Data from: Positive relationships between association strength and phenotypic similarity characterize the assembly of mixed-species bird flocks worldwide

Competition theory predicts that communities at small spatial scales
should consist of species more dissimilar than expected by chance. We find
a strikingly different pattern in a multi-continent dataset (55
presence-absence matrices from 24 locations) on the composition of
mixed-species bird flocks, important subunits of local bird communities
the world over. Using null models and randomization tests followed by
meta-analysis, we find the association strength of species in flocks to be
strongly related to similarity in body size and foraging behavior, and
higher for congeneric compared with non-congeneric species pairs. Given
the small spatial scale of our individual analyses, differences in habitat
preferences of species are unlikely to have caused these association
patterns; therefore, the patterns are most likely the outcome of species
interactions. Extending group-living and social information use theory to
a heterospecific context, we discuss potential behavioral mechanisms
leading to positive interactions among similar species in flocks as well
as ways in which competition costs are reduced. Our findings highlight the
need to consider positive interactions along with competition when seeking
to explain community assembly.