Disentangling the relative contribution of predation avoidance and increased foraging efficiency in the evolution of sociality in animals has proven difficult given that the two types of benefits often operate concurrently. I identified different types of refuges from predation in birds related to morphological and ecological traits, providing an opportunity to examine concomitant changes in sociality over evolutionary times. Results of a matched-species comparative analysis indicated a reduction in the size of foraging or non-foraging groups but not complete disappearance under negligible predation risk. The results suggest that while predation avoidance is an important component in the evolution of sociality in birds, it is most probably not acting alone but rather in conjunction with other benefits such as increased foraging efficiency.
Keywords: birds, group size, predation risk, relaxed selection, sociality