Sociality in Birds

Abstract

Birds differ from the other groups discussed in this book not via any single feature but by often combining four unusual traits. First, most birds fly, which enhances' their ability to choose where they breed and forage, activities that they therefore can, at least potentially, do in very different areas. For example, some albatross travel more than 10,000 kilometers to gain food to provision their young. Second, birds are homeotherms and maintain a very high body temperature, so the metabolic investment that is required to rear offspring to independence is extremely high. Third, unlike most of their homeothermic mammalian counterparts, males and females can share much of this expensive parental care, as both sexes can incubate and provision offspring. Finally, again unlike most mammals, in birds male offspring are more likely to be philopatric than females (Greenwood, 1980; Mabry, et al., 2013), and hence more likely to spend much of their lives in close proximity to their relatives. At least in part because of this combination of features, birds live social lives to an extent that is rare among animals. Birds cooperate to obtain mates, to obtain food, to fly more efficiently, and to evade predators. In addition, most species form pairbonds, and males and females rear young collaboratively, which itself is a form of relatively advanced social organization (Lack, 1968). Because a review of all aspects of sociality, including the evolution of pair-breeding, is beyond the space allocated to this chapter, here we concentrate primarily on an advanced form of sociality: cooperative breeding, in which more than a pair of individuals cooperate in some way to raise young. There is some disagreement in the literature over how avian cooperative breeding should be defined. One definition restricts the term to the case where some group members contribute parental care but do not themselves gain parentage