Social foraging and the evolution of white plumage

The significance of social foraging to the evolution of avian plumage trait s has received little attention. White plumage could increase conspicuousne ss against a dark background and serve as a passive recruitment signal to a ttract distant foraging companions. White plumage could thus be selected if white individuals obtain net fitness benefits by attracting conspecifics t o feeding flocks. Species that benefit little from the presence of foraging companions should have a darker, more cryptic coloration to avoid attracti ng potential competitors. Flash marks - white patches on wings or tails, of ten hidden until individuals take flight - could also be more common in soc ial species if such marks serve to increase flock cohesion. In a data set i ncluding pairs of closely related species with contrasting foraging sociali ty, social species possessed overall whiter plumage than non-social species but did not exhibit a higher frequency of flash marks. Several traits, suc h as habitat type, plumage dichromatism, male body mass, sexual size dimorp hism, prey type, level of prey activity and social mating system, which cou ld all influence plumage characteristics on their own, were not related to social foraging or to the expression of plumage traits. This study provides empirical support across a wide range of species for a relationship betwee n social foraging and white plumage coloration in birds.