the prevalence of ravenactivities (such as number of landings)—not by how often ravens were present.

Predation of Great Egret nests wasmost likely early in the post-guardianperiod, when parents are absent andnestlings can be taken easily by ravens(Figure 3, page 2). Interestingly, thetiming of nest predation by ravens atPicher Canyon did not differ from thatmeasured for 1968–1979 (Pratt andWinkler 1985), when ravens were notpresent (P > 0.91). So the timing of nestpredation reflects a general pattern ofvulnerability rather than the timing ofraven predation per se.

Most observers have noticed thatravens are now present throughout ourregion and that their overall numbersare increasing. But our closer look atraven behavior suggests that weshould be cautious about assumingincreases in nest predation in heron-ries. On the other hand, where ravens

have been present for only a few to sever-al years, nest predation might increasewith continuing declines in neophobia.To further complicate things, whetherravens add to, displace, or buffer nest pre-dation by other species remains a mys-tery. As a result, the extent to whichravens occupy heronries may not closelyreflect predation risk.

For those who watch the lives ofravens with particular interest, it shouldbe no surprise that their behavior chal-lenges as well as inspires our understand-ing of nature. In assessing the risk ofraven predation, herons and egrets as wellas human observers should look beyondthe mere presence of these prominentpredators. ◗

Omnipresence, from page 2

Color-banded Common Raven at Abbotts Lagoon, PointReyes National Seashore.

PH

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the ARDEID 2004

In 1930, near the University of Califor-nia Berkeley campus, an alien invaderescaped from a government-sponsored

genetics experiment. Although theescapee was a genetically natural (notgenetically modified) species, created byevolution, its escape into a new land hashad serious consequences to the naturalinhabitants of our region. In the decadessince, the green monster has spread qui-etly, wiping out resident flora and faunaas it invades, and is now on the verge oftaking over much of western MarinCounty. The invader is a South Africangrass named Ehrharta erecta, and thisarticle tells the story of Audubon Canyon

Ranch’s efforts to understand and defendagainst its spread.

Ehrharta erecta is a highly invasiveperennial grass native to South Africa.The species was part of an experiment atthe U.C. Berkeley botanical garden inves-tigating whether increasing chromosomenumbers increases invasive ability; as itturns out, Ehrharta erecta was tremen-dously invasive without any alterationwhatsoever. By 1950 the species wasabundant at the U.C. Berkeley campus,and in 1996 the tremendous abundanceof Ehrharta erecta in San Francisco natu-ral areas compelled recognition of thespecies as a major conservation concern(Sigg 1996). Ehrharta erecta is currently

invading western Marin, with large popu-lations in Olema Valley, along thePanoramic Highway on Mt. Tamalpais,around the towns of Inverness andBolinas, and in Audubon Canyon Ranch’sBolinas Lagoon Preserve.

Ehrharta erecta is a prolific seed pro-ducer, and the small seeds likely are car-ried to new sites via soil on shoes, on deerhooves, and as contamination in pottedplants. Ehrharta can thrive in an extreme-ly wide range of habitats, from coastaldunes to closed-canopy forest, and formsrobust monospecific stands under full sunor in as little as 2.5% of daylight (Haubensakand Smyth 2000). Once established, popu-lations increase rapidly and Ehrharta

ACR’s Bolinas Lagoon Preserve as a test area for regional conservation

Eliminating Ehrhartaby Daniel Gluesenkamp

Ehrharta erecta. Ehrharta covering native habitat. Pike County Gulch.

Cryptosphere—even thename given to the soiland leaf litter environ-

ment is laced with the promiseof discovery. What creaturesinhabit this hidden world?Strange primitive insects with-out wings (some withouteyes), springtails (named fortheir anal appendages calledfurcula that propel themthrough soil pore spaces),nematodes, thousands ofspecies of mites, feather-

winged beetles, and larvalinsects of all sorts, to name afew. The diversity and com-plexity of the cryptosphere hasbeen compared to coral reefsand tropical rainforests. Andyet, we know very little aboutit.

As mentioned in theaccompanying article,Ehrharta erecta creates adense thatch of vegetationboth above and belowground, thereby altering the

environment’s physicalattributes. The dense swardof green grass sweeping upACR’s Pike County Gulch isan obvious result of Ehrhartainvasion. Impacts of theinvader on soil chemistry andbiotic communities areunknown. While it is not fea-sible at present to perform adetailed study, one piece ofthe Ehrharta experimentinvolves collecting data onleaf litter invertebrates in an

attempt to understand theimpact of the invasive grasson soil fauna.

Hidden ecologies

One square meter of fer-tile soil can containmore individual organ-

isms than all the humans thathave ever lived. Various stud-ies have reported up to 1012

bacteria (1 trillion), 1012 proto-zoa, 107 nematodes, spring-tails and mites, 107 insects,

Ehrharta Underground: There’s more to an invasion than meets the eye by Gwen Heistand


immediate action is required to preventEhrharta from expanding, merging, andsmothering the natural diversity of thissingular preserve.

Three lines of defense

In 2003 ACR’s Habitat Protection andRestoration (HPR) Program initiatedan ambitious project to address the

threat posed by this aggressive invader.The project includes (1) scientificresearch targeted to identify techniquesfor controlling Ehrharta erecta; (2) eradi-cation of Ehrharta on ACR lands; and (3)collaborating with other groups and landmanagers to develop regional solutionsto the Ehrharta invasion.

In June 2003 we began an experimen-tal assessment of Ehrharta removal tech-niques. The experiment compares threepromising techniques: manual removalby pulling, dilute herbicide treatment,and solarization (covering with blackplastic). Each treatment is applied to 10Ehrharta-dominated plots. Data collect-ed from this experiment will allow us todetermine which Ehrharta removal treat-ment is most effective and to evaluatehow each treatment influences recoveryof the natural communities that we aretrying to restore.

In addition to the 30 experimentalplots designed to evaluate removal tech-niques, the Ehrharta experimentincludes two different sets of unmanipu-lated controls with 10 plots each,Ehrharta-dominated plots and un-invaded plots. In each of the 50 plots, weare quantifying the abundance ofEhrharta, vegetation composition, theabundance of native plants and of other

becomes the dominant herbaceous plant,excluding native and non-native vegeta-tion (McIntyre and Ladiges 1985). Thereare currently no established techniquesfor controlling the plant or for restoringinvaded habitat (Pickart 2000).

We have recently discovered severalpatches of Ehrharta erecta in each of thethree canyons that comprise ACR’sBolinas Lagoon Preserve. While most ofthe patches are still small, the Ehrhartainfestation in Pike County Gulch provides

a glimpse at onepossible future forACR’s flagship pre-serve: nearly 2000m2 of the canyonfloor is coveredwith a densemonospecificsward, and thebright greeninvader is climb-ing the sides of thecanyon into thebrown leaf litter ofthe natural herba-ceous understory.Given the plant’samazing rate ofspread and abilityto thrive in arange of habitats,

Ehrharta removal plot. Uninvaded versus invaded habitat.

Figure 1. After one year, all three treatments significantly reduced the percentcover of Ehrharta erecta, relative to the invaded control plots, while manualremoval also stimulated germination from the seed bank (see text). Solid barsindicate the percent of plots covered by Ehrharta; error bars indicate one stan-dard error (P < 0.001).

continued on page 8

1,000 earthworms,and 20,000 km offungal mycelia.(Neher 1999,Pennisi 2004).Bacteria, fungi,and nematodesare three of thetaxonomic groupsthat have the lowestpercentage of describedspecies, making classificationof soil communities difficult atbest. In addition, within eachtaxonomic group, somespecies feed on bacteria, some

on fungus, someon roots, and

some on otherinvertebrates.Where stud-ied, differentecosystem

types havebeen found to

support differentassemblages of soil

biota. Grasslands have showna marked abundance ofomnivorous soil invertebrates.Agricultural soils can havegreater numbers of bacterial

feeders and root-feedingnematodes. Forests display arelative abundance of fungalfeeders (Neher 1999).

Belowground food websand ecological relationshipsare intricate and intimatelylinked to the abovegroundenvironment (Wardel et al.2004, Wardel 2002). Science isjust beginning to delve intothese connections. Few stud-ies have attempted to assesssoil biota in relation to eitherhabitat restoration or invasivespecies. Invasion of non-

native plants may affect aboveand belowground feedbacks,potentially changing soilchemistry and altering soilbiota to facilitate invasion (vander Putten 2002).

Hidden consequences?

During Februarythrough April of 2004,Dan and I worked with

several volunteers to collect350 1-cm2 litter samples fromthe center of each of the 50experimental plots used in theErharta study. Each sample

the ARDEID 2004

non-native invaders, important habitatcharacteristics, and leaf-litter inverte-brate communities.

Preliminary results indicate that aweak herbicide solution is most effectiveat reducing Ehrharta abundance, while

manual removal actually stimulatesEhrharta seed germination and increasesabundance of the invader (Figure 1).While Year One results show solarizationto be moderately effective at reducingEhrharta cover, some adult Ehrharta

plants are able to sur-vive beneath the plastictarp; the utility of thistechnique will dependon how well these sur-vivors recover in thenext year.

Ehrharta controlmay further depend onlimiting the ability ofEhrharta populationsto recover from buriedseeds, so we are experi-mentally assessing seedlongevity by buryingsmall bags of seeds attwo depths, exhumingseedbags at regularintervals, and germi-nating the exhumedseeds to determineseed survival. Twelve

bags were buried at each of 10 locations,and the first set of bags will be exhumedand tested for viability in November 2004.Early observations of buried seed bagsprovide reason for hope. Each of themarker stakes is surrounded by a constel-lation of small clusters of Ehrhartaseedlings, one cluster for each seed bag!This shows that the germination rate ofthese buried seeds is very high and thatrelatively few seeds remain dormant, andsuggests that control efforts may not haveto contend with a large and persistent soilseedbank.

Although the increasing ground coverby Ehrharta clearly reduced the cover ofnative plants (Figure 2), recovery of nativeplants one year after treatment did notdiffer significantly among treatments.However, differences in native coveramong treatments may become signifi-cant as the small native plants mature.

Probably the most interesting variablethat we will be monitoring is the responseof leaf-litter invertebrate critters (seeaccompanying article). Very few scientificstudies have quantified the impacts ofplant invasion on animal communities,and only a handful have assessed howanimal communities are affected by inva-sive plant control efforts. Terrestrial inver-tebrates are extremely important, both aselements of decomposition and nutrientcycles and as the basis of many terrestrialfood webs, and ACR’s Ehrharta researchwill be one of only a few studies thatassess how the terrestrial invertebratecommunity is affected by non-nativeplant invasion. It will be extremely inter-esting to observe how invertebratesrecover following Ehrharta removal!

While the scale of Bolinas LagoonPreserve’s Ehrharta invasion is daunting,

Figure 2. Native plant cover declines with increasing cover by Ehrhartaerecta. Data are from unmanipulated plots (r2 = 0.59, P < 0.001).

was run through a BerleseFunnel, which uses light todrive soil fauna downwardinto a container, producingapproximately 1/8 to 1/4 tea-spoon of invertebrates.Characterization, on a broadscale, of invertebrate assem-blages in each of these sam-ples has begun. Just to give aflavor of the numbers found inless than a teaspoon, one sam-ple currently being analyzedcontains 187 acari (mites), 214collembolans, 3 dipterans(flies), 12 coleopterans (bee-

tles), 13 diplurans (primitivewingless insects), and 11unidentified larvae—withapproximately two-thirds ofthe sample still to be sorted!

Once all samples have allbeen processed, we will ana-lyze the results to determinewhether there is any differ-ence in soil fauna between thethree treatments (herbicide,solarization, and manualremoval) as well as betweenthe invaded control sites anduninvaded plots. We mightexpect to see more omnivores

in the grass dominated plotsversus more fungal feeders inthe native forest understory.Plots covered in black plasticmight be expected to have adifferent suite of creaturesduring and immediately aftertreatment. One aspect of whatwe are hoping to ascertain ishow resilient the ecologicallyimportant leaf litter commu-nity is in response to restora-tion efforts. Because so little isknown about soil ecology onACR lands, whatever we dis-cover will be exciting. These

data, combined with data onthe abundance Ehrharta andother non-native and nativeplant species, as well as datacharacterizing plant speciescomposition for each plot,should advance our under-standing of how Ehrhartaerecta control, eradication,and dispersal might affectnative biota.

On a more personal note,it is difficult to describe thethrill of seeing a microscopicfly with beaded antennae andperfectly formed halteres or a

Ehrharta plot. Buried seed bag sprouting (Ehrharta in circles).

our commitment to protecting the pre-serve’s natural diversity mandates that weact to restrain this harmful invader. In thelast year we have conducted surveys tolocate and map all ACR Ehrharta patchesand have begun work to treat the highpriority sites. ACR has followed a “stitch intime” policy with regard to control work,focusing on small easily- eradicatedpatches of Ehrharta that have the poten-tial to become intractable infestations.Results of this first year have been prom-ising, and we expect that several years ofconcerted effort by staff and volunteerswill be required to control this advancedinvasion.

Invasive species such as Ehrharta erec-ta do not recognize property boundaries,and so we are working with our neigh-bors and with other restorationists toimprove Ehrharta management acrossthe region. In the last 18 months, ACRstaff have helped make the Marin-Sonoma Weed Management Area (WMA)aware of the threat posed by Ehrhartainvasion, and as a result the WMA con-tributed significant support to imple-menting ACR’s Ehrharta experiment and

assigned 2 interns to map all Ehrhartaoccurrences in Marin County. As ACR’sHPR Specialist, I communicate frequent-ly with biologists from California StateParks, the National Park Service, andother agencies to share information andinsights regarding Ehrharta manage-ment. When ACR’s Ehrharta experimentis completed we will use the data todevelop a prescription for restoringEhrharta-invaded habitat, and we expectthat presentation of results will furtherincrease regional Ehrharta controlefforts.

Conservation commitment

The genus Ehrharta is largelyrestricted to the Cape region ofSouth Africa, which, like California,

is one of 5 regions on the planet with aMediterranean climate. Ehrharta erectahas the greatest geographic range of anyplants in the genus, and it is interesting tothink that Ehrharta erecta may, by itsnature, be a colonizer of new sites. In amanner reminiscent of many ofCalifornia’s most marvelous natives, thetaxon named Ehrharta erecta emerged inan accelerated burst of speciation stimu-lated by the appearance of summer-aridclimate in southern Africa. Ehrharta erec-ta is not a “bad” plant but, rather, is anamazing and tremendously vital organ-ism that is the singular result of a uniqueevolutionary history. Unfortunately, itsaggressive spread in coastal Californiathreatens to eliminate some survivingrepresentatives of California’s own uniqueevolutionary history.

Harmful invaders like Ehrharta posevery significant challenges, but they alsoprovide important opportunities.Research on invasive species is helping us

understand how natural systems workand is creating a fruitful nexus of collabo-ration between “pure” scientists and“applied” restorationists. The urgent needfor research and restoration volunteershas fueled a joyful reconnection of citi-zens with nature that is similar to theamateur scientist revolution of 19th cen-tury England. Most importantly, the ubiq-uity and impact of biological invasions ishelping humans realize that they must beactive and conscientious stewards of thisplanet: where Rachel Carson’s SilentSpring demonstrated that human actionscan have global impacts, the replacementof a diverse natural community by a sin-gle species of grass is teaching us thatinaction is not without consequences.

Over decades and centuries, Ehrhartaerecta may or may not accumulate newpathogens and herbivores and become awell-regulated and harmless part of ourcoastal plant communities. In the mean-time, conservation organizations such asACR remain committed to defendingCalifornia’s ancient natural diversity fromthe negative impacts of Ehrharta erectaand other runaway invaders. ◗

References citedHaubensak, K. and A. Smyth. 1999. Erharta erecta.

Species assessment prepared for ChannelIslands National Park.

McIntyre, S. and P. Y. Ladiges. 1985. Aspects of thebiology of Erharta erecta. Lam. Weed Research25: 21-32.

Pickart, A. J. 2000. Ehrharta calycina, Erharta erec-ta, and Ehrharta longifora. In: Bossard, C. C., J.M. Randall, and M. C. Hoshovsky (eds): Invasiveplants of California wildlands. University ofCalifornia Press, Berkeley, CA.

Sigg, J. 1996. Erharta erecta: sneak attack in themaking? California Exotic Pest Plant CouncilNews 4(3):8-9.

beetle larva with a wildlyintricate exoskeleton thatlooks like it is made from tor-toise shell or the field of viewunder a dissecting scopecompletely filled with mites ofdifferent sizes and shapes.Knowing that these creatureslive their lives navigating thepore spaces in the soil or theunderside of decomposingleaves adds to my amaze-ment at the intricacy of lifeon this planet. And, alongwith the sheer aestheticpleasure of viewing these

spectacular, minute beingsand a feeling of increasedrespect for all that livesunderfoot, I can’t help butwonder what we may bedoing to alter this world aswe move invasive speciesaround the globe and prac-tice less than sustainablemethods of agriculture. ◗

ACR is extremely fortunate tohave a crew of committed, andpossibly slightly crazy, volun-teers who share this sense ofrespect and adventure and

who enjoy spending Saturdaysand Sundays bent over micro-scopes keying out and countingwee beasties found in the cryp-tosphere. Many thanks go toTom Bradner, Anna-MarieBratton, Judy Dugan, AnnMintie, and Tony Paz.

References citedNeher, D. A. 1999. Soil community

composition and ecosystemprocesses: comparing agriculturalecosystems with natural ecosys-tems. Agroforestry Systems 45:159-185.

Pennisi, E. 2004. The secret life offungi. Science 304: 1620-1622.

van der Putten, W. H. 2002. How tobe invasive. Nature 417: 32-33.

Wardle, D. A., R.D. Bardgett, J.N.Klironomos, H. Setala, W.H. vander Putten, and D.H. Wall 2004.Ecological linkages betweenaboveground and belowgroundbiota. Science 304: 1629-1633.

Wardle, D. A. 2002. Communitiesand Ecosystems: Linking theAboveground and BelowgroundComponents. PrincetonUniversity Press, Monographs inPopulation Biology.

Volunteers set up the experiment.


the ARDEID 2004

The North Pacific Coast Railroadconstructed a levee along theTomales Bay shoreline in the 1870s

that modified the hydrology of east-shoremarshes. Although wooden trestles werebuilt across major tide channels, watercirculation was altered and sedimentbegan to accumulate behind the levees.Livermore Marsh at the Cypress GroveResearch Center is one of these wetlandsthat exhibit some interesting physical andbiotic characteristics. Before AudubonCanyon Ranch (ACR) purchased the prop-erty in 1971, previous owners installedfloodgates in the levee so they could usethe 26-acre wetland for grazing and fresh-water storage. In 1982, the levee waseroded by El Niño flood waters. ACRdecided to repair the levee and constructa spillway at an elevation that would pre-vent tidewater from entering LivermoreMarsh. ACR excavated four ponds in thelower marsh to maintain coveted fresh-water habitat during dry seasons.However, when the levee breached byflood waters again in 1998, ACR decidedto allow the wetland to be restored natu-rally to a tidal marsh system.

In 1999, grants from the Frank A.Campini Foundation and the MarinCommunity Foundation allowed ACR torestore trail access across the levee breachand to conduct a five-year study to docu-ment physical and biotic changes associ-ated with the reintroduction of tidal cir-culation. In recent issues of The Ardeid,we presented reports summarizing ourresearch objectives (1999), watershedeffects (2001) and changes in bird use(2003). This article examines principalfactors influencing the shape (topogra-phy) of the lower marsh (Figure 1).

The physical characteristics of tidalmarshes have been studied extensivelyaround the world, and some of the mostimportant research on the morphology ofdiked salt marshes has been conducted inthe San Francisco Bay area (Coats etal.1989; Coats and Williams 1990, andWilliams and Orr 2002). These engineershave identified correlations between key

marsh features,such as channeldimensions andtidal exchange,that are oftenused to designmarsh restora-tion projects. Wemeasured thesame topograph-ic features todocumentchanges duringthe transforma-tion of LivermoreMarsh from afreshwater to atidal system.

This studyincluded month-ly measurementsof the tidal inlet,annual surveysof developingtide channels,and two detailedtopographic sur-veys of the lowermarsh in 1999 and 2003 (see photo onback cover). Hydrologist LaurenHammack used these data to estimatefour characteristics of tidal marsh sys-tems: tidal inlet area, active tide channellength, active tide channel volume, andtidal prism volume (Table 1, page 12). Thetidal prism estimate represents the vol-ume of tide water that flows through thelevee below the elevation of the meanhigher-high water (3 ft NGVD29, or 5.4 ftNOS based on NOAA predictions).

Tidal versus fluvial effects

Tidal processes and terrestrial riverflow are important factors thatshould be evaluated before apply-

ing scientific models to particular sites.This is a complex and demanding chal-lenge, but at Livermore Marsh, we hadthe advantage of being able to routinelyand accurately monitor changes in theinlet area. We used a laser level mountedat either end of the bridge to provide a

stable reference for depth measurementsat 47 locations across the 96-ft bridge.

One of the interesting questions we areexploring is whether different types oftidal patterns have predictable effects onthe cross-sectional area of the tidal inlet.“Neap” tides exhibit the minimum rangebetween high and low tides, while“spring” tides exhibit the largest rangebetween highs and lows. “Median” tidesrange between mean-higher-high water(MHHW) and mean-lower-low-water(MLLW) and occur for several daysbetween the neap and spring tide cycles.

I measured the inlet each month dur-ing the last day of a median tide cycle andscheduled neap and spring measure-ments at least three times a year. We weresurprised to find that tidal action did notsignificantly influence either the cross-sectional area of the inlet or the rate ofchange in the inlet area.

From our analysis, it appears thatcumulative rainfall was the primary factor

Figure 1. Elevations associated with tidal inundation at Livermore Marsh, in 2003.

Influences on the hydro-geomorphology of Livermore Marsh

The Power of Rainfallby Katie Etienne

influencing changes in the inlet area(Figure 2). In addition, the effects of rain-fall were not significantly influenced bytide conditions. Figure 3 illustrates thehigh variability in the size of the tidal inletduring the first five years, although theinlet area appears to be stabilizing aroundthe values predicted from mature marshsystems (see The Ardeid 2002).

The role of sediment

We calculated the volume of pri-mary and secondary tide chan-nels, as well as incipient chan-

nels that may eventually become tertiarychannels or blind sloughs. During the firstyear after the levee breach, the primarychannel increased in length by 128 ft. Theprimary tide channel did not lengthenbetween 1999 and 2000, but there was asmall increase in channel volume as thechannel became deeper and wider. Thispattern of channel lengthening followedby widening is consistent with otherdeveloping marshes where changes inwidth are also more rapid than changes indepth (Coats et al. 1995).

Although there was an increase inchannel length and volume in 2001 thatcontributed to the increase in tidal prism,the tidal inlet continued to fill in (Table1). This inverse relationship betweenchanges in the tidal prism and the inlet isdifferent from the direct relationship inmature marsh systems, where increasedinlet area corresponds to increased tidalprism volume (Coats et al. 1995).

Subsequent channel surveys indicatedthat although most channels were becom-ing wider and longer, the total channelvolume and tidal prism decreased in 2002.However in 2003, we measured a largeincrease in channel volume and length as

well as an increase in tidal inlet area(Table 1). These episodic changes inchannel development are probably asso-ciated with rainfall events and the cohe-sive nature of the sediment, which tendsto erode in blocks.

In 1999, Gian-Marco Pizzo identifiedthe significance of the dense substrate,which is not easily eroded by runoff ortidal action. His calculation of tidal veloc-ity in the primary channel (0.2 m/sec)was far less than the 1 m/sec normallyrequired to cause erosion. Pizzo conclud-ed that channel development in Liver-more Marsh was primarily influenced bythe propagation of vertical head cuts thatproduce the stair-step shape in develop-ing channels. During the next five years,we continued to document the lateralmovement of numerous head cuts andslumping banks. Over time, head cuts andchannel banks became taller and themusic of falling water became louder asturbulent flow scoured material awayfrom the base of new waterfalls.

Sporadic changes in tidal prism

Prior to analysis, we partitioned thetopographic survey data to distin-guish between active tide channels

and isolated or “perched ponds” that didnot drain during diurnal tidal cycles(Figure1). The small circular pond closestto the levee is one of four ponds con-structed in 1983, when ACR was manag-ing the system as a freshwater marsh. Thelarger, crescent-shaped pond is a remnantof a pre-existing channel that wasmapped by the U.S. Coast Survey inthe1862 (see The Ardeid, 1999). Becausewater level in these and other smallponds in the marsh did not rise and fallwith the tides, we excluded their volumes

from tidal prism estimates in 1998through 2001.

The head cut of the primary tide chan-nel progressed very slowly through themiddle of the marsh, compared to chan-nel banks that developed in the perimeterof the marsh. The rate of erosion in themiddle marsh was reduced by a remnantstand of tules, because their dense stemsdecreased water velocity and their rhi-zomes bound the sediment together.Another factor was probably the percola-tion of water from the perched pond,which maintained soil saturation in themiddle of the marsh. Saturation withwater prevented cracking of the substratethat allows blocks of sediment to tip andfall downstream.

Meanwhile, channel banks around theperimeter of the marsh continued to col-lapse into the channel, and sediment wasslowly transported through the system.Finally, after several weeks of heavy rainand the spring tide cycle of 6-8 Jan 2004,the sill between the crescent pond andthe head cut eroded, and water previouslystored in the large pond was released(Figure 4). As rain continued to fall, hightides began to circulate through the cres-cent pond, which increased the tidalprism by at least 0.36 acre-ft. This esti-mated increase does not include the addi-tional tidal volume resulting from the ero-sion of unconsolidated material in thepond by winter runoff and high tides.

This process of slow erosion and tidechannel development indicates theimportance of substrate composition.Another major factor is the elevation ofthe marsh plain. Survey data show thatmost tide water never flows above thedeepest portions of the developing chan-


Figure 2. The tidal inlet area of Livermore Marshincreased significantly with cumulative rainfall (P <0.001).

Figure 3. The tidal inlet area of Livermore Marsh isapproaching predicted values based on studies ofmature levee marshes in San Francisco Bay(square) and Tomales Bay (triangle).

Figure 4. Six years after the levee breach, the tidalprism increased rapidly after the tide channel finallyeroded the sill of the perched pond. The increasedtidal circulation and winter flooding contributed to a28% increase in inlet area between 18 Dec 2003and 7 Jan 2004.

KAT

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TIE

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the ARDEID 2004

nels, and only extreme high tides haveany effect on the surface of the marshplain. This helps explain why salinity inmost areas with restricted tidal exchangetends to remain fresh or slightly brack-ish. From 1998-2003, salinity measure-ments in the crescent-shaped pondremained near 1 ppt, and most of thetide channel was brackish (4.0–9.6 ppt).

The isolated pond near the levee exceed-ed the salinity of Tomales Bay duringsummer months. These salinity differ-ences reflect the importance of marshplain elevation, which continues torestrict tidal influence.

The dominant factors influencing theearly development of Livermore Marshwere fluvial action, sediment characteris-tics, and marsh plain elevation. We antici-pate the effect of tidal action on physicaland biological processes in the marsh willdepend upon future rates of sedimenttransport and sea level rise. ◗

References citedCoats R.N., M. Swanson, and P. B. Williams. 1989.

Hydrologic analysis for coastal wetland restora-tion. Environmental Management 13(6):715-727.

Coats, R.N., and P. Williams. 1990. Hydrologictechniques for coastal wetland restoration illus-trated by two case studies. P. 236-246 in J.J.Berger editor, Environmental Restoration: sci-ence and strategies for restoring the earth.Island Press, Washington, D.C.

Coats, R.N., P.B. Williams, C.K. Cuffe, J.B. Zedler, D.Reed, S.M. Waltry, and J.S. Noller. 1995. Designguidelines for tidal channels in coastal wet-lands. Philip Williams and Associates, SanFrancisco, CA.

Williams, P. B. and M.K. Orr. 2002. Physical evolu-tion of restored breached levee salt marshes inthe San Francisco Bay Estuary. RestorationEcology 10(3):527-542.

Year Inlet area1 Tide channel Active tide channel2 Tidal prism(ft2) length (ft) (acre-ft) (acre-ft)

1998 283 230 0.32 1.41999 176 420 0.40 2.32000 94 420 0.44 2.62001 62 560 0.52 2.82002 32 712 0.46 2.42003 95 770 0.56 2.72004 127 1170 0.92 3.1

1 below 3 ft NGVD292 below 1.5 ft NGVD29

Table 1. Changes in the geomorphic characteristics of Livermore Marsh (1998-2004) show a continuingincrease in channel length and tidal prism volume, but fluctuations in channel volume and inlet area(2002-2003).

Visting investigators

Effects of invasive species on nitrogen reten-tion and other issues in the ecology andrestoration of coastal prairie. Jeff Corbinand Carla D’Antonio, UC Berkeley.

Carnivore use of riparian corridors in vine-yards. Jodi Hilty, UC Berkeley.

Multi-scaled vegetation data to predictwildlife species distributions using a wildlifehabitat relationship model. JenniferShulzitski, USGS Golden Gate FieldStation.

Impact of butterfly gardens on pipevine swal-lowtail populations. Jacqueline Levy, SanFrancisco State University.

The effect of landscape changes on nativebee fauna and pollination of native plantsin Napa and Sonoma counties. GretchenLeBuhn, San Francisco State University.

Ecological indicators in West Coast estuaries.Steven Morgan, UC Davis BodegaMarine Lab; Susan Anderson, UC SantaBarbara; and numerous collaborators.

Consequences of species invasion underglobal climate change. Elizabeth Brusati,UC Davis.

Community based assessment of biologicalhealth of riparian wetlands in the SonomaCreek watershed. Caitlin Cornwall,Sonoma Ecology Center.

Water quality monitoring at several points inTomales Bay, including ACR’s WalkerCreek delta. Lorraine Parsons, PointReyes National Seashore.

Bird communities in North Coast oak-vine-yard landscapes. Emily Heaton, UCBerkeley.

Factors causing summer mortality in Pacificoysters. Fred Griffin, Bodega MarineLab.

Effects of sudden oak death-induced habitatchange on vertebrate communities. KyleApigian and Don Dahlson, UC Berkeley.

The differential invisibility of annual andperennial grasslands in California by anon-indigenous invader, Foeniculum vul-gare. Joel Abraham and Jeff Corbin, UCBerkeley.

Differences in arthropod community composi-tion in native and exotic dominated grass-lands. Natalie Robinson, UC Berkeley.

A comparison of carbon cycling and materialexchange in grasslands dominated bynative and exotic grasses in NorthernCalifornia. Laurie Koteen, UC Berkeley.

Black Brant counts at Drakes Estero, TomalesBay and Bodega Bay. Rod Hug, SantaRosa, CA.

Monitoring Avian Productivity and Survivor-ship (MAPS) station at Livermore Marsh.Denise Jones, Institute for BirdPopulations.

Tidewater goby inventory for Tomales Bay.Darren Fong, GGNRA.

Conservation concerns for Cordylanthusmaritimus ssp. palustris. Todd Wilms,Emeryville, CA.

Strophariaceae of California. Peter Wernerand Dennis Desjardin, San FranciscoState University.

North Bay counties heronand egret project ◗Annualmonitoring of reproductiveactivities at all known heronand egret colonies in fivenorthern Bay Area countiesbegan in 1990. The data areused to examine regionalpatterns of reproductiveperformance, disturbance,habitat use, seasonal timingand spatial relationships amongheronries. The project hasbeen recently incorporated intothe Integrated RegionalWetland Monitoring (IRWM)program, a pilot project todevelop regional monitoring forSan Francisco Bay. We arecurrently preparing anannotated atlas of regionalheronries.

Picher Canyon heron/egret project ◗The fates ofall nesting attempts at ACR’sPicher Canyon heronry aremonitored annually, based onprocedures initiated by HelenPratt in 1967, to track long-term variation in nestingbehavior and reproduction.

Livermore Marsh ◗AsACR’s Livermore Marsh, onTomales Bay, transforms froma freshwater system into atidal salt marsh, we arestudying the relationshipbetween increasing tidal prismand marsh channel develop-ment. Monitoring of winter andbreeding bird use began in1985. The data will be linked tomeasurements of vegetationto reveal changes associatedwith the developing tidalmarsh. We also monitor thedepth and duration of groundwater which strongly influ-ences biological conditions inthe upper marsh.

Newt population study ◗Annual newt surveys havebeen conducted along theStuart Creek trail at BouveriePreserve since 1987. Theresults track annual andintraseasonal abundance, andsize/age and spatial distribu-tions along the creek.

In progress:project updates

Tomales Bay Shorebirds ◗Since 1989, we have conductedannual baywide shorebirdcensuses on Tomales Bay.Censuses involve six baywidewinter counts and onebaywide count each in Augustand April migration periods. Ateam of 15-20 volunteer fieldobservers are needed toconduct each count. The dataare used to investigate winterpopulation patterns of shore-birds, local habitat values, andconservation implications.

Tomales Bay waterbirdsurvey ◗ Since 1989-90,teams of 12-15 observers haveconducted winter waterbirdcensuses from survey boatson Tomales Bay. The resultsprovide information on habitatvalues and conservation needsof 51 species, totaling up to25,000 birds. Future work willfocus on trends and determi-nants of waterbird variation onTomales Bay.

Predation by ravens inheron/egret colonies ◗ Wehave been observing ravens inMarin County and measuringraven predatory behaviors atheron and egret nestingcolonies. The field workinvolves radio telemetry andbehavioral observations. Wehave produced scientificpapers on the status of ravensand crows in the San FranciscoBay area, patterns of homerange use, and raven predatorybehaviors in heronries.

Experimental assessmentof Wild Turkey impacts ◗Invasive Wild Turkeys arecommon at Bouverie Preserveand throughout most ofSonoma County. DanGluesenkamp is measuring theeffects of ground foraging byWild Turkeys on vegetation,invertebrates, and herpeto-fauna in the forest ecosystemof Bouverie Preserve. Theresults will and provideinformation that can be used toimprove management andcontrol of turkey populationsby agencies.

Ehrharta erectamanagement andresearch ◗ Erharta erecta is ahighly invasive perennial grassnative to South Africa. It iscurrently invading west MarinCounty and is abundant inACR’s Pike County Gulch. Thegoals of this project are tounderstand the effects ofEhrharta invasion, developtools for control of Erharta, andrestore habitat invaded byErharta at Bolinas LagoonPreserve.

Olema Marsh bird census◗ Although considerable birdcensus work was conducted atACR’s Olema Marsh in the1980s and early 1990s, recentinformation on bird use isneeded to include OlemaMarsh in the Point ReyesNational Seashore GiacominiWetland Restoration Project.Methods involve point countsand distance sampling,conducted by Rich Stallcup.

Plant species inventory ◗Resident biologists maintaininventories of plant speciesknown to occur along theTomales Bay shoreline, and onACR’s at Bouverie and BolinasLagoon preserves.

Cape ivy control,Volunteer Canyon ◗ Workconducted by Len Blumin hasproven that manual removal ofnonnative cape ivy cansuccessfully restore riparianvegetation. Continued vigilancein weeded areas of ACR'sVolunteer Canyon has beenimportant, to combat resproutsof black nightshade, Vinca, andJapanese hedge parsely.

Annual surveys andremoval of non-nativecordgrass ◗ Protection ofACR’s shoreline propertiesfrom invasion by nonnativeSpartina species is critical tothe protection of ACR landsand provides a criticalcontribution to the overallmonitoring and managementof Tomales Bay and BolinasLagoon. In addition to conduct-ing surveys on ACR lands,Katie Etienne is collaboratingon surveys of other shorelineproperties in these estuaries.

Vernal wetland botanicalsurveys at BouveriePreserve ◗ As part of ouroverall effort to determine theecological values of vernalwetlands at Bouverie Preserve,botanist Ramona Robisonconducted floristic surveysdesigned to target rare plants.The surveys provide plantspecies lists, vegetation covervalues for each species, andexact (GPS) delineation ofwetland habitats and locationsof rare plants.

Salmarsh ice plantremoval ◗ Non-native iceplant is being removed frommarshes and upland edges atToms Point on Tomales Bay,using manual removal, shadingwith black plastic, and glypho-sate. The goals are to eliminateinvasive ice plant from TomsPoint and to collaborate withother land managers toremove ice plant from othersites in Tomales Bay.

Eradication of Elytrigiapontica spp. pontica ◗Elytrigia is an invasive, non-native perennial grass thatforms dense populations withnearly 100% cover in seasonalwetland sites. We are usingmanual removal by groups ofvolunteers, light starvation andsolarization using black plastictarps, and glyphosate spottreatments.

Eucalyptus removal ◗Eucalyptus trees are beingremoved, with incrementalannual cutting, from ACR’sBolinas Lagoon Preserve, andalong the Highway 12 borderof Bouverie Preserve. DanGluesenkamp is conducting anexperiment to determine theoptimal method for controllingEucalyptus resprouts.

Wood Duck boxes ◗ RichStallcup has installed andmaintains several Wood Ducknest boxes along Bear ValleyCreek in ACR’s Olema Marsh.

Bluebird boxes ◗ TonyGilbert has installed fourbluebird boxes in the CypressGrove grasslands with theobjective of providing nestsites for two pairs of WesternBluebirds.


Ardeid (Ar-DEE-id), n., refers to

any member of the family

Ardeidae, which includes herons,

egrets, and bitterns.

The Ardeid is published annually by Audubon Canyon Ranch as an offering to field

observers, volunteers, and supporters of ACR Research and Resource Management.

To receive The Ardeid, please call or write to the Cypress Grove Research Center.

Subscriptions are available free of charge; however, contributions are gratefully

accepted. ©2004 Audubon Canyon Ranch. Printed on recycled paper.

Managing Editor, John Kelly. Layout design by Claire Peaslee.

AUDUBON CANYON RANCH IS A SYSTEM OF WILDLIFE SANCTUARIES

AND CENTERS FOR NATURE EDUCATION

BOLINAS LAGOON PRESERVE • CYPRESS GROVE RESEARCH CENTER • BOUVERIE PRESERVE

the

Ardeid

Research

and Resource

Management at

Audubon Canyon Ranch

Audubon Canyon Ranch

4900 Shoreline Hwy., Stinson Beach, CA 94970

Cypress Grove Research CenterP.O. Box 808Marshall, CA 94940

(415) 663-8203

Nonprofit Org.U.S. Postage

PAIDPermit No. 2

Stinson Beach, CA

Livermore Marsh see page 9

Pacific Land Surveys measured the topography of ACR's LivermoreMarsh during a five-year study of ecological changes associated with

the reintroduction of tidal circulation.

KATI

E ET

IEN

NE

research and resource management at audubon canyon ranch

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