Prolonged offspring dependence and cooperative breeding in birds

It has been suggested that the evolution of cooperative breeding in birds is associated with unusually long periods of offspring dependence ; this appears paradoxical because cooperative breeders often produce more broods than their noncooperatively breeding relatives. I compared the duration of parental care between cooperatively and noncooperatively breeding species using phylogenetically independent contrasts and matched pairs. The incubation and nestling periods did not differ between the two parental care systems, but the duration of postfledging offspring care was significantly longer in species that regularly breed cooperatively. This relationship remained when other factors that are thought to affect the duration of fledgling care (breeding habitat, body size, latitude of breeding, diet) were controlled statistically. Cooperative breeders appear to provide more prolonged postfledging care because additional care providers reduce the costs of parenting, offspring have less incentive to become independent, and a division of labor can develop during reproduction—helpers continue to feed fledglings while breeders initiate the next nesting attempt.