Spatial and Temporal Patterns in Age Structure of Golden Eagles (Aquila chrysaetos) Wintering in Eastern North America

Kenney, Macy
Behavior of wild animals varies seasonally, especially for migratory species that may spend sequential seasons in very different habitats. However, in the case of migratory birds, our understanding of behavior tends to derive from studies on breeding grounds. We tested the hypothesis that golden eagles (Aquila chrysaetos) in eastern North America show age-specific wintering behavior by evaluating spatial and temporal patterns in age structure on wintering grounds. We used motion-sensitive trail cameras set at scavenging bait sites over multiple years to collect images of golden eagles in the Appalachians during winters 2013 and 2014. All eagles were aged and age ratios estimated for each year with two different techniques. We tested our estimates of age ratios against a stable age distribution and used the aging technique that produced the most plausible age ratios in subsequent analysis. Age ratios of eagles were not the same at each site (i.e., they varied spatially within a given year) but spatial patterns in age ratios were not consistent across years (i.e., they varied temporally). Site-specific variation in age ratios across years suggests that eagles do not show age specific wintering behavior but instead show inter-annual fidelity to wintering sites. Such patterns are inconsistent with previously described age-specific wintering behavior for eagles but consistent with telemetry data from eagles that also show site fidelity by wintering birds.
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