The Role of Neophobia in Determining the Degree of Foraging Specialization in Some Migrant Warblers

Abstract

Experiments were conducted to examine the psychological basis of foraging specialization in Dendroica warblers [D. magnolia, D. caerulescens, D. tigrina, D. coronata, D. pensylvanica, D. castanea]. The focus of the experiments was a comparison of wild-caught, immature bay-breasted and chestnut-sided warblers. During the nonbreeding season, the bay-breasted warbler is a generalized forager compared to the chestnut-sided warbler. Individuals of 4 other species of Dendroica were tested in similar experiments to see how bay-breasted and chestnut-sided warbers compared with the genus as a whole. Consistent with field observations, chestnut-sided warblers obtained hidden mealworms from fewer unfamiliar objects than did bay-breasted warblers. They approached a similar number of objects, but were more timid and ambivalent. When offered a variety of model microhabitats with a conspicuous and familiar reward, chestnut-sided warblers were far more hestitant to approach and would often not feed from novel microhabitats. Individuals of all 6 spp. of Dendroica had consistent rankings in how rapidly they fed at the model microhabitats. This variation had a species-specific component, with bay-breasted warblers feeding most rapidly and chestnut-sided warblers feeding most hesitantly. The number of microhabitats visited by a warbler is probably the result of a dynamic interaction of attraction and fear. Individuals and species with greater aversion to novel foraging situations may be more specialized than less neophobic warblers. Shifts in a neophobia threshold may provide a relatively simple mechanism for varying foraging specialization among closely related species.