Stable hydrogen isotopes identify leapfrog migration, degree of connectivity, and summer distribution of Golden Eagles in eastern North America

• Published in: The Condor (Los Angeles, Calif.) Calif.), 2015-08, Vol.117 (3), p.414-429
• Main Authors: Nelson, David M, Braham, Melissa, Miller, Tricia A, Duerr, Adam E, Cooper, Jeff, Lanzone, Michael, Lemaître, Jérôme, Katzner, Todd
• Format: Article
• Language: English
• Subjects: adults; Animal behavior; Animal populations; Aquila chrysaetos; Aviculture; biodiversity; Bird migration; Bird populations; Birds; Birds of prey; breeding season; Breeding seasons; carbon; Carbon isotopes; Connectivity; deuterium; Dispersal; eagles; Feathers; Food webs; Geodetic position; Golden Eagle; Hydrogen isotopes; Isotopes; juveniles; Latitude; migration; migratory behavior; Migratory birds; MIGRATORY CONNECTIVITY; molting; nitrogen; North America; Ornithology; Seasonal migration; stable isotopes; Summer; Telemetry
• ISSN: 0010-5422; 1938-5129; 1938-5129; 2732-4621
• DOI: 10.1650/CONDOR-14-209.1

Knowledge of the distribution and movements of populations of migratory birds is useful for the effective conservation and management of biodiversity. However, such information is often unavailable because of the difficulty of tracking sufficient numbers of individuals. We used more easily obtained feather stable hydrogen isotope ratios (δ2H) to predict the summer grounds of the small, threatened, and migratory population of Golden Eagles (Aquila chrysaetos) in eastern North America. We then identified summer locations and the extent of migratory connectivity for this population. We collected δ2H (δ2Hf), stable carbon isotope (δ13C), and stable nitrogen isotope (δ15N) data from the body feathers of 47 juvenile, subadult, and adult Golden Eagles. Values of δ13C and δ15N suggested that all but 2 birds obtained food from terrestrial-based food webs and therefore that δ2H data were appropriate for inferring the geographic region of molt for the majority of birds. There was relatively large interfeather variation in the δ2H values of subadults vs. adults, suggesting that these groups molted at different times and places. The most negative δ2Hf values from birds with known summering grounds exhibited (1) a negative correlation with their summering latitude, and (2) a positive correlation with amount-weighted δ2H values of May–August precipitation at the summer location. These data validate the use of δ2Hf values for inferring the summer locations of Golden Eagles of unknown origin. Likelihood-of-origin maps derived from δ2Hf values revealed that (1) the majority of birds spent the breeding season in central Québec and Labrador, and (2) birds that wintered at southern latitudes, from approximately northern Alabama to southwestern Virginia, migrated about twice the distance of birds that wintered at northern latitudes, from Pennsylvania to New York. We observed a positive relationship between δ2Hf values and the latitude of the wintering location, which, along with the likelihood-of-origin maps, revealed moderate patterns of leapfrog migration and migratory connectivity.