Patterns of Consumption and Diet Differentiation for Three Breeding Warbler Species During a Spruce Budworm Outbreak

Abstract

Abstract Diets of three warbler species were analyzed during a spruce budworm outbreak in the boreal forest of northern Ontario. Beetles constituted a large portion of the food items consumed by Cape May (Dendroica tigrina), Bay-breasted (Dendroica castanea), and Tennessee (Vermivora peregrina) warblers early in the breeding season (7–11 June), and caterpillars were the most frequently used food category shortly later (18–24 June). Differences in diet served to differentiate the warbler species in the earlier period when Bay-breasted Warblers consumed more beetles, Tennessee Warblers consumed more caterpillars, and Cape May Warblers consumed more flies than the other species. Only Bay-breasted Warblers' continuing preference for beetles differentiated the warblers' diets in the later period. Food-niche overlaps increased for two of the three warbler species pairs between the two periods in June, but there was no change in the overlap between Bay-breasted and Cape May warbler diets.