Social transmission of egg rejection in a cuckoo host

Abstract

Social learning can enable the rapid dissemination of behaviours throughout a population. Rejection of foreign eggs is a key defence used by hosts of avian brood parasites, and although learning has long been recognized as an important factor in egg rejection decisions, the role played by social cues remain less well understood. Here, we aimed to determine whether access to social information influenced egg rejection behaviours in semicolonial barn swallows, Hirundo rustica . By manipulating the social information available from a neighbouring nest, we showed that swallows with access to social information (i.e. a neighbour that recently rejected an egg) were more likely to reject a foreign egg that those that did not have access to social information (i.e. a neighbour that did not reject an egg). A subset of nests were videorecorded, and in these recordings the rejections were always performed by the incubating parent rather than a conspecific. This study provides direct evidence that egg rejection behaviours can be informed by social information in the absence of brood parasites, and in doing so highlights the dynamic nature of the defences that hosts deploy against brood parasitism. • Information about parasitism risk can inform host defences. • We tested whether social information could inform egg rejection decisions. • Barn swallows with access to social information rejected more foreign eggs. • Our results highlight the role that social information can play in coevolution.