Spatial ecology of winting accipiter hawks: Home range, habitat use, and the influence of bird feeders

Abstract

Despite their likely ecological importance, the basic biology of Cooper's (Accipiter cooperii) and Sharp-shinned (A. striatus) Hawks remains poorly understood. This is particularly true during the winter, when even basic information on the spatial ecology of these species is largely unknown. Thus, we characterized the home range size and habitat chosen by these species as part of a larger study on wintering Accipiter hawks. We also compared our findings of bird feeder use by Cooper's Hawks to our previously published study on Sharp-shinned Hawks. During the winters of 1999-2004, we intensively radio-tracked 21 Sharp-shinned Hawks and six Cooper's Hawks in rural areas, and eight Cooper's Hawks in urban areas. We found that Sharp-shinned Hawks and Cooper's Hawks in rural areas used significantly larger areas than did Cooper's Hawks in urban areas, and that adult hawks generally used smaller areas than immature individuals. Habitat use by Cooper's Hawks and Sharp-shinned Hawks in rural areas was nearly identical and focused mostly on forested and grass habitat types. Cooper's Hawks in urban areas focused disproportionately on grassy areas such as parks in addition to residential areas. All hawks avoided very open areas such as fallow agricultural fields. We observed no systematic use of bird feeders by Cooper's Hawks. In fact, visits by Cooper's Hawks to feeders were not statistically different from that expected by a null model based on random feeder visitations, a result consistent with our work on Sharp-shinned Hawks and the idea of "prey management" by Accipiter hawks. © The Cooper Ornithological Society 2008.