Social Learning in Birds Studied by Cross-Fostering in the Wild

Abstract

Social learning is widespread in nature and important for the behaviour, ecology and conservation of animals. We applied a method of cross-fostering between passerine birds in woodland areas in Norway, including great tits Parus major, blue tits Cyanistes caeruleus, and pied flycatchers Ficedula hypoleuca. When cross-fostering between tit species, the offspring sexually mis-imprinted on the foster species. Survival rate was similar to the controls but mating success was strongly reduced and mixed pairings occurred between cross-fostered birds of the two species, resulting in one case of hybridization. Song was affected, but the extent showed great variation among males. Male pied flycatchers raised by tits also included strophes from the foster species in their song, in particular if they had been raised together with siblings of the foster species. However, surprisingly, in flycatchers, mate choice was not affected by cross-fostering, indicating a different mechanism between song learning and mate choice. In tits, choice of nest site was affected by the crossfostering, the birds taking characteristics of the natal nest site into account, and the behaviour of members of their foster parent species. Cross-fostering had a strong effect on foraging behaviour in terms of spatial location of foraging sites and the type of prey items provided to the young. Learning foraging techniques within the natal habitat may explain why prey provided by immigrant tits new to the study area differed from those provided by local recruits. We discuss how social learning may affect the evolution, behaviour and ecology of these birds, including the evolution of nest parasitism, and how cross-fostering among species may be used in management programs of endangered species.