Dietary opportunism, resource partitioning, and consumption of coffee berry borers by five species of migratory wood warblers (Parulidae) wintering in Jamaican shade coffee plantations

Diets reflect important ecological interactions, but are challenging to quantify for foliage-gleaning birds. We used regurgitated stomach samples from five primarily insectivorous species of long-distance migrant warblers (Parulidae) wintering in two moderate-elevation shade coffee farms in Jamaica to assess both foraging opportunism and prey resource partitioning.Our results, based primarily on 6120 prey items in 80 stomach samples collected during a one-week period in March 2000, confirm opportunism. The diets of all five warblers, including American Redstarts (Setophaga ruticilla), Black-and-White Warblers (Mniotilta varia), Black-throated Blue Warblers (S.caerulescens), Northern Parulas (S.americana), and Prairie Warblers (S.discolor), overlapped strongly based on consumption of the same prey types, even many of the same prey species (4 of 10 interspecific overlaps >0.9, range=0.74-0.97). Moreover, all five species fed on similarly small, often patchily distributed prey, including coffee berry borers (Hypothenemus hampei; Coleoptera, Curculionidae). Nonetheless, permutational multivariate analysis of variance also revealed that the diets of these species differed significantly, primarily with respect to prey mobility (winged vs. sessile); American Redstarts fed on the most mobile prey, and Northern Parulas on the least mobile prey and a relatively restricted set of prey taxa compared to the other four species of warblers. Overall, our results suggest both dietary opportunism consistent with a migratory life-history, and interspecific resource partitioning consistent with differences in morphology and foraging behavior during a food-limited season. Having provided evidence of the three necessary conditions, namely intraspecific competition, resource limitation, and interspecific overlap in resource use, the results of our study, in combination with those of other studies, also provide evidence of interspecific competition among wintering migrant insectivores. We thus argue that diffuse interspecific exploitative food competition may be more important than previously recognized.