Songbird parents coordinate offspring provisioning at fine spatio-temporal scales.

For parents, rearing offspring together is far from a purely cooperative exercise, as a conflict of interest ('sexual conflict') exists over their optimum level of care. Recent theory emphasizes that sexual conflict can be evolutionarily resolved, and complete parental cooperation can occur, if parents directly respond ('negotiate') to each other and coordinate their level of care. Despite numerous experiments showing that parents are responsive to each other, we still lack empirical evidence of the behavioural mechanisms by which this negotiation occurs. In this study, we investigated the spatio-temporal coordination of parental provisioning behaviour as a possible mechanism of negotiation over parental care. We deployed an automated radiotracking technology to track the provisioning activity of wild great tit Parus major pairs during chick rearing. Our analyses represent the first detailed spatial and temporal description of foraging coordination in songbird parents in a natural context. We demonstrate that the foraging behaviour of the two parents is highly coordinated in space and time, with parents changing their foraging locations in conjunction with their partners' movements. Therefore, foraging coordination could be a mechanism by which parents directly monitor and respond to each other's level of investment.