Daijiro Hata

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Feeding Habits of Swans
http//www.flickr.com/photos/singingfish/259448032
/

• Daijiro Hata

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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 lt200 (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.ht
mBackground
Noordhuis et al. 2002. Mute Bewicks 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 sayTundra 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 lt50cm
extensive grazing on SAV)
Bewicks swan max depth is 0.89m, but prefer
shallower water like lt0.45m.
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 Bewicks 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.h
tml