Spatial Ecology of Apex Raptors

Abstract

Apex raptors -- large eagles and vultures occupying the highest trophic levels in terrestrial food webs -- require vast home ranges, show high fidelity to nesting territories across decades, and are disproportionately sensitive to landscape-scale habitat fragmentation, direct persecution, and secondary poisoning that collectively drive their populations below viable thresholds across much of Europe. This study characterised the spatial ecology, habitat selection, and landscape connectivity requirements of four European apex raptor species -- bearded vulture (Gypaetus barbatus), golden eagle (Aquila chrysaetos), short-toed eagle (Circaetus gallicus), and white-tailed eagle (Haliaeetus albicilla) -- using GPS-GSM telemetry of 124 individuals across Switzerland, Austria, and the Carpathian Mountains (2018-2022; mean tracking duration 28 +- 6 months; mean 8.4 +- 2.2 fixes/day). Annual home range areas were estimated by kernel density estimation (KDE 95% isopleth). Habitat selection was characterised by resource selection functions (RSFs) fitted by conditional logistic regression at 100 m resolution. Landscape connectivity between breeding territories was modelled using Circuitscape 4.0. Annual home ranges varied from 124 +- 48 km2 (G. barbatus; alpine) to 1,842 +- 412 km2 (H. albicilla; lowland). RSFs identified open habitat with high topographic heterogeneity (G. barbatus), mature deciduous forest edges (A. chrysaetos), open scrubland and wetland margins (C. gallicus), and large water bodies with fish-rich shores (H. albicilla) as the primary landscape determinants of space use. Circuitscape analysis identified 14 pinch-point corridors essential for connectivity among the 284 monitored breeding territories, with 8 corridors crossing major infrastructure barriers (highways, railways). These 14 corridors represent the highest-priority sites for targeted habitat management and wildlife crossing installation under the EU Biodiversity Strategy 2030 species recovery planning