A non-invasive genetic evaluation of population size, natal philopatry, and roosting behavior of non-breeding eastern imperial eagles (Aquila heliaca) in central Asia

Abstract

Roughly one-third of all eagle species are considered to be threatened or endangered, but the ecology of most eagles remains poorly understood. While the pronounced territoriality of breeding adults facilitates behavioral studies, the demography of non-breeding individuals (pre-adults and non-territorial floaters) is almost completely unknown. Traditionally, limited data on pre-adult and floater movement come from wing-tagging and/or telemetry studies. As an alternative to these methods we used genetic analyses of non-invasively collected feathers to investigate the population biology of non-breeding eastern imperial eagles (Aquila heliaca) in Kazakhstan. Microsatellite profiles of shed feathers indicate that eastern imperial eagles roost communally with other raptors. Furthermore, roosts are large and dynamic: 287 non-breeding eastern imperial eagles were detected in our sample, and a mark-recapture analysis estimated the total number to be 308 ± 8. The natal origins of these individuals were investigated by comparing their microsatellite profiles to those available for >90% of the eastern imperial eagle chicks hatched at the study site over the six previous breeding seasons. Only 4% of the individuals genetically matched a chick, suggesting that the reserve may serve as a critical refugium for pre-adults and itinerant floaters. Feathers have long been recognized as a suitable source of DNA, but few studies have used wide-scale, non-invasive collections of feathers (>1,000 samples) to investigate fundamental aspects of avian biology. Our research demonstrates that non-invasive genetic analyses of feathers can be used to evaluate population size, natal philopatry, and local movements of birds that are difficult to study using traditional means.