Female social networks influence male vocal development in brown-headed cowbirds, Molothrus ater

Previous work has found that adult female brown-headed cowbirds, who do not sing, shape male vocal structure when in restricted housing. The present work extends this finding to a flock setting to examine the role of social behaviour in shaping male vocal development. We housed juvenile males with either adult or juvenile females in large flocks. Over the course of a year, we recorded their song and social behaviour. We found in early autumn that juvenile males housed with adult females improvised more song elements than males housed with juvenile females. During late autumn, we switched the males across female age-class conditions for 6 days. The males switched to the adult female flocks increased the number of improvised elements in their vocal repertoires. Analysis of the sequences of female–male social contact revealed that juvenile females, but not adult females, interacted indiscriminately with the males. Social network measures such as betweenness and closeness centrality further showed that adult females are more selective in their interactions with males than juvenile females. This study suggests a systemic role for selective social behaviour in shaping male vocal development.