Effects of food availability on the distribution of migratory warblers among habitats in Jamaica

1. Theoretical arguments suggest that distributions of migratory birds in winter should match patterns of food availability, but in reality the match between migrants and their food may be imperfect because, for various reasons, birds may be unable to 'track' food resources. We tested the hypothesis that food availability influences the distribution of migratory canopy-foraging insectivorous warblers wintering in Jamaica. 2. Over a wide spatial scale (24 sites on the island), warbler abundance varied significantly among sites and habitats and was significantly dependent on measures of arthropod biomass. Alternative factors (vegetation characteristics, resident bird competitor abundance, predator abundance) were not correlated with warbler abundance. 3. Over a short temporal scale (about 2 weeks) at a single site, warbler abundance increased as predicted quantitatively after a natural, rapid increase in arthropod biomass. 4. Over a longer temporal scale (the duration of a winter), changes in density and persistence of individually marked American redstarts (Setophaga ruticilla, L.) on six sites corresponded with concurrent fluctuations in arthropod biomass. 5. These results document a strong association between arthropod biomass and warbler abundance in time and space, suggesting that warblers wintering in Jamaica distribute themselves in response to food resources. 6. We hypothesize that dominance hierarchies and variable movement strategies operate in concert with birds' responses to food to influence the distribution of wintering warblers at different spatial scales. Whether food availability determines habitat quality remains to be investigated.