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Many species that provide care for their offspring in tandem with a partner coordinate their activities to maximise the efficiency of their investment. However, it is not well known exactly how this coordination is achieved. Manx shearwaters Puffinus puffinus are Procellariiform seabirds that exhibit a dual foraging strategy during chick provisioning in which long foraging trips to maintain condition are alternated with short, frequent trips to feed the offspring. This strategy is employed in a coordinated manner between the parents, with one making short trips while the other takes a single long trip. Previous work revealed that a complementary switch in foraging trip type is initiated by the parents following a synchronous visit to the nest. We used a combination of observational data and experimental manipulation to examine the mechanisms that may underlie this behaviour. Specifically, we investigated the evidence that physical reunion is necessary to induce a switch in trip type, whether parents change their behaviour to maximise the probability of partner encounter, and whether indirect cues gained from the chick could inform a switch in behaviour. In our experimental approach, we manipulated the information adults had available to them by supplementarily feeding chicks to alter their begging behaviour. We found no support for the role of physical reunion or indirect cues in the coordination of care in this species. We discuss the possibility that the patterns of alternated provisioning observed during chick rearing in Manx shearwaters may emerge through entrainment during the well‐coordinated incubation period preceding chick provisioning.

Seabirds care for their offspring in remote breeding colonies where foraging sites are distant and may be unpredictable, and where chicks are left unaccompanied for extended periods during their parents’ foraging trips, leaving them vulnerable to predation or starvation. One way to mitigate this risk is for individuals to coordinate parenting duties with their partner. Many biparental and cooperatively breeding species are now known to coordinate their care, though the mechanisms underlying this are not well understood. In Manx shearwaters (Puffinus puffinus), both parents alternate shifts of incubation in a coordinated manner. To resolve which processes may underlie this routine, we imposed a wing-loading handicap on parents to reduce their foraging efficiency, forcing them to choose between an extended foraging trip or to return to the nest before their condition has recovered to optimal levels. We found that handicapped parents took significantly longer trips than normal, to which their partner responded by lengthening their incubation shift, suggesting shift durations are not pre-determined. However, the duration of foraging trips and the mass at which foraging birds returned to the nest appeared to be mediated by the condition of the partner. These results suggest that while foraging trip duration is largely driven by the need for the foraging bird to recoup its own condition losses, information-transfer between the parents may facilitate a more cooperative mechanism whereby the decisions made by foraging birds still account for the condition of their partner.