BREEDER-HELPER-INTERACTIONS IN THE PIED KINGFISHER REFLECT THE COSTS AND BENEFITS OF COOPERATIVE BREEDING

In most social species that is not only cooperation but also conflict between group members. Although various theoretical models have specified the conditions for, and the extent and direction of conflict and cooperation, there are few empirical data to test their predictions. This paper reports such a test for the pied kingfisher (Ceryle rudis), a cooperatively breeding bird species with two types of male helpers: primary (= related) and secondary (= unrelated). In a breeding colony at Lake Victoria (Kenya), the birds were studied with regard to: (a) aggressive and non-aggressive interactions between breeders and helpers before and after chicks hatched; (b) frequency and effect of prey transfer from helpers to breeders; and (c) sizes and types of prey brought to females and nestlings. It is concluded that all behavioral interactions and food contributions closely reflect the costs and benefits of giving and receiving help, which vary with the sex of the breeder, the relatedness between the group members, and the period of the reproductive cycle.