The ontogeny of social skills: experimental increases in social complexity enhance reproductive success in adult cowbirds

The social environment can act as an important selective force on both morphological and behavioural traits by conferring a reproductive advantage on individuals that successfully navigate social interactions. The ontogeny of these social traits is poorly understood. We examined whether increasing exposure to more complex social environments could hone competitive skills and ultimately increase reproductive success in adult brown-headed cowbirds, Molothrus ater. We created two types of flocks (‘Dynamic’ and ‘Stable’) that differed in social complexity. In Dynamic flocks, birds were regularly exchanged across groups, whereas in ‘Stable’ flocks, the composition of birds remained static throughout a year. Social networking analyses revealed that males in the Dynamic flocks had larger and more variable singing networks during the manipulations than did the males in the Stable flocks. When we put males from the two conditions together into new environments with unfamiliar females, the Dynamic-condition males had greater mating success. Our results establish a link between social competence and reproductive success and suggest that social skills are extremely flexible characteristics, even in adulthood.