Coordination of care is facilitated by delayed feeding and collective arrivals in the long-tailed tit

When multiple carers invest in a shared brood, there is likely to be conflict among individuals over how much each carer invests. This conflict results in suboptimal investment to the detriment of all carers. It has been proposed that conditional cooperation, that is, ‘turn taking’ or ‘alternation’, may resolve this conflict by preventing exploitation. This contentious idea has received some empirical support, but distinguishing active alternation from that expected via passive processes has proved challenging. The aim of this study was to use detailed observations of provisioning to examine whether carers at biparental (parents only) and cooperative (parents and helpers) nests of the long-tailed tit, Aegithalos caudatus, behave in a context-dependent manner that increases the level of alternation. First, we show that carers that had been the last to feed waited near the nest (loitering) for longer before feeding when they next arrived at the nest and allowed others to feed first, thus facilitating alternation. Second, we found that the arrival of carers near the nest and their subsequent feeds were tightly synchronized, with overlapping loitering periods, allowing them to monitor the effort of other carers. Finally, we show that measures of coordination were influenced by carers arriving in a status-dependent order, with breeding females consistently arriving first and helpers last. Together, these results show how patterns of alternation and synchrony arise in long-tailed tits, and reveal the behavioural mechanisms underpinning coordination of care.