Individual behavioural flexibility is more important to drive Balearic shearwaters north than evolutionary changes, according to a study published in the journal Proceedings of the National Academy of Sciences. The authors believe animals may have greater behavioural flexibility to respond to climate change impacts than previously thought.
How each animal reacts to climate change is key to determine whether they will survive or go extinct. Many species change their range as the temperature increases, but researchers haven’t unveiled the mechanism behind this shift.
One of Europe’s most endangered seabirds is the Balearic shearwater (Puffinus mauretanicus). Now, this study, led by biologists from Oxford University, UK, has found that individual flexibility is more important than evolutionary selection to guide this species rapid migratory range shift, but this adaptation may have hidden costs, making the long-term impact on this species unclear. The authors hope these findings could help inform conservation strategies for vulnerable species.
Balearic shearwaters are critically endangered because of a decline caused by fisheries by-catch. These birds frequently get caught on baited longline hooks and gill nets. They breed in remote areas of the Mediterranean’s Balearic Islands and spend the summer off the Atlantic coasts of Spain, France, and, increasingly, the UK.
Since 2010, a team from Oxford University and the University of Liverpool has been tracking colonies of these birds in Mallorca using on-board geolocation devices. This 14-year study showed that the birds have been migrating further north once they leave the Mediterranean. It was unknown, however, whether this change is driven by individual birds altering their behaviour, or natural selection “picking” birds that travel further.
To answer this question, the team compared the migration routes of the same individuals over multiple years. This revealed that each bird can shift their range northwards by an average of 25km per year.
“We found that the best predictor of this change in migratory behaviour 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,” said author Joe Wynn from the Department of Biology, University of Oxford & Institute of Avian Research “Vogelwarte Helgoland.”
The study also showed that despite the flexibility to migrate, Balearic shearwaters are more constrained when it comes to breeding, which means if they fly further north in the summer, they have to extend the journey when they return in the winter.
“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,” said Professor Tim Guilford from the Department of Biology, University of Oxford.
This raises interesting questions regarding how birds know how far they’ve traveled and how they return to the colony. To investigate this matter, the authors compared the distances of the different kinds of “maps” these birds may use to guide their migration routes.
“We found that the route individual birds took on previous migratory journeys was a much better predictor of return speed than an estimate of the straight line distance back to the colony. This suggests that birds do not rely on a large-scale navigational map on migration, but instead have some memory of the route they have flown in the past,” said Patrick Lewin from the Department of Biology, University of Oxford. “It is possible that individual route memory plays an important role in the migration of many other long-lived seabirds, but further research is needed to clarify this.”
“In addition to direct threats both on land and at sea, the increasing threat of climate change poses a challenge for a species that breeds in such a restricted habitat. Results from this study suggest that individual flexibility might help with distribution shifts driven by climate change outside the breeding season, but the question is still open about what might be the consequences of climate change for the birds during breeding when their movements are constrained by the location of the colony,” said collaborator Pep Arcos from SEO/Birdlife.
Lewin PJ, Wynn J, Arcos JM, Austin RE, Blagrove J, Bond S, Carrasco G, Delord K, Fisher-Reeves L, García D, Gillies N, Guilford T, Hawkins I, Jaggers P, Kirk C, Louzao M, Maurice L, McMinn M, Micol T, Morford J, Morgan G, Moss J, Riera EM, Rodriguez A, Siddiqi-Davies K, Weimerskirch H, Wynn RB, Padget O. Climate change drives migratory range shift via individual plasticity in shearwaters. Proc Natl Acad Sci U S A. 2024 Feb 6;121(6):e2312438121. doi: 10.1073/pnas.2312438121