Habitat and body condition influence American Redstart foraging behavior during the non-breeding season

Abstract

Insectivorous birds may adjust their foraging strategies to exploit changes in resource distributions. Arthropod prey strongly influence habitat-specific persistence of long-distance migrant passerines in their wintering areas, and arthropods are strongly affected by rainfall. However, the effect of drought on the dynamics of avian foraging ecology as resources shift is not well understood. We captured female American Redstarts (Setophaga ruticilla) and studied their foraging behavior in high-quality (evergreen black mangrove) and low-quality (deciduous scrub) habitat in Jamaica during the winter of 1995-1996. As is typical in southwestern Jamaica, conditions became drier as spring approached and many trees in scrub lost most of their leaves; mangrove trees maintained most of their leaf cover. Birds in scrub lost more mass than those in mangrove, and scrub birds shifted to using more aerial (and fewer near-perch) maneuvers. In scrub, but not in mangrove, the proportion of wing-powered movements and aerial foraging maneuvers was positively correlated with mass corrected by body size. In both habitats, attack rate was negatively correlated with body condition. Therefore, redstarts in scrub that maintained body condition were likely better able to use energetically expensive aerial maneuvers and wing-powered search movements to exploit large, calorie-rich flying arthropods. As the scrub dried over the course of the winter, the shift in foraging tactic may have allowed some birds to forage more efficiently (i.e., lower attack rate), likely facilitating maintenance of good body condition.