Breeding Ecology of Golden Eagles in Western Washington
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Raptors breeding in novel environments must find sufficient food resources to survive and reproduce. Available prey and landscapes surrounding territories can influence aspects of parental care and reproductive output. I investigated the influence of prey size and landscape on parental care and territory occupancy, respectively, in western Washington, where as many as 86 Golden Eagle (Aquila chrysaetos) territories have been described. Much of the region is dominated by closed-canopy forests and lacks the typical prey communities commonly associated with Golden Eagle diets in North America. I provide support for the prey size hypothesis in a study of Golden Eagles utilizing a novel prey species. I utilized direct observation of occupied nests in the Cascade Mountains of Washington, U.S.A to record prey use and parental care. Over 70% of prey items delivered to nests were mountain beaver (Aplodontia rufa), and nearly 88% of prey deliveries were made by the male parent. Relative prey mass was among the largest reported in similar studies of prey use and parental care. Consequently, female confinement was longer than reported in other studies of Golden Eagle parental care and approximately equal to what was predicted by the prey size hypothesis. Greater asymmetry in patterns of parental care may select for further reversed size dimorphism in raptors. I also investigated the effects of land cover, topography, and land use on occupancy of Golden Eagle territories (n = 19) using historic survey records and remotely-sensed aspects of the landscape. I found that territory occupancy is positively associated with elevation and elevation range, and negatively associated with forest cover. That is, a breeding territory was more likely to be frequently occupied if it occurred at a higher elevation, included a larger range of elevations, or included less forest cover. Forest management including timber harvest is likely providing suitable foraging habitat for Golden Eagles breeding in the region.
- Forestry