Cory’s shearwater (Calonectris borealis) is an elusive species of nocturnal seabird that nests in underground burrows and on remote islands in the Mediterranean and eastern Atlantic.
During their breeding season, the seabirds remain close to the colony to feed and care for their chicks. However, once the chicks are independent, the adults migrate thousands of kilometers across the ocean to warmer climates to feed during the winter. Some individuals return to the same winter foraging sites each year, yet others demonstrate the extraordinary ability to shift their wintering destinations widely from year to year.
Potential threats and stressors include introduced predators eating their chicks, the risk of mistaking massive amounts of plastic debris for food, encounters with coastal and offshore fisheries, artificial light disorienting fledglings, contending with pollution from highly trafficked shipping routes, and a changing climate. As their migratory routes overlap with areas of strong interest for offshore wind energy development and those leased for deep-sea mining exploration, those interactions are only likely to increase.
This is especially true during the three to four months of the year when they leave their nesting grounds and travel through the Exclusive Economic Zones of more than 30 countries and vast areas beyond national jurisdiction (ABNJ) in the north and south Atlantic to forage. For example, a portion of the population winters near the Rio Grande Rise, a cobalt-rich ocean ridge off the coast of Brazil. This area may soon be mined as the demand for rechargeable cell phone and hybrid or electric car batteries increases, (which require cobalt to make) presenting yet another environmental challenge for the species.
Cory’s shearwaters are not currently threatened. However, the potential cumulative impact of these wide-ranging stressors along with these seabirds’ long distance and variable post-breeding movements, present a good example of the need for coordinated management across sectors and jurisdictions to incorporate migratory connectivity into conservation and sustainable use efforts.
Hatched blue areas demonstrate the distribution of Cory’s shearwaters, based on a 90% utilization distribution. Exclusive Economic Zones that Cory’s shearwaters pass through during each stage of their annual cycle are highlighted in light red. Breeding colonies where birds were tagged are represented by blue plus signs: Berlengas (n=23) and Selvagens(n=103).
Breeding Season (~April to October)
During the breeding season, Cory’s shearwaters move through the waters of many European and African countries to forage and find food for their chicks.
Outbound Migration and Wintering Sites
In November and December, Cory’s shearwaters commence a long migration to their wintering areas in waters off South America and southern Africa.
Return Migration from Wintering Sites to Colonies
Following dominant wind patterns, Cory’s shearwaters move back across the Atlantic to their nesting colonies, with some birds looping through the northwest Atlantic along the way.
Data obtained with permission from BirdLife International Seabird Tracking Database | Tracking Ocean Wanderers. http://www.seabirdtracking.org/. Accessed Jan 2018