Dietary dissimilarity and variation among swallows and flycatchers

Abstract

Aerial insectivores are experiencing population declines in North America, with swallows declining more steeply than flycatchers. Differences in population trends may be explained by differences in prey use. I used DNA metabarcoding of feces to compare the dietary composition and breadth of two flycatchers: Empidonax alnorum (Alder Flycatcher), E. minimus (Least Flycatcher), and four swallows: Hirundo rustica (Barn Swallow), Riparia riparia (Bank Swallow), Tachycineta bicolor (Tree Swallow), and Petrochelidon pyrrhonota (Cliff Swallow). I additionally explored variation in aquatic dietary richness of E. alnorum, H. rustica, and T. bicolor with the amount of water, agriculture, and woody vegetation within their foraging area, along with seasonal and temporal effects. I found significant differences between the diets of all six species. My thesis highlights the significance of aquatic emergent insects as a food source for swallows and flycatchers, and the importance of considering diel effects when studying the diets of generalist insectivores.