Habitat Selection and Reproductive Success in a Population of Cerulean Warblers in Southeastern Ontario

This study investigates the breeding biology, reproductive success and habitat use of a population of Cerulean Warblers (Dendroica cerulea), a poorly understood, threatened migrant songbird. I established study sites in three areas of mature deciduous forest in the Frontenac Axis region of Ontario: two in unmanaged forest, and the third in an area of selective cutting. Reproductive success was high over the two years of the study, with 20 of 27 pairs (74%) successfully fledging at least one young. Nest failure due to predation was relatively low (14.8%), and there were no known instances of brood parasitism by Brown-headed Cowbirds (Molothrus ater). High rates of success, associated with low rates of predation and brood parasitism, are likely attributable to the large area of contiguous forest in this region, which buffers the pressures of forest "edge effects."