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Golden eagle population trends in the western United States: 1968-2010

Journal of Wildlife Management

By:
, , , , , , and
DOI: 10.1002/jwmg.588

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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 +0.40% per year (95% CI = −0.27% to 1.00%), suggesting a stable population. We also estimated the average rate of population change for the period 1990–2010 was +0.5% per year (95% CI = −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. © 2013 The Wildlife Society.

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Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Golden eagle population trends in the western United States: 1968-2010
Series title:
Journal of Wildlife Management
DOI:
10.1002/jwmg.588
Volume
77
Issue:
7
Year Published:
2013
Language:
English
Publisher:
Wiley
Contributing office(s):
Patuxent Wildlife Research Center
Description:
13 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Wildlife Management
First page:
1436
Last page:
1448
Time Range Start:
1968-01-01
Time Range End:
2010-12-31
Country:
United States
State:
Arizona;California;Colorado;Idaho;Iowa;Kansas;Minnesota;Montana;Nebraska;Nevada;New Mexico;North Dakota;Oklahoma;Oregon;South Dakota;Texas;Utah;Washington;Wyoming
Other Geospatial:
Badlands And Prairies;Chihuahuan Desert;Coastal California;Great Basin;Northern Pacific Rainforest;Northern Rockies;Prairie Potholes;Shortgrass Prairie;Sierra Madre Occidental;Sierra Nevada;Sonoran And Mojave Deserts;Southern Rockies/colorado Plateau