Anthropogenic subsidies and wildfire influence density, occupancy, and species interactions of three avian predators

Anthropogenic subsidies and disturbance can benefit generalist avian species by providing additional food, nesting, and perching resources. In the sagebrush biome, anthropogenic subsidies have led to increases in the number of common ravens (Corvus corax; hereafter ravens), red-tailed hawks (Buteo jamaicensis), and Swainson's hawks (Buteo swainsoni), but it is unclear how wildfire disturbance may be affecting these species. We used 6 years of count data (2017–2022) to investigate the effects of anthropogenic subsidies and wildfire on density, occupancy, interspecific density dependence, and interactions of these three sympatric predators in five study areas in eastern Oregon. Estimated mean relative densities for all species varied annually, ranging from 1.00 to 2.05 km⁻² for ravens, from 0.46 to 1.09 km⁻² for red-tailed hawks, and from 0.07 to 0.38 km⁻² for Swainson's hawks. Mean occupancy probability was 0.78 across all study areas for red-tailed hawks and varied by study area for ravens and Swainson's hawks, ranging from 0.62 to 0.94 and from 0.70 to 0.97, respectively. N-mixture and occupancy models indicated that anthropogenic subsidies and recent wildfires (≤10 years) were positively associated with the density and occupancy of ravens and red-tailed hawks. However, only road density was associated with the occupancy of Swainson's hawks. There were no interspecific density-dependent effects for ravens and red-tailed hawks, but Swainson's hawk density decreased as densities of ravens and red-tailed hawks increased. Multispecies occupancy models indicated that most occupancy probabilities associated with anthropogenic subsidies were independent of allospecific presence. However, occupancy probabilities were influenced by wildfire, indicating negative interactions between Swainson's hawks and ravens but positive interactions between Swainson's and red-tailed hawks. Our results provide evidence that anthropogenic subsidies create hotspots of generalist predators in sagebrush ecosystems fragmented by wildfire. These increased densities may lead to human–wildlife conflicts, displacement of specialist predator species, and greater risk of predation to prey species of conservation concern.