Physiological and Environmental Predictors of Black Vulture (Coragyps atratus) Space-use Variation in Recently Expanded Areas

Abstract

Black vultures (Coragyps atratus) are experiencing significant range expansion and population growth in the USA. Black vulture movement ecology has been well studied in their historical range, but few studies have occurred on the leading edge of their expanding range, leaving the drivers of this expansion unclear. Here, we examined the environmental and physiological factors that could influence space-use in vultures at the edge of their range. We used high-resolution movement data from 14 black vultures trapped and tagged in Oklahoma, USA to estimate home range and core area size based on three different methods of estimation: Minimum Convex Polygon, the Dynamic Brownian-bridge Movement Model, and Autocorrelated Kernel Density Estimation. We measured environmental variables within their home ranges, including land cover, road density, and landfill density. We also measured hormone concentrations, plasma testosterone and feather corticosterone, and basic morphology. Black vulture home range size was related to proportion of forest cover, road density, and wing-chord length. We found no relationship between feather corticosterone, plasma testosterone, or sex on space-use in black vultures. Our study demonstrates that black vulture space-use may be constrained by their morphology and shaped in response to specific landscape characteristics. When compared to previous home range studies, our results also suggest that space-use strategies may differ between expanding populations and stable populations found in their historical range, carrying important implications for both conservation and management as the species continues to expand.