The composition of mixed-species bird flocks in northern Australian savannas

The study of the ecology of species assemblages provides information on the function and resilience of ecosystems and helps predict the response of species to environmental change. Mixed-species flocks are a particular mode of avian assemblage and are suggested to have benefits for foraging and predator vigilance. In this study we examine for the first time the composition of mixed-species flocks in Australian savannas using data from 335 mixed-species flocks recorded across northern Queensland. A total of 122 species, both passerines and non-passerines, were observed in flocks. Individual flocks comprised 2-21 species and 2-237 individuals, with small, insectivorous birds dominant. Although flock composition was largely undifferentiated, six broad groups of mixed-species flocks were identified, their similarity driven by a few key species. Our study found that mixed-species flocks are a common component of the tropical savannas and are similar in individual bird abundance and richness compared with studies in other biomes. One important next step is to examine the relationship of mixed flocks to the entire species pool, and their ecological significance within tropical savannas.