Better understanding the wintering areas of migratory species of marine wildlife will be a critical factor in improving their conservation and protecting their key breeding grounds, particularly among seabird species already facing the squeeze of overfishing and the increasing risk of local extinction.

These are just some of a number of conclusions drawn by experts at the University of Barcelona who set out earlier this year to answer the question of what makes a good wildlife management plan and how critical is it that we consider the total range of migratory behaviour of marine wildlife and seabird species.

The paper has made the cover of the most recent edition of Diversity and Distributions as experts from the Seabird Ecology Lab of the Faculty of Biology and the Biodiversity Research Institute of the University of Barcelona dive into an analysis of one of the largest and most comprehensive databases ever compiled on the migratory behaviour of Cory’s shearwater.

The study analyses some 1,346 migratory movements of 805 individuals from 34 breeding colonies of three closely related Cory’s shearwater species: the Mediterranean Cory’s shearwater, the Atlantic Cory’s shearwater, and the Cape Verde shearwater.

This is the first paper to assess the migration and environmental preferences throughout the breeding range of the three species and one that called upon the expertise of 12 research teams from seven countries across the globe. 

Studying migratory connectivity to improve protection

As is the case with most species of migratory seabirds, the Cory’s shearwater spend most of their lives at sea. Knowing where these species will winter – with all the existing connections with the different breeding areas – is therefore a key factor in establishing the right kind of 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.’ This study combines what we know of the species’ migratory connectivity with what we know of their environmental habitat preferences.

“The results obtained help us understand not only how the three species migrate and behave in their wintering areas, but also how this migratory behaviour may have played a role in the evolutionary segregation of the three taxa,” said Raül Ramos, associate professor at the Department of Evolutionary Biology, Ecology, and Environmental Sciences of the Faculty of Biology.

“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.”

In his paper, Ramos has explained that 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.

It’s according to the paper’s first author, Virginia Morera Pujol that oversight of the critical importance that wintering areas play could lead to a worst case scenario for migratory species. 

“If protection measures provide for a single wintering area for a species with very low migratory connectivity, the benefit for the species will be minimal,” she explained. “In turn, disturbances in a specific wintering area of a species with high migratory connectivity could cause local extinction of the species in one of its breeding populations because all individuals in that particular population would be affected.”

The paper has warned that the wintering areas described have “high fishing pressure” which makes the stocks more vulnerable to by-catches, while other non-lethal disturbances have also been identified, including overfishing and a reduction in available food. These, the paper has suggested, could turn out to be indirect causes of population decline in the medium and long term.

“This is particularly critical for the Cape Verge Cory’s shearwater, a species endemic to the archipelago and which only breeds on these islands,” said Pujol. “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.”

Given the obstacles in place in accessing and observing oceanic birds for the study of their movements, this research paper has relied heavily on international collaboration as well as advancing technologies to track marine birdlife. 

“Thanks to the enormous volume of data contributed by different teams from all over the world, it has been possible to address the cost and logistics required for a study like this, putting the conservation and protection of seabirds with a wide geographical range at the centre of interest,” said the study’s authors.

The paper – titled Migratory Connectivity and Non-Breeding Habitat Segregation Across Biogeographical Scales in Closely Related Seabird Taxa – is published in the scientific journal Diversity and Distributions.

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