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

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.