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Feeding Habits of Swans


Characteristics of Swans. Anseriforms, Anserinae

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Feeding Habits of Swans

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Feeding habits of swans l.jpg

Feeding Habits of Swans

Daijiro Hata

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


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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.


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N American Swans

Mute swan

Trumpeter swan

Tundra swan


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


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Food Type of Swans

  • 3 types of food

    1) Agricultural plants

    - High carbohydrates

    2) Wetland plants

    - Lower carbohydrates than ag. plants

    - Some high water & high fiber content

    3) Animal matter

    - High protein


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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.)


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Sago pondweed

Eelgrass or Wild celery

Widgeon grass

Muskgrass or Skunkweed

http://aquaplant.tamu.edu


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http://aquaplant.tamu.edu


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Population of Swan

  • Population of swans have increased.

    - Conservation

    - Management for recreation

    hunting, watching

    - Low enforcement


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  • 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)


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USGS Website 2001

Mute swan

(Atlantic Flyway)

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

Noordhuis et al. 2002.

Mute & Bewick’s swan

(Netherlands)


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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.


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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.


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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.


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Mitchell & Wass 1996.


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Grazing

  • 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).

Rees 1990.


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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.


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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.


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

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

Nolet et al. 2006


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  • 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)


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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)


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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)


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  • 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.

Badzinski et al. 2006.


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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).


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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).


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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.


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Questions?

Black-necked swan

Black swan

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

http://www.colszoo.org/animalareas/islands/bswan.html