Landscape changes and declines in Aquila chrysaetos (Golden Eagle) territory occupancy in southwestern Idaho. Santiago, A. L, Cruz, J., Delparte, D. M, Kochert, M. N, Steenhof, K., Weldon, J. M, & Heath, J. A Ornithological Applications, September, 2025. ![Landscape changes and declines in Aquila chrysaetos (Golden Eagle) territory occupancy in southwestern Idaho [link]](https://bibbase.org/img/filetypes/link.svg "link")
Paper doi abstract bibtex 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 Eagle) that forage on shrub-reliant prey, may abandon historically occupied territories or increase their territory size to cope with degraded habitat. We used a multiseason 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 to 2022. The probability of A. chrysaetos occupancy at historically occupied territories decreased 25% from 1986 to 2022 (0.83–0.58). Once territories became vacant for 5 yr, 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territory occupancy, which may decrease the local carrying capacity for eagles in this area.Native shrub habitat has been replaced by non-native annual grasses across wide areas in the Western U.S.We built an occupancy model to assess the effects of landscape cover on the temporal variation in Aquila chrysaetos (Golden Eagle) territory occupancyThe probability of A. chrysaetos territory occupancy decreased from 1986 to 2022Increased annual herbaceous cover and a higher density of occupied A. chrysaetos territories affected the probability of occupancy negativelyShrub cover and less frequent fires increased the probability of occupancyLandscape changes can have bottom-up effects on predators and lead to a lower carrying capacity for eagles in local areas.
@article{santiago_landscape_2025,
title = {Landscape changes and declines in {Aquila} chrysaetos ({Golden} {Eagle}) territory occupancy in southwestern {Idaho}},
issn = {0010-5422},
url = {https://doi.org/10.1093/ornithapp/duaf054},
doi = {10.1093/ornithapp/duaf054},
abstract = {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 Eagle) that forage on shrub-reliant prey, may abandon historically occupied territories or increase their territory size to cope with degraded habitat. We used a multiseason 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 to 2022. The probability of A. chrysaetos occupancy at historically occupied territories decreased 25\% from 1986 to 2022 (0.83–0.58). Once territories became vacant for 5 yr, 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.Native shrub habitat has been replaced by non-native annual grasses across wide areas in the Western U.S.We built an occupancy model to assess the effects of landscape cover on the temporal variation in Aquila chrysaetos (Golden Eagle) territory occupancyThe probability of A. chrysaetos territory occupancy decreased from 1986 to 2022Increased annual herbaceous cover and a higher density of occupied A. chrysaetos territories affected the probability of occupancy negativelyShrub cover and less frequent fires increased the probability of occupancyLandscape changes can have bottom-up effects on predators and lead to a lower carrying capacity for eagles in local areas.},
urldate = {2026-01-21},
journal = {Ornithological Applications},
author = {Santiago, Ashley L and Cruz, Jennyffer and Delparte, Donna M and Kochert, Michael N and Steenhof, Karen and Weldon, Joseph M and Heath, Julie A},
month = sep,
year = {2025},
keywords = {Political Boundaries},
pages = {duaf054},
}
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We used a multiseason 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 to 2022. The probability of A. chrysaetos occupancy at historically occupied territories decreased 25% from 1986 to 2022 (0.83–0.58). Once territories became vacant for 5 yr, 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.Native shrub habitat has been replaced by non-native annual grasses across wide areas in the Western U.S.We built an occupancy model to assess the effects of landscape cover on the temporal variation in Aquila chrysaetos (Golden Eagle) territory occupancyThe probability of A. chrysaetos territory occupancy decreased from 1986 to 2022Increased annual herbaceous cover and a higher density of occupied A. chrysaetos territories affected the probability of occupancy negativelyShrub cover and less frequent fires increased the probability of occupancyLandscape changes can have bottom-up effects on predators and lead to a lower carrying capacity for eagles in local areas.","urldate":"2026-01-21","journal":"Ornithological Applications","author":[{"propositions":[],"lastnames":["Santiago"],"firstnames":["Ashley","L"],"suffixes":[]},{"propositions":[],"lastnames":["Cruz"],"firstnames":["Jennyffer"],"suffixes":[]},{"propositions":[],"lastnames":["Delparte"],"firstnames":["Donna","M"],"suffixes":[]},{"propositions":[],"lastnames":["Kochert"],"firstnames":["Michael","N"],"suffixes":[]},{"propositions":[],"lastnames":["Steenhof"],"firstnames":["Karen"],"suffixes":[]},{"propositions":[],"lastnames":["Weldon"],"firstnames":["Joseph","M"],"suffixes":[]},{"propositions":[],"lastnames":["Heath"],"firstnames":["Julie","A"],"suffixes":[]}],"month":"September","year":"2025","keywords":"Political Boundaries","pages":"duaf054","bibtex":"@article{santiago_landscape_2025,\n\ttitle = {Landscape changes and declines in {Aquila} chrysaetos ({Golden} {Eagle}) territory occupancy in southwestern {Idaho}},\n\tissn = {0010-5422},\n\turl = {https://doi.org/10.1093/ornithapp/duaf054},\n\tdoi = {10.1093/ornithapp/duaf054},\n\tabstract = {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 Eagle) that forage on shrub-reliant prey, may abandon historically occupied territories or increase their territory size to cope with degraded habitat. We used a multiseason 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 to 2022. The probability of A. chrysaetos occupancy at historically occupied territories decreased 25\\% from 1986 to 2022 (0.83–0.58). Once territories became vacant for 5 yr, 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. 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