Research Article Golden Eagle Population Trends in the Western United States: 1968–2010 BRIAN A. MILLSAP, 1 Division of Migratory Bird Management, U.S. Fish and Wildlife Service, 2105 Osuna NE, Albuquerque, NM 87113, USA GUTHRIE S. ZIMMERMAN, Division of Migratory Bird Management, U.S. Fish and Wildlife Service, 3020 State University Drive East, Modoc Hall, Suite 2007, Sacramento, CA 95819, USA JOHN R. SAUER, U.S. Geological Survey, Patuxent Wildlife Research Center, 12100 Beech Forest Road, Laurel, MD 20708, USA RYAN M. NIELSON, Western EcoSystems Technology, Inc., 415 W. 17th Street, Suite 200, Cheyenne, WY 82001, USA MARK OTTO, Division of Migratory Bird Management, U.S. Fish and Wildlife Service, Patuxent Wildlife Research Center, 11510 American Holly Drive, Laurel, MD 20708, USA EMILY BJERRE, Division of Migratory Bird Management, U.S. Fish and Wildlife Service, Patuxent Wildlife Research Center, 11510 American Holly Drive, Laurel, MD 20708, USA ROBERT MURPHY, Division of Migratory Bird Management, U.S. Fish and Wildlife Service, P.O. Box 1306, Albuquerque, NM 87103, USA ABSTRACT In 2009, the United States Fish and Wildlife Service promulgated permit regulations for the unintentional lethal take (anthropogenic mortality) and disturbance of golden eagles (Aquila chrysaetos). Accurate population trend and size information for golden eagles are needed so agency biologists can make informed decisions when eagle take permits are requested. To address this need with available data, we used a log-linear hierarchical model to average data from a late-summer aerial-line-transect distance-sampling survey (WGES) of golden eagles in the United States portions of Bird Conservation Region (BCR) 9 (Great Basin), BCR 10 (Northern Rockies), BCR 16 (Southern Rockies/Colorado Plateau), and BCR 17 (Badlands and Prairies) from 2006 to 2010 with late-spring, early summer Breeding Bird Survey (BBS) data for the same BCRs and years to estimate summer golden eagle population size and trends in these BCRs. We used the ratio of the density estimates from the WGES to the BBS index to calculate a BCR-specific adjustment factor that scaled the BBS index (i.e., birds per route) to a density estimate. Our results indicated golden eagle populations were generally stable from 2006 to 2010 in the 4 BCRs, with an estimated average rate of population change of 0.41% (95% credible interval [CI]: 4.17% to 3.40%) per year. For the 4 BCRs and years, we estimated annual golden eagle population size to range from 28,220 (95% CI: 23,250–35,110) in 2007 to 26,490 (95% CI: 21,760–32,680) in 2008. We found a general correspondence in trends between WGES and BBS data for these 4 BCRs, which suggested BBS data were providing useful trend information. We used the overall adjustment factor calculated from the 4 BCRs and years to scale BBS golden eagle counts from 1968 to 2005 for the 4 BCRs and for 1968 to 2010 for the 8 other BCRs (without WGES data) to estimate golden eagle population size and trends across the western United States for the period 1968 to 2010. In general, we noted slightly declining trends in southern BCRs and slightly increasing trends in northern BCRs. However, we estimated the average rate of golden eagle population change across all 12 BCRs for the period 1968–2010 as þ0.40% per year (95% CI ¼0.27% to 1.00%), suggesting a stable population. We also estimated the average rate of population change for the period 1990–2010 was þ0.5% per year (95% CI ¼0.33% to 1.3%). Our annual estimates of population size for the most recent decade range from 31,370 (95% CI: 25,450–39,310) in 2004 to 33,460 (95% CI: 27,380–41,710) in 2007. Our results clarify that golden eagles are not declining widely in the western United States. Ó 2013 The Wildlife Society. KEY WORDS Aquila chrysaetos, Breeding Bird Survey, golden eagle, hierarchical model, populations, trend, United States. In 2009, the United States Fish and Wildlife Service (Service) published regulations under the Bald and Golden Eagle Protection Act (16 United States Code 668–668d; hereafter Act) that established conditions under which the Service could permit lethal take and disturbance of bald (Haliaeetus leucocephalus) and golden eagles (Aquila chrys- aetos). The Act delegates to the Secretary of the Interior the ability to permit take of the eagles “necessary for the protection of other interests in any particular locality” after determining the take is “compatible with the preservation of the bald eagle or golden eagle.” The regulations define take to mean pursue, shoot, shoot at, poison, wound, kill, capture, trap, collect, destroy, molest, or disturb. In the 2009 Received: 21 August 2012; Accepted: 3 May 2013 1 E-mail: brian_a_millsap@fws.gov The Journal of Wildlife Management; DOI: 10.1002/jwmg.588 Millsap et al.  Golden Eagle Population Trends 1