Diet Composition and Mercury Exposure in Bank Swallows (Riparia riparia) Breeding at Lakeshore and Aggregate Pits

Bank Swallows (Riparia riparia), a threatened species in Ontario, breed primarily in banks at lakeshores and in artificial aggregate pits. Inland pits may be ecological traps for this species, but the relative tradeoffs between these two nesting habitats are unknown. Availability of aquatic emergent insects at lakeshores may have associated nutritional benefits (e.g. Omega-3 fatty acids) and contaminants (e.g. mercury) that can directly influence juvenile growth. This study compares these breeding habitats to evaluate dietary differences as revealed by fatty acids, stable isotopes (δ13C, δ15N, δ2H), fecal DNA barcoding, and mercury. Lakeshore-nesting birds had a more aquatic emergent diet than inland birds, foraging on chironomids. Lakeshore juveniles were in better body condition than inland juveniles possibly due to a diet higher in Omega-3 fatty acids. This information is important for management decisions related to the use of inland aggregate pits by this species and conservation of suitable lakeshore nesting habitat