Extreme drought increased home range sizes and space use of Aquila chrysaetos (Golden Eagles) in coastal southern California
Data files
Jul 16, 2025 version files 54.04 KB
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README.md
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thomsen_etal_06242025_GOEAdrought_homerangesizes.csv
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Abstract
Aquila chrysaetos (Golden Eagles) are long-lived top predators, vulnerable to a variety of threats. There is increasing concern about the declining population in coastal southern California, which has largely coincided with habitat loss due to urbanization of the region. This Mediterranean-type ecosystem is also experiencing more prolonged and intense droughts, which can reduce the abundance of key prey species, such as jackrabbits (Lepus californicus) and ground squirrels (Otospermophilus beecheyi). However, the impact of drought on Golden Eagles is poorly understood. Here, we used high-resolution GPS tracking data to calculate eagle home ranges and hypothesized that home range size would be influenced by drought such that home ranges would be larger to meet their resource needs with worsening drought severity. Fifty individuals were captured over seven breeding seasons, spanning the time both during and after a historic drought. We also compared space use for different stages of the breeding season throughout each year. Golden Eagle home ranges increased by 77% during extreme drought compared to wetter conditions. Drought-breaking rainfall corresponded with much smaller home ranges compared to home range sizes during drought years. As drought is projected to be more prolonged and frequent in this region with climate change, this may result in increasingly large home range sizes at the same time as eagles are facing ongoing habitat loss and fragmentation from various land use changes. Our results suggest that the frequent and severe drought that is projected for this region could lead to lowered nesting density and increase the risk of further population decline.
Dataset DOI: 10.5061/dryad.h9w0vt4vm
Description of the data and file structure
Seasonal home range sizes of Golden Eagles in southern California 2014-2022
Files and variables
File: thomsen_etal_06242025_GOEAdrought_homerangesizes.csv
Description:
Variables
- eagleID: individual eagle ID
- sex: sex of eagle
- age: age category ("adult" or "subadult")
- season: "winter" (Nov-Jan) "spring" (Feb-Apr) "summer" (May-Jul) "fall" (Aug-Oct)
- nestyear: breeding season year that begins the previous winter in Nov and ends in Oct; calendar year during spring season is used to label the nestyear
- ldistmove: category for individuals that remained in the local study area ("local") versus those that moved beyond outside of the local study area ("ldist") during that season
- floater: category for adults with territories "territory" or floaters "floater"
- PDSI: Palmer Drought Severity Index (PDSI) in February for the South Coast climate division in California for the month of February during the nestyear
- locoh95: home range area as determined by the adaptive local convex hull method (a-LoCoH)
- locoh50: 50% core area as determined by the adaptive local convex hull method (a-LoCoH)
- mcp95.sqkm: home range area as determined by the 95% minimum convex polygon (MCP)
- mcp50.sqkm: core area as determined by the 50% minimum convex polygon (MCP)
- akde.sqkm: home range area as determined by autocorrelated kernel density estimates (AKDE)
- akde50.sqkm: 50% core area as determined by autocorrelated kernel density estimates (AKDE)
- locations: total number of GPS locations per season used in the calculation of home range sizes
