Monitoring abundance of golden eagles in the western United States

Abstract

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.

Environmental cues used by Greater Sage-Grouse to initiate altitudinal migration

“…Survey data Link 2002, 2011;Thogmartin et al 2004;Nielson et al 2008) and data from largescale monitoring efforts like the west-wide golden eagle survey (Millsap et al 2013, Nielson et al 2014). …”

“…This approach reduced the potential bias that could result if larger leks tended to be monitored earlier (e.g., 1965-1980; larger lek = more males) and many smaller leks were only recently included in the monitoring efforts. This hierarchical modeling approach included both fixed and random effects and was similar to approaches used to estimate trends in Breeding Bird Survey data Link 2002, 2011;Thogmartin et al 2004;Nielson et al 2008) and data from large-scale monitoring efforts like the west-wide golden eagle survey (Millsap et al 2013, Nielson et al 2014. A complete description of this modeling approach and assumptions made is included in Appendix II.…”

Modeling Late-Summer Distribution of Golden Eagles (Aquila chrysaetos) in the Western United States

“…A visual mark-recapture procedure was used in the study, but this method [2] was also non-interventive. Potential observer effects (e.g., some better than others) was controlled by yearly pre-survey training, using only experienced golden eagle biologists, rotating observers within the aircraft on a daily basis, and rotating north and south crews.…”

Ecosystem processes, land cover, climate, and human settlement shape dynamic distributions for golden eagle across the western US

“…Golden eagles Aquila chrysaetos are a widely distributed species that occupy vast, rugged landscapes across the northern hemisphere, with annual ranges that can be continental in scale (Kochert et al ., ). In the western United States (US), golden eagle populations currently appear to be stable (Millsap et al ., ; Nielson et al ., ), though there is a growing concern that increased anthropogenic energy development and land‐use change may result in significant population declines. The US, for example, is one of many nations expected to experience increased growth in renewable energy development, of which wind energy will play a prominent role (US Energy Information Administration ).…”