We quantified foraging rates and foraging visibility metrics for four Neotropical warblers—Slate-throated Redstart (Myoborus miniatus), Golden-crowned Warbler (Basileuterus culicivorus), Wilson's Warbler (Wilsonia pusilla), and Black-and-White Warbler (Mniotilta varia)—under flocking and solitary conditions in western Panama to test hypotheses regarding the relative influences of predation pressure and social facilitation on foraging behavior. We also compared foraging behavior in primary forests and in traditionally managed shade coffee fields for two species (Slate-throated Redstart and Wilson's Warbler) to estimate spatial variation in foraging behavior and compare it to variation due to social situation (flocking or solitary). We then assessed the contribution of spatial variation in flocking propensity to the total spatial variation in foraging rates within species.

We observed very little overall within-species variability in foraging behavior between social situations or study locations. Only Slate-throated Redstart's behavior was consistent with the hypothesis that flock membership reduces predation pressure and therefore reduces the amount of foraging time spent being vigilant against predators, allowing birds to forage more quickly and find more prey items per minute. No species' behavior supported the hypothesis that flocking birds forage more efficiently than solitary birds by obtaining useful information from flock mates about the location or suitability of foraging resources or techniques.

The effort required to find prey items did not vary between study locations (forest and coffee field plots) for Wilson's Warbler. Because flocking also had no effect on foraging behavior of Wilson's Warbler, a reduction in flocking propensity in coffee habitat, relative to forest, did not cause further foraging behavior differences between study locations. Spatial variation in Slate-throated Redstart's foraging behavior independent of a flocking effect was minor; but flocking affected foraging rates, and flocking propensity was lower in coffee fields than in forest, so that location and flocking effects combined to widen foraging rate differences between locations. Thus, variations in flocking behavior and foraging behavior interacted differently for those two species.