Stable isotope analysis of local avian diets

Abstract

Stable Isotope Analysis (SIA) quantifies the proportion of 13C and 15N within an organism’s tissue and may be used in trophic and nutrient assimilation analysis (Hobson and Sealy 1991). Birds were mist-netted at the North Maple River MAPS site between July 17 and August 1, 2008. Birds were identified and banded according to MAPS protocol and blood samples of 100 μl were taken. Food items were also collected at site and sorted into three groups: berries, aquatic insects, and terrestrial insects. Blood and diet samples were dried and analyzed for δ 13C and δ 15N. Bird isotope signatures were adjusted with discrimination factors and plotted within a mixing model. Proportions for species within model were calculated using IsoSource (interval=1.0, tolerance=0.05). All species, excluding Yellow Warblers, Black-capped Chickadees, and Gray Catbirds, assimilated at least 50% of nutrients from the terrestrial food group. SIA is a new tool for diet analysis and more research is necessary to determine more accurate discrimination factors for North American avifauna.