Daijiro Hata Feeding Habits of Swans

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

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

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 celery Sago pondweed Widgeon grass Muskgrass or Skunkweed

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), (1999). (Conover & Kania 1994, USGS Website 2001) Tundra swan: Pacific Flyway Pop. increased since 1940s, Western 50000(1958), (2005). (Eastern ) (Sherwood 1960, ADFG Website 2005)

Noordhuis et al Mute & Bewick’s swan (Netherlands) USGS Website 2001 Mute swan (Atlantic Flyway) m#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 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 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 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 /day, and loss rates in periods of decline of /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 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.

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