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Open-File Report 2015-1039

Estimation of Occupancy, Breeding Success, and Abundance of Golden Eagles (Aquila chrysaetos) in the Diablo Range, California, 2014

By J. David Wiens, Patrick S. Kolar, Mark R. Fuller, W. Grainger Hunt, and Teresa Hunt

Thumbnail of and link to report PDF (1.9 MB)Abstract

We used a multistate occupancy sampling design to estimate occupancy, breeding success, and abundance of territorial pairs of golden eagles (Aquila chrysaetos) in the Diablo Range, California, in 2014. This method uses the spatial pattern of detections and non-detections over repeated visits to survey sites to estimate probabilities of occupancy and successful reproduction while accounting for imperfect detection of golden eagles and their young during surveys. The estimated probability of detecting territorial pairs of golden eagles and their young was less than 1 and varied with time of the breeding season, as did the probability of correctly classifying a pair’s breeding status. Imperfect detection and breeding classification led to a sizeable difference between the uncorrected, naïve estimate of the proportion of occupied sites where successful reproduction was observed (0.20) and the model-based estimate (0.30). The analysis further indicated a relatively high overall probability of landscape occupancy by pairs of golden eagles (0.67, standard error = 0.06), but that areas with the greatest occupancy and reproductive potential were patchily distributed. We documented a total of 138 territorial pairs of golden eagles during surveys completed in the 2014 breeding season, which represented about one-half of the 280 pairs we estimated to occur in the broader 5,169-square kilometer region sampled. The study results emphasize the importance of accounting for imperfect detection and spatial heterogeneity in studies of site occupancy, breeding success, and abundance of golden eagles.

First posted March 3, 2015

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Suggested citation:

Wiens, J.D., Kolar, P.S., Fuller, M.R., Hunt, W.G., and Hunt, Teresa , 2015, Estimation of occupancy, breeding success, and predicted abundance of golden eagles (Aquila chrysaetos) in the Diablo Range, California, 2014: U.S. Geological Survey Open-File Report 2015-1039, 23 p., https://dx.doi.org/10.3133/ofr20151039.

ISSN 2331-1258 (online)



Contents

Abstract

Introduction

Study Area

Methods

Results

Discussion

Acknowledgments

References Cited

Appendix A. A priori Models Used to Characterize Variation in Detection, Occupancy, and Successful Reproduction of Golden Eagles in the Diablo Range, California, 2014

Appendix B. Multistate Occupancy Detection Histories of 133 Sample Sites Searched Repeatedly for Evidence of Occupancy and Successful Reproduction by Territorial Pairs of Golden Eagles in the Diablo Range, California, 2014


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