Homeward bound: annual breeding home range size and overlap in Broad-winged Hawks ( Buteo platypterus ) and the effects of sex, productivity, and ecoregion

Abstract

Documenting home range size, and identifying the variables influencing it, is key to understanding raptor population ecology and to addressing conservation issues. The Broad-winged Hawk (Buteo platypterus, hereafter broadwing) is a small forest buteo that travels over 8,000 km between its breeding range in North America and wintering range in Central and South America. Although conspicuous during migration, its secretive behavior while nesting hinders data collection on behavior and movements during the breeding season. We calculated breeding home ranges of 14 telemetry-tracked broadwings in northeastern USA and analyzed the effects of intrinsic (sex and nest productivity) and extrinsic (ecoregion) variables, using autocorrelated kernel density estimations. Breeding home ranges were 20 times larger in males than in females, in line with the strong division of labor between sexes observed in raptors. Breeding home ranges were larger in the most southerly ecoregion, suggesting that adults may need to move more to find prey for their nestlings or the habitat is less suitable in this ecoregion. We found no effect of nest productivity, although sample size was small. We assessed nest site fidelity and home range overlap across years for five adults. We found annual breeding home ranges overlapped (>0.85 in all cases) and inter-annual nest distances were less than 200 m on average, indicating a strong fidelity to the breeding home range and to the nest site area. To our knowledge, this is the first study using telemetry data to calculate breeding home ranges of this secretive forest raptor. Our findings indicate that broadwing breeding home ranges and nesting locations may remain stable over several years. Understanding and protecting the habitats used by nesting broadwings throughout their breeding range could be important to their long-term conservation.