Annual Temperature Variation, Not Number of Predators, Predicts Variation in Foraging Group Size Among Pigeons Worldwide.

Many life history traits show predictable patterns at broad biogeographical scales, yet much less is known about how behavioural traits vary across such gradients. In this study, I investigated global variation in foraging group size within a large, cosmopolitan avian family-the pigeons-and assessed the roles of climate and predation in shaping these patterns. I compiled data from the literature for species occurring across a range of latitudes, altitudes, and habitats (islands v. continents) and analyzed the data within a phylogenetic framework that accounted for both biogeographical and ecological drivers of group size. Foraging group size increased with latitude among continental species but did not follow these trends on islands, where groups were generally smaller. Group size also increased at higher elevations. Among the climatic variables examined, annual temperature variation emerged as the strongest latitudinal predictor: greater temperature variability was associated with larger group sizes in continental species, but not in island species. The number of predators within a species' breeding range showed no significant relationship with group size. These findings suggest that climatic variability, rather than number of predators, is a key driver of foraging group size in pigeons at the biogeographical scale.