A Survey of Golden Eagles (Aquila chrysaetos) in the Western US: 2011 Annual Report

Western EcoSystems Technology, Inc. (Laramie WY); Nielson, Ryan; Rintz, Troy; McManus, Lindsay; Mcdonald, Lyman

A report for the U.S. Fish & Wildlife Service that provides region-wide transect survey data for Golden Eagles in the Western USA during 2011. We flew aerial line transect surveys using mark-recapture procedures to estimate the number of Golden Eagles (Aquila chrysaetos) in three Bird Conservations Regions (BCRs) in the western U.S. between August 15 and September 15, 2011. The study area consisted of BCRs 9 (Great Basin), 10 (Northern Rockies), and 16 (Southern Rockies / Colorado Plateau). Past surveys (2003 and 2006 – 2010) have included BCR 17 (Badlands and Prairies), but this region was not surveyed in 2011. Instead, extra effort was extended in BCR 16 in an attempt to understand how increased survey effort might improve precision of abundance estimates. This evaluation of increased survey effort in BCR 16 is presented in the Appendix. The summary statistics and analyses presented in this report do not include the additional transects surveyed in BCR 16 in 2011 – only data from the original sample of transects for 2006 – 2011 are presented here. In 2011, we flew 178 transects totaling 14,285 km. We observed 117 Golden Eagle groups within 1000 m of 71 transects for a total of 135 individuals: 14 juveniles, 22 sub-adults, 64 adults, 0 unknown immature (not adults), 33 unknown adults (not juveniles), and 2 of unknown age class. We estimated that a total of 6,199 Golden Eagles (90% confidence interval: 4,732 to 8,555) were within BCR 9 during the survey, a total of 6,862 (90% confidence interval: 4,853 to 9,994) were within BCR 10, and a total of 2,917 (90% confidence interval: 2,053 to 4,228) were within BCR 16. These estimates do not include Golden Eagles that were occupying military lands, elevations above 10,000 ft, large water bodies, or large urban areas. A trend analysis on the number of Golden Eagles observed along each transect 2006 to 2011 found no significant trends (i.e., 90% credible intervals contained zero) in total numbers (all age classes) of Golden Eagles observed in individual Bird Conservation Regions or across the study area during 2006 – 2011. However, the trend analysis indicated there have been statistically significant declines in the total number of Golden Eagles classified as juveniles during the survey in the Southern Rockies / Colorado Plateau (16), and the Badlands and Prairies (17) since 2006.