Summary & Purpose
Rapid loss of native shrubs and expansion of invasive annual plants like cheatgrass (Bromus tectorum) have altered North American shrub-steppe systems across extensive areas. Predators, like Aquila chrysaetos (Golden Eagles) that forage on shrub-reliant prey, may abandon historically occupied territories or increase their territory size to cope with degraded habitat. We used a multi-season Bayesian occupancy model that accounted for imperfect detection to investigate the associations between landscape cover, fire history, conspecific neighbor density, and occupancy of 36 A. chrysaetos territories in southwestern Idaho and the Morley Nelson Snake River Birds of Prey National Conservation Area, USA from 1986–2022. The probability of A. chrysaetos occupancy at historically occupied territories decreased 25% from 1986—2022 (0.83-0.58). Once territories became vacant for 5 years, they tended to remain vacant, suggesting that they were no longer suitable for eagles, or that no new eagles were recruiting into the population. Territory occupancy was positively associated with shrub cover (β: 0.90, 95% CrI: 0.12 to 1.71) and negatively (albeit weakly) associated with annual herbaceous cover (β: -0.63, 95% CrI: -1.32 to 0.05). Territories closer to other occupied territories had a lower probability of occupancy than territories with distant neighbors (β: -3.89, 95% CrI: -4.61 to -3.14), likely because eagles compensated for degraded habitat by expanding their territories. Years since the territory last burned had a slightly positive effect on occupancy with high uncertainty and a credible interval that overlapped 0 (β: 0.28, 95% CrI: -0.26 to 0.87). The probability of detecting eagles in an occupied territory was high (0.90) and improved in surveys conducted earlier in the day and later in the breeding season. Shrub conversion to invasive grasslands has negative bottom-up consequences on A. chrysaetos territory occupancy, which may decrease the local carrying capacity for eagles in this area.
Date of Publication or Submission
8-22-2025
DOI
https://doi.org/10.18122/bio_data.14.boisestate
Funding Citation
Financial and logistical support was provided by the Bureau of Land Management, United States Fish and Wildlife Service, and United States Geological Survey. Additional funding was provided by the Hycroft Mining Corporation and the Boise State University Raptor Research Center.
Data Source Credits
Combined Wildland Fire Dataset, Welty and Jeffries, 2022.
Date: February 7, 2022
URL: https://www.usgs.gov/data/combined-wildland-fire-datasets-united-states-and-certain-territories-1800s-present
DOI: 10.5066/P9ZXGFY3
Rangeland Analysis Platform vegetation cover rasters, Allred et al., 2021.
Date: August 1, 2022
URL: http://rangeland.ntsg.umt.edu/data/rap/rap-vegetation-cover/v3/
DOI: http://dx.doi.org/10.1111/2041-210x.13564
Single Dataset or Series?
Series
Data Format
*.csv; *.txt
File Size
461 KB
Data Attributes
See README.txt
Time Period
1986-2022
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Use Restrictions
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Recommended Citation
Santiago, Ashley L.; Cruz, Jennyffer; Delparte, Donna M.; Kochert, Michael N.; Steenhof, Karen; Weldon, Joseph M.; and Heath, Julie A.. (2025). Dataset for Landscape Changes and Declines in Aquila chrysaetos (Golden Eagle) Territory Occupancy in Southwestern Idaho [Data set]. Retrieved from https://doi.org/10.18122/bio_data.14.boisestate