The study, which provides a broad and comprehensive view of the migratory behaviour of these taxa, results from the scientific collaboration of up to 12 research teams from seven countries around the world.

Studying migratory connectivity to improve protection

Migratory seabirds spend most of their lives at sea; this is the case of the Scopoli’s shearwater (C. diomedea) cited in the study. Knowing their wintering areas — with all the existing connections with the different breeding areas — is a key factor in establishing conservation measures and designing efficient marine protected areas (MPAs). In these migratory species, the measure of the interconnection between the different breeding populations and the wintering populations is known as migratory connectivity.

The new study combines the estimation of migratory connectivity with the environmental habitat preferences of up to three shearwater species. “The results obtained help us to understand not only how the three species migrate and behave in wintering areas, but also how this migratory behaviour may have played a role in the evolutionary segregation of the three taxa”, says Raül Ramos, associate professor at the Department of Evolutionary Biology, Ecology and Environmental Sciences of the Faculty of Biology.

Integrating all the scientific data on the migratory connectivity of these oceanic birds as much as possible will help to manage conservation measures for the populations more effectively.

“When a species has high migratory connectivity, individuals breeding in the same populations or in proximity to each other also tend to winter together and different breeding populations do not tend to mix during wintering. Conversely, when migratory connectivity is low, individuals from different breeding populations mix in more or less common wintering areas”, explains Raül Ramos.

“In the case of seabirds, the impact of global warming or different human activities on the marine environment can alter the migratory connectivity of these species”, he continues. As the researcher Virginia Morera Pujol, first author of the study, points out, “if the protection measures are provided for a single wintering area for a species with very high migratory connectivity, the benefit for the species will be minimal”.

“In turn, disturbances in a specific wintering area of a species with high migratory connectivity could cause the local extinction of the species in one of its breeding populations because all individuals in that particular population would be affected”, she says.

Migratory behaviour and gene flow between populations

The study also reveals how the three shearwater species mostly preserve their migratory identity and explore quite different wintering areas.

“Despite this general behaviour, we have also found that birds breeding in the area of the Strait of Gibraltar (the contact area between the Atlantic and Mediterranean species) show an intermediate migratory behaviour between the two taxa. This result would indicate some gene flow between these two shearwaters, and that the segregation of the three species was probably facilitated, in part, by differences in migratory behaviour”, stresses Professor Jacob González-Solís, head of the Seabird Ecology Lab.

From the Mediterranean to the American shores

The paper warns that the wintering areas described have high fishing pressure, which makes wintering seabirds more vulnerable to bycatch. Other non-lethal disturbances have also been identified, such as overfishing and a reduction in available food, which could be indirect causes of population decline in the medium and long term. “This is particularly critical for the Cape Verde Cory’s shearwater, a species endemic to the archipelago and which only breeds on these islands. Our study shows that the only wintering area for this species is on the Argentinean and Brazilian coasts, and therefore any disturbance in this area would be very detrimental to the entire species”, warn the authors.

The necessary internationalization of migration studies

Access to oceanic birds for the study of their movements is one of the great obstacles to scientific activity. In the last couple of decades, new remote tracking technologies — with small, lightweight devices so as not to hinder the birds’ manoeuvrability — have facilitated fieldwork and the study of these oceanic birds, which are only accessible during the breeding season, when they incubate their clutches and breed in deep burrows, usually on islands and islets that are usually uninhabited. International collaboration has made it possible to address the cost and logistics required for this study, which puts the conservation and protection of seabirds with a wide geographical range at the centre of interest, thanks to the enormous volume of data contributed by different teams from all over the world.