Trumpeter Swans in the Strawberry Lakes Area of Southeast Saskatchewan

Trumpeter Swans in the Strawberry Lakes Area of Southeast Saskatchewan

Response of wild Trumpeter Swan (Cygnus buccinator) broods to wetland drawdown and changes in food abundance

A brief period of drawdown can stimulate wetland productivity and enhance the attractiveness of a site for breeding Trumpeter Swans (Cygnus buccinator) by providing a nutrient pulse. Drawdown of a pond in Aurora, Ontario, lasting about 8 weeks in late summer and fall 2009 followed by re-flooding increased the abundance of invertebrates, especially snails, in the following year. This response was ephemeral, lasting 1 year. Wild Trumpeter Swans and their cygnets responded by selective feeding the year after drawdown, despite the risk of predation by Snapping Turtles (Chelydra serpentina). There was a strong correlation between the feeding activity of two cygnets and the local abundance of snails in the pond in 2010. The nutritional content, especially protein, calcium, phosphorus, and magnesium, of a variety of abundant foods satisfied the requirements for skeletal growth and development and was higher than that of available commercial duck grower rations. The responsive feeding behaviours of the cygnets are typical of specific appetitive behaviour and suggest that swans rapidly exploit unpredictable nutrient fluxes in their local environment.

Body Size Mediated Coexistence in Swans

Differences in body sizes may create a trade-off between foraging efficiency (foraging gains/costs) and access to resources. Such a trade-off provides a potential mechanism for ecologically similar species to coexist on one resource. We explored this hypothesis for tundra (Cygnus columbianus) and trumpeter swans (Cygnus buccinator), a federally protected species, feeding solely on sago pondweed (Stuckenia pectinata) tubers during fall staging and wintering in northern Utah. Foraging efficiency was higher for tundra swans because this species experienced lower foraging and metabolic costs relative to foraging gains; however, trumpeter swans (a) had longer necks and therefore had access to exclusive resources buried deep in wetland sediments and (b) were more aggressive and could therefore displace tundra swans from lucrative foraging locations. We conclude that body size differentiation is an important feature of coexistence among ecologically similar species feeding on one resource. In situations where resources are limiting and competition for resources is strong, conservation managers will need to consider the trade-off between foraging efficiency and access to resources to ensure ecologically similar species can coexist on a shared resource.

Trumpeter Swan (Cygnus buccinator) behaviour, interactions with Snapping Turtles (Chelydra serpentina), and their Pleistocene history

Snapping Turtles (Chelydra serpentina) prey on and injure Trumpeter Swan (Cygnus buccinator) cygnets. Adult Trumpeter Swans stamp on and attack turtles, and this sometimes saves the lives of cygnets. Stamping behaviour, duetting, clamouring, and mobbing are directed at predators. The stamping behaviour may be derived from the water treading display. During the Pleistocene ice sheet maxima, all Trumpeter Swans east of the Rockies nested within the range of the Snapping Turtle. Snapping Turtle predation may have selected for the stamping behaviour.