The golden eagle has been studied in Washington since the 1970s, when researchers investigated the distribution and diets of the species along the Columbia River. Though the species has never bred in abundance in Washington compared to other western states, concerns about itsí status resulted in a designation as a Candidate species for listing. Potential causes of golden eagle declines in Washington relate to changes in habitat quality during the past several years, including the presence of environmental lead and effects of reduced prey on nest occupancy and success. Necropsies performed on golden eagles at Washington State University between 1980 and into the 1990s indicated high levels of lead contamination in tissue samples (E. Stauber, unpubl. data). Acute and chronic blood toxicosis has been well studied in other large avian predators in recent years, particularly the California Condor (Gymnogyps californianus), where population effects from lead mortality have been significant. Lead toxicosis results in impaired body functions and ultimately death. Spent ammunition consumed by foraging eagles has been identified as a source of lead contamination in condors and eagles worldwide. However, sources of lead contamination in golden eagles in Washington are unknown.
Declines in prey from habitat changes may also be contributing to reductions in the golden eagle population in Washington. Jackrabbits, for example, were once common throughout shrub-steppe habitat in Washington, but have vanished from all but a few areas. In preparation for a state status review of golden eagles, we initiated this baseline study of nesting golden eagles to: 1) determine blood levels of lead; and 2) determine residency status and range size of breeding eagles. We initiated capture, blood analysis, and satellite tracking of golden eagles in 2004.
- To date, of 14 eagles tested for lead, six (43%) had background levels of lead, four (29%) had excessive levels of lead, and four (29%) had levels suggestive of toxicosis.
- There was no consistent geographic pattern associated with lead levels. Sampling has included birds on 20-30% of territories that are typically occupied in Washington, documenting lead contamination as a widespread and important concern for nesting golden eagles.
- Most breeding eagles were resident year-round, and occupied home ranges that averaged 50.6 ± 28.2 km 2 (95% kernels).
- We initiated a diet study of breeding eagles in 2008 to compare golden eagle food habits with those assessed by data collected by researchers 30 years ago. In addition, we are experimenting with cameras as a tool to record feeding behavior.
Watson, J.W., and R.W. Davies. 2005. Range use and contaminants of golden eagles in Washington. Progress Report 1. Washington Department of Fish and Wildlife, Olympia, Washington.
Watson, J.W., and R.W. Davies. 2006. Range use and contaminants of golden eagles in Washington. Progress Report 2. Washington Department of Fish and Wildlife, Olympia, Washington.
- Range use and contaminants of golden eagles in Washington. Progress Report 3