Monitoring Abundance of Golden Eagles in the Western United States

Under the Bald and Golden Eagle Protection Act, the United States Fish and Wildlife Service (Service) can authorize take of golden eagles (Aquila chrysaetos), such as nest removal, disturbance, and lethal take, if the take is compatible with the preservation of the golden eagle. The Service needs baseline information on the current abundance and trend of subpopulations of the golden eagle to properly manage take of the species. Annually during late summer of 2006-2012, we used distance sampling on approximately 17,500 km of aerial line transects to estimate golden eagle abundance in 4 Bird Conservation Regions (BCRs; North American Bird Conservation Initiative Monitoring Subcommitte 2007) that collectively cover about 80% of the species' range in the coterminous western United States. We estimated study area abundances of 24,509 (90% CI: 19,406-31,947) in 2006 and 21,715 (90% CI: 18,165-27,624) in 2012, including all breeding and non-breeding individuals. We used a Bayesian hierarchical model to estimate trends in individual BCRs and the entire study area based on numbers of golden eagles counted along surveyed transects. We detected declines (90% credible intervals [CRIs] for trend coefficients <0.0) in numbers of golden eagles classified as juveniles in BCR 10 (Northern Rockies) and BCR 16 (Southern Rockies and Colorado Plateau) during 2006-2012. However, our results indicate the total abundance of golden eagles has not declined 2006-2012 in much of the western United States. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.