Navigational control of avian migration is understood, largely from the study of terrestrial birds, to depend on either genetically or culturally inherited information. By tracking the individual migrations of Atlantic Puffins, Fratercula arctica, in successive years using geolocators, we describe migratory behaviour in a pelagic seabird that is apparently incompatible with this view. Puffins do not migrate to a single overwintering area, but follow a dispersive pattern of movements changing through the non-breeding period, showing great variability in travel distances and directions. Despite this within-population variability, individuals show remarkable consistency in their own migratory routes among years. This combination of complex population dispersion and individual route fidelity cannot easily be accounted for in terms of genetic inheritance of compass instructions, or cultural inheritance of traditional routes. We suggest that a mechanism of individual exploration and acquired navigational memory may provide the dominant control over Puffin migration, and potentially some other pelagic seabirds, despite the apparently featureless nature of the ocean.

Lay SummarySex segregation, competition and differences in individual quality may drive dispersive migration in birds and affect their fitness. Atlantic puffins tracked for up to 6 years followed remarkably different migration routes, but individuals followed the same route every year. Although random dispersion and sex segregation could not explain the patterns observed, birds visiting the Mediterranean Sea foraged more and had a higher breeding success than birds remaining locally or visiting the Atlantic Ocean.

Many marine predators coexist at colonies, creating a zone where there could be significant inter-and intraspecific competition. To minimize the potential for direct competition, under the principle of competitive exclusion, sympatric predators may differ in their foraging behaviour at the colony. At Skomer, Wales, razorbills Alca torda and puffins Fratercula arctica both breed at the same time of year, forage on sand eels Ammodytes sp. and their populations are stable or declining, meaning that they may be close to carrying capacity and experiencing competition. To examine how they differ in their foraging behaviour, time-depth-temperature recorders were attached to the legs of chick-rearing individuals of both species. Puffins have lower wingloading and lower total oxygen stores than razorbills and are therefore expected to invest more time in flying and less time in diving than razorbills. Mean (±1 SE) dive depth was 11.8 ± 0.45 m for puffins and 8.2 ± 0.21 m for razorbills, while mean dive duration was 40 ± 0.45 s for puffins and 24 ± 0.21 s for razorbills. Both species spent most of their dive time making shallow, V-shaped dives during daylight hours. In contrast to our prediction, foraging behaviour was very similar between the 2 species, although puffins tended to spend more time both diving and flying. The higher diving and flying rates of puffins may be associated with multiple prey loading, as puffins tend to bring back smaller (and therefore more) prey items than do razorbills.

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Understanding the points in a species breeding cycle when they are most vulnerable to environmental fluctuations is key to understanding interannual demography and guiding effective conservation and management. Seabirds represent one of the most threatened groups of birds in the world, and climate change and severe weather is a prominent and increasing threat to this group. We used a multi-state capture-recapture model to examine how the demographic rates of a long-lived trans-oceanic migrant seabird, the Manx shearwater Puffinus puffinus, are influenced by environmental conditions experienced at different stages of the annual breeding cycle and whether these relationships vary with an individual’s breeding state in the previous year (i.e., successful breeder, failed breeder and non-breeder). Our results imply that populations of Manx shearwaters are comprised of individuals with different demographic profiles, whereby more successful reproduction is associated with higher rates of survival and breeding propensity. However, we found that all birds experienced the same negative relationship between rates of survival and wind force during the breeding season, indicating a cost of reproduction (or central place constraint for non-breeders) during years with severe weather conditions. We also found that environmental effects differentially influence the breeding propensity of individuals in different breeding states. This suggests individual spatio-temporal variation in habitat use during the annual cycle, such that climate change could alter the frequency that individuals with different demographic profiles breed thereby driving a complex and less predictable population response. More broadly, our study highlights the importance of considering individual-level factors when examining population demography and predicting how species may respond to climate change.