SPATIAL VARIATION IN FORAGING OF THE BLACK-THROATED GREEN WARBLER ALONG THE SHORELINE OF NORTHERN LAKE HURON

The Great Lakes strongly influence local climate, vegetation, and anim al communities, all of which are important to both migrating and breed ing birds. This influence can be considerable during springtime in nea rshore habitats, as onshore winds depress air temperatures, delaying d evelopment of shoreline vegetation relative to inland areas. These dev elopmental differences also may affect abundance, distribution, activi ty, and growth of insect prey, resulting in spatially-related differen ces in foraging by birds. Here we test the hypothesis that northern La ke Huron influences the foraging behavior of Black-throated Green Warb lers (Dendroica virens) during both migratory periods and the breeding season. We detected spatial variation in a number of variables we use d 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 influence s of nearby Lake Huron. We also suggest that emerging aquatic insects in shoreline habitats, primarily midges (Diptera: Chironomidae), are i mportant to birds and propose that this abundant prey source has a pri mary influence on foraging.