Researchers have shown the flexibility of individual Balearic Shearwaters is pushing the species’ non-breeding range further north in response to climate change.

The study, published in Proceedings of the National Academy of Sciences,has shone light on the rapidly changing post-breeding distribution of the Critically Endangered seabird.

Balearic Shearwater’s perilous conservation status is blamed on fisheries that drive mortality through bycatch, with the birds getting caught on hooks and in nets. Outside of the breeding season, the birds spill out of the Mediterranean to feed in the open ocean off western Europe

Individual Balearic Shearwaters have been moving an average of 25 km further north every year after breeding, but the longer migration could have hidden costs (Jon Mercer).

This individual flexibility was discovered by the researchers at the University of Oxford and the University of Liverpool, who started fitting Balearic Shearwaters with geolocator devices at breeding colonies in Mallorca in 2010.

Balearic Shearwaters are increasingly seen in large numbers further north in Europe. Until now, it had been unclear whether natural selection was driving the rapid shift, or individual flexibility.

Tracking the same individuals over the course of several years proved that there was considerable individual flexibility in the shearwaters’ post-breeding movements and that the shift in range was not driven by evolution. Each year, individual shearwaters moved an average of 25 km further north.

Joe Wynn, co-lead author of the study, said: “We found that the best predictor of this change in migratory behavior was the average sea surface temperature in the summering grounds, suggesting that the birds may well be following changes in underlying marine resources. The fact that individuals can be this flexible in the face of rapid climate change is encouraging.”

Although it appears that individuals are more capable of adapting to the effects of climate change than previously thought, it is possible that the shift in range and the greater distance between breeding and non-breeding areas may have hidden costs for the species in the long term.

Professor Tim Guilford, co-author of the study, explained: “We found that individuals speed up their return migration the further north they have gone, but this only partially compensates for the extra distance and they still arrive back in the Mediterranean late. We don’t yet know how such delays may affect their breeding success or survival.”

The findings could inform conservation strategies for a range of migratory species affected by climate change, not only for Balearic Shearwater.