Ecological flexibility and selectivity in mixed-species flock participation in birds

Abstract

Mixed-species groups are hypothesized to allow animals to minimize competitive interactions and maximize facilitative interactions. Individuals participation in mixed-species groups may reduce rates of competition and increase the social information available about predators or food availability. Behavioral plasticity may further increase these benefits as plastic species alter their rates of niche overlap with group mates. We investigate two axes of behavioral plasticity that may modulate how species interact with group mates in mixed-species groups--flexibility and selectivity. Specifically, we assess avian species patterns of selective preferences for participation in flocks of certain strata and whether behavioral flexibility in foraging strata corresponds with the foraging strata of flock mates. All species in our study maintained or increased their foraging strata overlap with flock mates, supporting the hypothesis that facilitation plays an important role in flock formation. Notably, the methods that species used varied: some species moved closer to flock mates via flexibly matching their flock mates behavior, some showed selectivity for flocks of certain stratums, and others did both. Ultimately, we show that species balance facilitative and competitive interactions with flock mates via multiple methods and that consideration of behavioral plasticity is integral to understanding the nuances of mixed-species flock interactions.