BLACK-THROATED BLUE WARBLER AND VEERY ABUNDANCE IN RELATION TO UNDERSTORY COMPOSITION IN NORTHERN MICHIGAN FORESTS

Abstract

Abstract Balsam fir (Abies balsamea) understory may be an important predictor of Black-throated Blue Warbler (Dendroica caerulescens) and Veery (Catharus fuscescens) distributions in northern hardwood forests that are heavily browsed by white-tailed deer (Odocoileus virginianus). We examined the abundance and age ratios of Black-throated Blue Warblers, and the abundance of Veerys, in 16 plots of hardwood forest with different understory composition within a heavily browsed region of the Hiawatha National Forest in Michigan's eastern Upper Peninsula. Four of these 36-ha plots had minimal understory and 12 had dense understory with variable amounts of balsam fir. Black-throated Blue Warbler abundance was significantly greater in plots with an average of 27% balsam fir understory cover than in plots dominated by deciduous understory; no Black-throated Blue Warblers were detected on the minimal understory plots. Age ratios did not differ significantly relative to balsam fir understory density. Veery abundance...