The Cory's Shearwater (Calonectris borealis) is a large seabird perfectly adapted to a life on the high seas. It only comes ashore to breed, establishing colonies on islands and coastal cliffs in the Atlantic. Nicknamed the "ghost of the oceans," it is famous for its nocturnal habits at nesting sites, where its eerie, wailing calls echo in the darkness.
This is the largest shearwater in the North Atlantic, significantly bigger than its smaller relative, the Manx Shearwater. Its identification is based on several key features:
By the Les-Oiseaux.com team, published on July 17, 2025
My advice: To experience the Cory's Shearwater, you have to think like one: stick to the sea or the night. The best way to see one is on a pelagic (offshore) birding trip, where you might also spot other impressive seabirds like the Northern Gannet, especially in late summer. But for the most magical moment, visit a colony (in the Azores or Madeira, for example) as night falls.
Find a safe listening spot and wait in silence. Hearing the first hoarse, spectral calls rising from the sea, then seeing these large shadows pass silently overhead to reach their nests, is an unforgettable experience. It's then that you understand why sailors gave them mysterious names. It's not just a bird; it's a voice of the ocean itself.
Cory's Shearwater is silent at sea but extremely vocal on land. It only visits its colonies at night, a behavior shared with the much smaller Storm Petrel, likely to protect itself from predators. It is then that it emits hoarse, prolonged, and almost ghoulish calls, often described as wails or crazed laughter. These vocalizations, which differ between males and females, play a crucial role in communication within the dense, dark colonies.
Cory's Shearwater was long considered a subspecies of the Scopoli's Shearwater (*Calonectris diomedea*), which breeds in the Mediterranean. Distinguishing them at sea is a classic birdwatching challenge. Here are the main clues to tell them apart:
Tip: Without a good view of the underwing, identification is very difficult. The location of the sighting is often the best clue: a large shearwater of this type seen in the Mediterranean is most likely a Scopoli's.
The Cory's Shearwater is a pelagic bird that spends most of its life on the open ocean. Its breeding areas are restricted to inaccessible islands and coastal cliffs in the North Atlantic, particularly in the Azores, Madeira, and the Canary Islands. After breeding, it undertakes a long trans-equatorial migration to spend the non-breeding season in the South Atlantic, off the coasts of South America and Southern Africa.
The map below illustrates the range of the Cory's Shearwater. The breeding areas (in orange) are highly localized, contrasting with the vast oceanic expanses it travels for the rest of the year.
Its diet consists mainly of small fish, squid, and crustaceans. It is a surface feeder that rarely dives deep. It often hunts at night when its prey moves closer to the surface. It is also known to follow pods of tuna and cetaceans, feeding on the fish they drive upwards, and will readily follow fishing boats for discarded bycatch.
The breeding season begins in the spring. Cory's Shearwaters are colonial and monogamous, with pairs often remaining faithful to the same partner and nest site year after year. The nest is a simple cavity in a burrow, rock crevice, or cave, which protects it from predators and heat. The female lays a single white egg, which both parents incubate in turns for about 54 days. The chick is fed by both adults, exclusively at night, and will fledge after about 90 days.
Although its populations are large, Cory's Shearwater faces several threats, including predation at colonies by introduced species (rats, cats), light pollution that disorients fledglings on their first flight, and accidental capture in fishing gear like longlines.
It is a remarkably long-lived bird, capable of living for more than 20 years. It reaches sexual maturity late, with the first breeding attempt often occurring between 5 and 13 years of age.
The name of their family, Procellariidae, comes from the Latin word "procella," which means storm. These birds are indeed remarkably at ease in strong wind conditions, which they skillfully use to travel immense distances at sea with minimal effort, seemingly playing with the waves and wind.