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Distribution and Abundance of Aquila chrysaetos (Golden Eagles) in the East Contra Costa County Habitat Conservation Plan/Natural Community Conservation Plan Area, California

Open-File Report 2020-1107
Prepared in cooperation with East Contra Costa County Habitat Conservancy Science and Research Grant Program, East Bay Regional Parks District, Save Mount Diablo’s Mary Bowerman Science and Research Grant Program, and NextEra Energy
By: , , and 
https://doi.org/10.3133/ofr20201107

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Abstract

The East Contra Costa County Habitat Conservation Plan/Natural Community Conservation Plan (HCP/NCCP) Preserve System was designed to protect and enhance ecological diversity and function in eastern Contra Costa County, California. Aquila chrysaetos (golden eagle) is a special-status species expected to benefit from biological goals of the HCP/NCCP. As part of a broader study, we estimated site-occupancy, abundance, and reproduction of golden eagles in the HCP/NCCP inventory area in 2019. We completed 99 surveys and recorded a total of 50 detections of territorial pairs of eagles at 20 (67 percent) of 30 sites (13.9-square-kilometer [km2] plots). Detection probability of territorial pairs was highest in January and February (≥0.75) and lowest in mid-June to late July (<0.50). After correcting for imperfect detection, the expected probability of site-occupancy was 0.69 (standard error [SE] = 0.09), and mean expected abundance was 0.76 pairs per site (SE = 0.16), or 27.4 pairs per 500 km2. We found evidence of successful nesting (≥1 young fledged) for 3 (14 percent) of 22 pairs of eagles monitored in 2019. Our study design and baseline results should be useful for future monitoring and conservation of golden eagles in the HCP/NCCP area.

Suggested Citation

Wiens, J.D., Kolar, P.S., and Bell, D.A., 2020, Distribution and abundance of Aquila chrysaetos (golden eagles) in East Contra Costa County Habitat Conservation Plan/Natural Community Conservation Plan area, California: U.S. Geological Survey Open-File Report 2020-1107, 11 p., https://doi.org/10.3133/ofr20201107.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Study Area
  • Methods
  • Results
  • Discussion
  • Acknowledgments
  • References Cited
  • Appendix 1. Ranking of Candidate Occupancy and Abundance Models
Publication type Report
Publication Subtype USGS Numbered Series
Title Distribution and abundance of Aquila chrysaetos (golden eagles) in East Contra Costa County Habitat Conservation Plan/Natural Community Conservation Plan area, California
Series title Open-File Report
Series number 2020-1107
DOI 10.3133/ofr20201107
Publication Date September 16, 2020
Year Published 2020
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Forest and Rangeland Ecosystem Science Center
Description iv, 11 p.
Country United States
State California
County Contra Costa County
Online Only (Y/N) Y
Additional publication details