Flocking and foraging behavior of wintering Prothonotary Warblers

We quantified flocking behavior and examined the impact of social context ( solitary, single species flocks, and mixed-species flocks) on the foraging behavior of Prothonotary Warblers (Protonotaria citrea) wintering in a Cost a Rican mangrove forest and surrounding habitats. Based on observations col lected over two winters during 70 visits to four sites, 87% (483) of the 55 5 Prothonotary Warblers encountered moved in hocks and over 48% (271) of th ese individuals were in single-species flocks. Although the propensity to j oin Rocks was 6% higher for Prothonotary Warblers in the second winter of t he study, neither the average size of single-species flocks nor the average number of individuals or species in mixed-species flocks differed between years. Twenty-seven different species were identified in mixed-species Rock s that had at least one Prothonotary Warbler, but Nearctic migrants dominat ed these flocks. Analyses of focal observations on 57 females and 93 males indicated that Prothonotary Warbler foraging behavior was largely independe nt of flock type and size. Foraging maneuver, substrate, and location did n ot differ significantly for individuals of either sex foraging alone, in si ngle-species, or mixed-species flocks. The species is almost strictly insec tivorous, gleaning made up 70% of 150 prey capture attempts observed and ab out half of all attempts (76 of 150) were directed towards leaf surfaces. F oraging generally occurred in the outer third of the tree, on branches less than 1 cm in diameter, in the bottom half of the canopy. Agonistic interac tions among flock members that involved Prothonotary Warblers were uncommon and neither fleck type nor size were useful predictors for rates of foragi ng, movement, preening, or vigilance.