Body mass, diet, foraging strata and foraging behaviour predict variation in the propensity to join mixed‐species flocks across birds

Abstract

Mixed-species flocking is common in birds and is associated with increased foraging efficiencyand reduced predation pressure. The propensity to join mixed-species flockswithin a community varies across species, possibly reflecting species-specific needs forincreased protection from predators, opportunities to increase foraging efficiency or both.Previous studies on predictors of mixed-species flocking propensity across species havetypically focused on local communities, with or without accounting for phylogeneticrelatedness. Here, we examined predictors of mixed-species flocking propensity acrossthe published literature using a phylogenetic linear mixed model framework. Weobtained 724 mixed-species flocking propensity estimates from 31 different study siteslocated primarily in South America and East Asia. Flocking propensity was associatedwith diet, foraging strata and foraging behaviour, and was inversely related to body mass.Controlling for phylogeny and body mass, flocking propensity was significantly lower fornectarivores than for species with other diets, lower for species foraging on the groundthan in higher strata, and lower for sallying species than for bark and near-perch foragers.These results suggest that variation across species in the tendency to join mixed-speciesflocks can be predicted from knowledge about various species-specific ecological traits inbirds.