Parents caring together for young must decide how large a share of the workload to make: on a behavioural time scale this may involve 'negotiation' in which each parent responds to the amount of effort by its mate in deciding on its own effort, while on an evolutionary time scale negotiation rules are in turn shaped by natural selection, including an evolutionary conflict of interest between the sexes ('sexual conflict') whereby each parent is selected to exploit the efforts of the other. In the last few years, theoretical studies have emphasized that the evolutionary outcome of sexual conflict depends critically on the behavioural mechanisms underlying negotiation, and empirical studies revealed that these mechanisms may involve a direct response to the partner's behaviour, - yet nothing more is known about such direct responses. We will use a state-of-the-art radio-tracking system to monitor the locations of pair members, and use this together with acoustic monitoring to gain unprecedented insights into the behavioural mechanisms underlying negotiation in great tit Parus major: To what extent is parental care coordinated in time and space? And how is parental care modified by the proximity or signalling of the partner? Moreover, we will test any responses to partner behaviour in mate removal experiments in which we observe parental care behaviour in the absence of the partner. This will not only significantly advance our understanding of negotiation over parental care, but also provide pointers for studies of more complex social networks.