Stable-Carbon and Nitrogen Isotope Ratios of Songbird Feathers Grown in Two Terrestrial Biomes: Implications for Evaluating Trophic Relationships and Breeding Origins

Abstract

The measurement of stable-carbon ( 13 C/ 12 C) and nitrogen ( 15 N/ 14 N) isotope ratios in bird feathers has potential to reveal important information on trophic position and source of feeding during feather formation. This study investigated how stable-nitrogen (δ 15 N) and carbon (δ 13 C) isotope ratios in feathers of insectivorous songbirds and in their supporting foodwebs differed between boreal forest sites (50 feathers representing 5 species) and upland sites associated with southern prairie agro-wetland complexes in Saskatchewan and Manitoba, Canada (108 feathers representing 12 species). No difference in feather δ 13 C values between these biomes was found, but feathers from boreal forest songbirds were depleted in 15 N compared to feathers from birds in southern agricultural areas. This suggests that general trophic models cannot be constructed based on δ 15 N values of feathers of birds from these different biomes alone unless they are related first to local foodweb isotopic signatures. However, foodweb δ 15 N analysis in each biome indicated that the stable isotope approach could be applied successfully to delineate trophic relationships involving birds. In addition, this technique will be a useful tool for investigating the degree of frugivory or nectarivory in birds.