Effect of Vegetative Cover on Foraging Site Selection by Swainson's Hawk

If plant cover limited the productivity of potential hunting sites, a reduction in a habitat's cover would increase its use by foraging hawks, and predator-prey models that assume a direct relationship between hunting and prey density would need to be reconsidered when applied to raptors.

Abstract

Foraging bouts of male Swainson's Hawks (Buteo swainsoni) were observed using radio-telemetry to determine the effect of plant cover on the selection of foraging sites. Home ranges consisted of varying amounts of cultivated and uncultivated habitats. Cultivated fields were the most abundant and they supported large amounts of prey, but were not hunted until crop harvest reduced the density of their plant canopy. A negative correlation between estimates of plant cover and foraging suggested that habitat differences such as vegetative cover were of greater importance than prey density in the selection of hunting sites. A correlation between foraging and prey biomass after it had been adjusted for vegetative concealment indicated that models relating prey abundance with raptor foraging should consider the effect of such a habitat difference on the availability of a hunting site's food supply.