FORAGING BEHAVIOR OF CO-OCCURRING NEOTROPICAL RESIDENTS AND NON-BREEDING MIGRANTS, A PILOT STUDY IN PUNTA CANA

Niche partitioning, the division of resources among co-occurring species in a community to reduce interspecific competition, is an evolutionary process intensively studied in birds. It has been particularly well-studied in the New World Warbler family (Parulidae) since MacArthur's landmark study of breeding warblers in the United States. However, partitioning on warblers' wintering (non-breeding) grounds has received relatively little attention, especially in relation to potential competitive effects of the migrants on resident species. We hypothesized that reduced dry-season food availability at our study site in Punta Cana, Dominican Republic would promote foraging niche partitioning among insectivorous migrant and resident species. We gathered behavioral data on eight wintering migrant warbler species as well as two resident insectivores, Todus subulatus (Broad-billed Tody) and Vireo altiloquus (Black-Whiskered Vireo). For each foraging attempt, we recorded data on foraging height, technique, substrate, and habitat, as well as notes on social behavior. Of the 45 species-by-species pairings we evaluated, only two species pairings showed no significant average differences across any foraging variable. However, we found that midstory gleaning migrants occupied broad niches with substantial overlap. Resident species predominantly employed flycatching and berry consumption as foraging techniques, differing from migrants, which primarily gleaned insects. Among the migratory species, foraging substrates or heights were distinct across all pairwise comparisons except among American Redstart (Setophaga ruticilla), Prairie Warbler (S. discolor), Northern Parula (S. americana), and Cape-May Warbler (S. tigrina), which showed relatively similar behavioral foraging niches. Although our results are limited to a single site and a short sampling period, they suggest that within this spatiotemporal community there are substantial differences in behavioral foraging niches among residents and between migrants and residents. These findings provide insight into how migrant and resident birds seasonally coexist in this coastal dry insectivorous community.