Variable postfledging care in a cooperative bird: causes and consequences

Prolonged postfledging care is a commonly observed behavior in many cooperatively breeding species and has been shown to provide young with both survival and developmental benefits. However, the causes of intraspecific variation in postfledging care and the consequences of this variation on the development of young remain unclear. Here we investigate factors affecting the duration of postfledging care in the cooperatively breeding pied babbler (Turdoides bicolor). We show that the duration of care is variable (40--97 days) and is determined primarily by the cost of care. Adults in groups with a low adult:fledgling ratio were unable to maintain body mass during the period of chick provisioning and subsequently ceased care of young earlier. This had a strong influence on offspring development: fledglings that received longer periods of care attained higher foraging efficiency and body mass than their counterparts at 6 months of age. The duration of postfledging care also had long-term effects, with individuals that received longer periods of postfledging care more likely to successfully disperse from their natal group. This had important fitness implications as successful dispersers became reproductively active at an earlier age than their "failed-disperser" counterparts. These findings highlight the importance of considering long-term influences when assessing the benefits of prolonged postfledging care on offspring fitness and development in cooperative societies. Copyright 2007, Oxford University Press.