Task partitioning increases reproductive output in a cooperative bird

Parents often face a trade-off between the quality and quantity of young produced because terminating investment in current young could result in lower survival and future reproductive success, whereas initiating new breeding attempts could result in greater production of young. In cooperatively breeding species, helpers may alleviate this trade-off by assuming the role of primary caregivers to first broods, liberating breeders to initiate subsequent breeding attempts without compromising the level of care offspring receive. Here, we investigate the occurrence and consequences of brood overlap in the cooperatively breeding pied babbler (Turdoides bicolor). Brood overlap occurred only in groups and resulted in breeders primarily investing in second broods while helpers continued to provide care to first broods, resulting in dependent young from overlapping broods being raised simultaneously. Interbrood partitioning of care during brood overlap resulted in a greater production of young per season in groups (cf., pairs) without any effect on offspring survival, thus representing a reproductive benefit of task partitioning in cooperatively breeding species.