Daijiro Hata

Feeding Habits of SwansFeeding Habits of Swans

http://www.flickr.com/photos/singingfish/259448032/

Characteristics of Swans

• Anseriforms, Anserinae – 8 species.• Large body• Herbivory• Social – make flocks • Migratory waterfowl most of the translocated swans return to the original

places the following year. • Use wetlands for foraging and nesting.

Mute swan

Tundra swan

Trumpeter swan

N American Swans

http://www.bsc-eoc.org/lpbo/swans/swans.html

Food Type of Swans

• 3 types of food 1) Agricultural plants - High carbohydrates 2) Wetland plants - Lower carbohydrates than ag. ｐ

lants - Some high water & high fiber content 3) Animal matter - High protein

Common Name Science Name Place HabitatCygnus olor Old World (Eurasia), introduced in US slowly flowing rivers, lake edges

C. cygnus Old World (Iceland, Europe, Asia) pools, lakes, slow rivers

C. bewickii Old World (Russia, W Europe, E Asia) shallow pools

C. buccinator North America stable, quiet waters of lakes, marshes, sloughs

C. columbianus North America shallow lakes, slow moving rivers, coastal estuaries

C. melancoryphus South America large marsh and lakes

C. atratus Australia, introduced in New Zealand large, permanent lakes

C. sumnerensis extinctNew Zealand swan

Black swan

terrestrial grasses, animal materials, pondweed, waste grain, potatoes

wild celery (Vallisneria), wigeon grass, bulrushes, pondweed, clams, waste grain, potatoes

pondweed, eelgrass (Zostera), terrestrial grass

Whistling swan(tundra swan)

Black necked swan

Mute swan

Whooper swan

Bewick's swan

Trumpeter swan

pondweed, muskgrass, eelgrass (Zostera), green algae (Entermorpha), west grain, terrestrial grasses, animal materials

algae (Nitella), mud plantain (Heteranthera), aquatic insect

pondweed, crowfoot (Ranunculus), arrowhead (Sagittaria)

cattail, algae, wild celery (Vallisneria), pondweed, terrestrial grasses

tubers and seeds of sago pondweed (Potamogeton pectinatus) (Sherwood 1960).

Brazilian waterweed (Egeria densa) (Corti and Schlatter 2002)

Aquatic Plants

• Especially, Pondweed (Potamogeton spp.)

- Swans eat tubers, seeds, ….

- Foraging swans go to find pondweeds. (Earnst & Rothe 2004)

• Others

- Eelgrass or Wild celery (Vallisneria spp.)

- Widgeon grass (Ruppia spp.)

- Muskgrass or Skunkweed (Chara spp.)

Eelgrass or Wild celerySago pondweed

Widgeon grass

Muskgrass or Skunkweedhttp://aquaplant.tamu.edu

http://aquaplant.tamu.edu

Population of Swan

• Population of swans have increased.

- Conservation

- Management for recreation

hunting, watching

- Low enforcement

• Trumpeter swan: Rocky Mountain Pop.

from <200 (1935) to 2200 (1993) . (Baskin 1993, Squires & Anderson 1995)

• Mute swan: Atlantic Flyway Pop.

from 200 (1955) to 5300 (1987), 12600 (1999).

(Conover & Kania 1994, USGS Website 2001)

• Tundra swan: Pacific Flyway Pop.

increased since 1940s, Western 50000(1958),

60000 (2005). (Eastern 100000) (Sherwood 1960, ADFG Website 2005)

Noordhuis et al. 2002.

Mute & Bewick’s swan

(Netherlands)

USGS Website 2001

Mute swan

(Atlantic Flyway)

http://www.pwrc.usgs.gov/resshow/perry/muteswan.htm#Background

Problems of Swans• Population have increased.• Wetlands & habitats have declined.• Make flocks & concentrate in the scarce habitats.• Large, but the limited digestive capacity. (21-34%: Mitchell & Wass 1995) - Eat a lot.

• Wave & Overexploitation of plants - Possible to destroy ecosystem in wetlands. - And compete with other animals.

E Coast & Chesapeake Bay

• Wildlife managers say…Tundra swan

1) Significant damage to aquatic plants.

2) Conflict with other shorebirds.

• Once MBTA (Migratory Bird Treaty Act) did not distinguish b/w native and non-native bird.

• But, congress revised MBTA to exclude non-native birds in 2004.

Migratory Bird Treaty Act

• Implemented treaties with Great Britain for Canada ratified in 1919, and Mexico 1936.

• For the protection of migratory birds and provided for regulations to control taking, selling, transporting, and importing migratory birds.

• This act was an important step in the development of international law.

Mitchell & Wass 1996.

Rees 1990.

•Submersed, emergent, and floating-leaved macrophytes are all subject to substantial grazing losses.

•Many large and small grazers may affect: manatees, muskrats, waterfowl, fish, crayfish, and insects (Lodge 1991).

Grazing

Role of Swans in Wetlands

• Grazing Slow down the succession of wetlands. - Black-necked swan might play an important role as a

regulator of aquatic plant biomass to cause a delay in ecological succession (Corti & Schlatter 2002).

• Bring and drop nutrition in wetlands. - 40% of N and 75% of P in a wetland (Post et al 1998).

• Cultivate wetlands.• Disperse plants and invertebrates.

Habits: Food Availability

• Swans well know the cost/benefit.

- Prefer places with

high food densities & low competition.Swans visit high food density patches at a higher frequency.

Strong negative correlation b/w the number of swan-days and the number of goose- and wigeon-days (reduction in the food supply).

Food supply decrease make smaller flocks and graze at several different sites. (Klaassen et al. 2006).

• Shift the food habit flexibly.

- aquatic plants waste grains.

Shallow Water (Mute swan: In depths <50cm extensive grazing on SAV)

Nolet et al. 2006

Bewick’s swan: max depth is 0.89m, but prefer shallower water like <0.45m.

•From winter to spring

- Potamogeton tubers were highly preferred.

•Summer

- Potamogeton foliage.

- Nestling trumpeter swans prefer Potamogeton spp.

•Chara spp. was eaten in proportion to its availability.

(Squires 1995)

Adverse Results • Black swan population density was closely

correlated with plant biomass.• Although the swan population became as high as

25/ha, direct grazing growth consumption was slight.

• The grazing rate was 0.007/day, by comparison with plant growth rates of 0.06-0.10/day, and loss rates in periods of decline of 0.07-0.18/day.

• Lack of light was far more important than swan grazing for plant decline.

(New Zealand: Mitchell & Wass 1996)

Adverse Results

• Numbers of mute swan and Bewick’s swan showed significant correlations with food sources.

• Swan numbers and their duration of stay were closely associated with the presence of Chara.

• Grazing pressure was low during spring and summer, and Chara colonized the lake in spite of consumption. (Netherlands)

(Noordhuis et al. 2002)

Badzinski et al. 2006.

•Herbivorous waterfowl can reduce quantity of aquatic plants during the breeding or wintering season. •But tundra swan did not have any additional impact on biomass of aquatic plants it at staging areas in fall.

Other Adverse Results

• Lower active in the winter (Squires &Anderson 1997).• Little competition b/w whistling swans and other

waterfowl for food and habitats (Sherwood 1960).• Feeding time did not change in response to a change

in food biomass density (Nolet & Klaassen 2005).• Black swans are apparently highly mobile, and highly

sensitive to quality of their habitat. The net daily population changes became as high as 40-50% on several days in summer. (Mitchell & Wass 1996).

When different herbivores with similar food requirements live within the same ecosystem, the animal may not compete but form a grazing succession, where the feeding activity of one group improved conditions for other species present (Vesey-Fitzgerald 1960, Jarman & Sinclair 1979, Mddock 1979).

Conclusion

• Like rich & comfortable food place.

• Results of swan grazing varies in species, places, and conditions.

• Eutrophication or Good nutrient vector.

• Not always affect reductions of plants.

Destroyer or Succession regulator.

• Not always compete with other animals.

Questions?

http://www.feathersite.com/Poultry/Swans/BRKBkNeck.html http://www.colszoo.org/

animalareas/islands/bswan.html

Black-necked swan

Black swan