Helping behavior in birds and mammals

Helping behavior occurs when an animal helps to rear the offspring of others by providing food, defense, or other forms of alloparental care to the brood. In birds and mammals, helpers are typically young animals who delay their own reproduction for at least one breeding season but eventually produce offspring later in life. Helpers in cooperative societies therefore differ from workers in eusocial societies such as those of ants, since they are not permanently sterile. Most cooperative breeders live in family groups in which helpers are related to the brood that they rear, but many societies also contain unrelated immigrants. When helpers are related to breeders, they can gain indirect fitness benefits (by increasing the reproductive success of their kin) that partially offset the direct fitness costs of delaying their own reproduction. Both related and unrelated helpers may also gain direct fitness benefits from group membership, including increased survival prior to dispersal and/or the opportunity to inherit their natal breeding territory. In some species, helpers may gain additional direct fitness by co-breeding with the dominant breeders, creating a continuum between cooperative breeding (in which helpers are non-reproductive) and communal breeding (in which multiple individuals reproduce in the same brood and cooperatively provide parental care). Helping behavior is often sex-biased, reflecting differences in dispersal patterns and differences in reproductive opportunities between males and females. Cooperative breeding has evolved many times in vertebrates and is unevenly distributed across lineages, leading to strong phylogenetic patterns. Large-scale comparative analyses have revealed that family living and constraints on independent reproduction – including a lack of reproductive opportunities and harsh or unpredictable environmental conditions that make it difficult to rear young alone – are associated with an increased likelihood of helping behavior.