Spatial variation in foraging of the Black-throated Green Warbler along the shoreline of northern Lake Huron

Robert Smith
Michael Hamas
Matthew Dallman
David Ewert

Abstract

The Great Lakes strongly influence local climate, vegetation, and animal communities, all of which are important to both migrating and breeding birds. This influence can be considerable during springtime in nearshore habitats, as onshore winds depress air temperatures, delaying development of shoreline vegetation relative to inland areas. These developmental differences also may affect abundance, distribution, activity, and growth of insect prey, resulting in spatially-related differences in foraging by birds. Here we test the hypothesis that northern Lake Huron influences the foraging behavior of Black-throated Green Warblers (Dendroica virens) during both migratory periods and the breeding season. We detected spatial variation in a number of variables we used to describe foraging, with most differences occurring during spring migration. We suggest that birds primarily varied foraging in response to spatial differences in prey resulting from microclimatic influences of nearby Lake Huron. We also suggest that emerging aquatic insects in shoreline habitats, primarily midges (Diptera: Chironomidae), are important to birds and propose that this abundant prey source has a primary influence on foraging.