Provisioning of nestlings by dunnocks,Prunella modularis,in pairs and trios compensation reactions by males and females

Summary The mating systems in a population of dunnocks included monogamy, polygyny, polyandry and polygynandry. Broods were provisioned by lone females, by females with the part-time help of one male, by females with the full-time help of one male (pairs) or by females with the part-time or full-time help of two males (trios). We compared provisioning of nestlings in these different systems and used the results of natural and experimental removals to examine how individuals reacted to the provisioning by others. In pairs, males and females provisioned at similar rates (Fig. 2a). In trios, females and alpha males fed chicks at the same rate, and at a higher rate than beta males (Fig. 2b). Females attained maximum male help when two males shared provisioning equally (Fig. 6). Females were more likely to achieve this when they were able to escape alpha male guarding during the mating period and exercise some control over mating access by the two males (Fig. 7). Female provisioning did not increase when their help was reduced from two males to one (Fig. 4 a), but it did increase when male help was further reduced to either one male's part-time help (Fig. 5 a) or no male help (Fig. 3 a). Beta males increased their provisioning rate when alpha males were removed from a trio (Fig. 4b). Alpha males may have increased their rate when beta males were removed but any reaction was small. When one male was removed from a trio, the remaining male's provisioning rate was as expected for a male in a monogamous pair. When reactions occurred, they were not sufficient to compensate for the loss of the removed adult and nestling weight was reduced. We discuss the relevance of these results to the maintenance of parental care by pairs and trios.