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 extensively studied in birds. It has been particularly well-studied in the New World Warbler family (Parulidae) since MacArthur's research on breeding warblers in the United States. However, partitioning on warblers' wintering (non-breeding) grounds has received relatively less attention, especially in relation to potential foraging niche overlap between migrants and resident species. We characterized foraging niche structure among eight wintering migrant warbler species and two resident insectivores, Todus subulatus (Broad-billed Tody) and Vireo altiloquus (Black-whiskered Vireo), in Punta Cana, Dominican Republic, during the dry season. Using standardized behavioral observations of foraging attempts, we recorded foraging height, technique, substrate, and surrounding canopy height, as well as notes on social behavior. We analyzed 665 foraging attempts from 276 individuals across 10 focal species and quantified pairwise niche overlap using Pianka’s index across four foraging axes. Composite overlap was low for the resident–resident pair and for all resident–migrant pairings. Strength of partitioning was more variable among migrant–migrant pairs: 17 of 28 pairings showed low overlap (0.6), with the highest overlap concentrated among midstory twig/leaf-gleaning warblers. For all low- and moderate-overlap pairings, statistical tests detected significant differences in at least one foraging axis; only two high-overlap migrant pairings showed no detectable differences across the measured axes. Although our results are limited to a single site and a short sampling period, they indicate clear resident-resident and resident-migrant differentiation and more variable structure among migrant species. Substrate use and foraging technique contributed more strongly to differentiation than vertical stratification alone. These findings provide the first quantitative description of behavioral niche structure within this resident-migrant assemblage in Hispaniola’s dry coastal forest.