Balearic shearwaters have a remarkable response to climate change

A new study led by the University of Oxford offers a new perspective on how animals are responding to the challenges posed by climate change. The research was focused on the remarkable adaptability of Europe’s most endangered seabird, the Balearic shearwater (Puffinus mauretanicus).

“How individual animals respond to climate change is key to whether populations will persist or go extinct. Yet, few studies investigate how changes in individual behavior underpin these population-level phenomena,” wrote the study authors.

“Shifts in the distributions of migratory animals can occur through adaptation in migratory behaviors, but there is little understanding of how selection and plasticity contribute to population range shift.”

Behavioral adaptability 

The experts found that the rapid migratory range shift of the Balearic shearwater is primarily due to individual behavioral flexibility rather than evolutionary selection.

The significance of this finding lies in its implications for conservation strategies of vulnerable migratory bird species.

The research also suggests that animals may possess more behavioral adaptability to respond to climate changes than previously believed.

However, this adaptability might come with hidden costs, leaving the long-term effects on the Balearic shearwaters uncertain.

Focus of the study

Known for their longevity, Balearic shearwaters are currently classified as critically endangered, largely due to declines associated with fisheries by-catch.

These seabirds breed in the secluded areas of the Mediterranean’s Balearic Islands and migrate to the Atlantic coasts of Spain, France, and increasingly the UK for summer.

The shift in their migration patterns was discovered through a collaborative effort involving researchers from the University of Oxford’s Biology Department, the University of Liverpool, and other collaborators in Ibiza. 

Shifting migration patterns 

Since 2010, the experts have been tracking colonies in Mallorca using state-of-the-art miniature geolocation devices. These devices revealed a consistent northward migration trend, with an average shift of 25km per year.

“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,” said study co-lead author Joe Wynn.

Breeding delays

Despite their flexibility in changing summer destinations, Balearic shearwaters face constraints regarding their breeding locations. This means that migrating further north results in a longer journey back in the autumn. 

“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,” explained study co-author Professor Tim Guilford.

Long-distance navigation

The study also delved into the intriguing aspect of how these birds navigate such long distances. 

“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,” said study co-lead author Patrick Lewin.

“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.”

“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.”

Study implications 

Balearic shearwaters, part of a highly threatened group of birds, face a multitude of threats including predation, habitat degradation, fisheries bycatch, overfishing, pollution, and windfarm development. 

“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,” said study collaborator Pep Arcos, SEO at Birdlife.

“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.”

The study is published in the journal Proceedings of the National Academy of Sciences.

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