Stable-carbon and hydrogen isotope ratios reveal breeding origins of red-winged blackbirds

We investigated the potential of using stable-carbon (delta(13)C) and hydrogen (delta D) isotope ratios in feathers of Red-winged Blackbirds (Agelaius phoeniceus) to delineate geographic origins where feathers were grown. We used outer primary feathers from territorial male blackbirds along a broad latitudinal transect from Louisiana, USA to Saskatchewan, Canada. Feather delta D values showed an expected depletion with latitude, and were correlated strongly (r(2) = 0.83) with the mean growing season delta D for precipitation at collection sites. Feather delta(13)C values revealed that blackbirds fed on both C-3 and C-4 based foodwebs. Inputs of C-4-based carbon likely related to consumption of agricultural crops such as corn and sorghum. Overall, our dual isotope approach showed great potential as a means of delineating breeding origins of blackbirds throughout the continental Midwest, and supports previous findings that FD measurements of feathers are strongly correlated with precipitation and latitude throughout the central region of the continent.