Temporal tuning of homeward flights in seabirds

Timing is crucial for animals for optimizing foraging, travelling and breeding behaviours in spatiotemporally heterogeneous environments. Some seabirds, commuting between land-based nesting colonies and widely dispersed foraging areas at sea, return to their colonies within several hours after sunset. This temporal pattern raises the question of how they manage to time arrivals over largely variable homeward distances. However, no study has investigated their at-sea behavioural patterns associated with arrival times. To explore this question, we tracked breeding streaked shearwaters, Calonectris leucomelas, with GPS data loggers, which continuously recorded fine-scale movement paths during their trips. Shearwaters adjusted the onset of their homeward journeys according to wide-ranging distances between their chosen foraging areas and breeding colonies, leaving earlier from further locations. The start time of homing was pushed forward correlating with the increased travel time expected from their homeward distance and average movement speed. This resulted in arrivals at the colony concentrated within a few hours after sunset independent of the distances. To our knowledge, similar temporal tuning of homing trips has not been reported previously. The strong correlation between the timing and distance of homeward journeys implies this behaviour is ecologically important. Further experiments will help clarify its generality in the animal kingdom as well as proximate mechanism(s) and ultimate function(s).