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

Abstract

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.