Foraging behaviour of Tree Swallows over acidified and nonacidic lakes

Abstract

We studied the effects of lake acidification on foraging behaviour of Tree Swallows (Tachycineta bicolor) at the Experimental Lakes Area in northwestern Ontario. Predictions suggest that food quantity and (or) food quality may be important factors related to the reproductive success of birds nesting near acidified bodies of water. Therefore, we investigated the extent to which Tree Swallows (aerial insectivores) use the affected ecosystem as a food resource base. We showed that breeding Tree Swallows foraged on the abundant chironomids emerging at their nest-site lakes before searching for food elsewhere. Chironomid abundance was greatest during the period when Tree Swallows produced their eggs, and declined significantly during periods when Tree Swallows incubated their eggs and fed their nestlings. The data suggest that the reproductive success of Tree Swallows nesting near lakes (and other aerial insectivores that primarily rely on emerging aquatic insects for food) is potentially at risk should changes in the quantity and (or) quality of emerging chironomids result from acidification.