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A Population Estimate for Golden Eagles in the Western United States
Author(s) -
GOOD RHETT E.,
NIELSON RYAN M.,
SAWYER HALL,
MCDONALD LYMAN L.
Publication year - 2007
Publication title -
the journal of wildlife management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.94
H-Index - 111
eISSN - 1937-2817
pISSN - 0022-541X
DOI - 10.2193/2005-593
Subject(s) - eagle , transect , population , geography , range (aeronautics) , distance sampling , demography , population size , ecology , biology , engineering , aerospace engineering , sociology
ABSTRACT Researchers have suggested golden eagle ( Aquila chrysaetos ) populations may be declining in portions of their range. However, there are few baseline data describing golden eagle populations across their range in the western United States. We used aerial line transect distance methodology with a double‐observer modification to estimate golden eagle population numbers in 4 bird conservation regions of the western United States. We conducted surveys from 16 August to 8 September 2003, after most golden eagles had fledged and before fall migration. The goal of our sampling strategy was to provide >80% power (α = 0.1) to detect an annual rate of total population change >3% per year over a 20‐year period. We observed 172 golden eagles across 148 transects and estimated 27,392 golden eagles (90% CI: 21,352‐35,140) occurred in the study area during the late summer and early fall of 2003. Following the surveys, we used Monte Carlo simulation to determine the statistical power to detect trends in the golden eagle populations if yearly surveys were continued over a 20‐year monitoring period. The simulation indicated the desired power could be achieved under the current methodology and sample size. The methods utilized in this study can be implemented for other raptor species when population estimates that include nonbreeding members of a population are needed. The results of this study can be utilized by professionals to help manage golden eagle populations and to develop conservation strategies.