EFFECTS OF WEATHER AND HABITAT ON FORAGING BEHAVIOR OF NON-BREEDING EASTERN PHOEBES

We investigated variation in foraging effort (horizontal distance traveled/number of foraging movements), percent of aerial hawking foraging movements (attempted capture of prey from air). mean perch height of sally initiation (height of perches from which sallies are initiated), and mean sally distance (distance from perch to prey) of non-breeding Eastern Phoebes (Sayornis phoebe) as a function of weather and habitat conditions. Only ambient temperature significantly correlated with foraging effort (r = -0.32, P = 0.02), indicating Eastern Phoebes expended more effort in search of prey under colder conditions. Both ambient temperature and distance to nearest water source significantly correlated with aerial hawking; however, the model containing only ambient temperature best explained variation in aerial hawking (r = 0.38, P = 0.008), indicating Eastern Phoebes attempted to hawk more prey from air at warmer temperatures. Mean perch height of sally initiation did not correlate (P > 0.05) with ambient temperature, wind speed. or vegetative density and dispersion. Mean sally distance did not correlate (P > 0.05) with ambient temperature, wind speed, or mean perch height of sally initiation but the natural log of sally distance correlated inversely (r = -0.48, P = 0.0004) with vegetative density and dispersion. The manner in which Eastern Phoebes alter foraging behaviors under varying environmental conditions, in conjunction with physiological adaptations, may be an important factor allowing this species to winter at higher latitudes than most other North American tyrant flycatchers and forage in multiple habitats. Received 21 November 2007. Accepted 3 August 2008.