Spatial and temporal patterns in age structure of Golden Eagles wintering in eastern North America

Abstract

The behavior of wildlife varies seasonally, and that variation can have substantial demographic consequences. This is especially true for long‐distance migrants where the use of landscapes varies by season and, sometimes, age cohort. We tested the hypothesis that distributional patterns of Golden Eagles (Aquila chrysaetos) wintering in eastern North America are age‐structured (i.e., birds of similar ages winter together) through the analysis of 370,307 images collected by motion‐sensitive trail cameras set over bait during the winters of 2012–2013 and 2013–2014. At nine sites with sufficient data for analysis, we documented 145 eagle visits in 2012–2013 and 146 in 2013–2014. We found significant between‐year variation in age structure of wintering eastern Golden Eagles, driven largely by annual differences in the proportion of first‐winter birds. However, although many other species show spatial structure in wintering behavior, our analysis revealed no latitudinal organization among age cohorts of wintering eastern Golden Eagles. The lack of age‐related latitudinal segregation in wintering behavior does not exclude the possibility that these eagles have sex‐based or other types of dominance hierarchies that could result in spatial or temporal segregation. Alternatively, other mechanisms such as food availability or habitat structure may determine the distribution and abundance of Golden Eagles in winter.

Where east meets west: Phylogeography of the high Arctic North American brant goose

“…There was an east-west partition in both marker types, although more discrete in mtDNA. This is consistent with migratory routes detected using band recovery and telemetry data (Boyd et al, 2013;Castelli et al, 2010;Erskine, 1988;Leach et al, 2018;Pennycuick et al, 2011). In addition, this genetic partition corresponds with the described phenotypically distinct subspecies in the west (nigricans) and in the east (hrota).…”

The ecology of ageing in wild societies: linking age structure and social behaviour in natural populations

“…This differs to many other demographic characteristics that can be captured in a single statistic, such as population size, growth rate or sex ratio. Typically, animal population age structure is quantified as either the mean or median age of a population [65,[282][283][284], or as the proportion in a given age-cohort, such as prime-aged or juvenile individuals [61,65,93,206,207,266,282,[285][286][287][288][289][290]. While these statistics contain information regarding the central tendency and aspects of skew, we suggest future research should re-establish quantitative definitions of age structure such that maximum information on the distribution of age can be captured, upon which hypotheses can then be tested.…”