Cory's Shearwater

The Cory's shearwater (Calonectris borealis) is a majestic large seabird of the Procellariidae family. With a length of 45–56 cm and a wingspan stretching 112–126 cm, it presents a striking figure in flight. Its plumage is a blend of brownish-grey on the upperparts contrasting with the white underparts, and it sports a yellowish bill. This species is notably devoid of the great shearwater's brown belly patch, dark shoulder markings, and black cap.

Identification Tips

When observing Cory's shearwater, look for its sizeable profile and distinctive coloration. The lack of a dark cap and the presence of a yellowish bill are key features that distinguish it from similar species. In flight, its wings are bowed and angled slightly back, a posture that differs from the stiff, straight-winged flight of the great shearwater.

Habitat

Cory's shearwater is a bird of the open ocean. It breeds on rocky islands in the eastern Atlantic, favoring locations such as Madeira, the Azores, the Berlengas Archipelago in Portugal, and the Canary Islands in Spain.

Distribution

This species has a broad range, breeding in select Atlantic islands and dispersing widely across the ocean outside the breeding season. It is known to migrate as far north as the south-western coasts of Great Britain and Ireland before returning to the Mediterranean in February.

Behaviour

Cory's shearwater is a master of the air, gliding effortlessly over the sea with wings held in a characteristic bow. It is a social creature, often seen in large flocks, especially near fishing boats where it may engage in noisy disputes over food.

Song & Calls

While silent at sea, the breeding colonies of Cory's shearwater come alive at night with a cacophony of raucous cackling calls, a stark contrast to the bird's silent demeanor during the day.

Breeding

The breeding habits of Cory's shearwater involve nesting on open ground or among rocks, and occasionally in burrows. A single white egg is laid, and nocturnal visits to the nest help avoid predation by large gulls. The largest colony can be found in the Savage Islands of Madeira.

Diet and Feeding

An opportunistic feeder, Cory's shearwater dines on fish, molluscs, and offal. It is capable of diving to depths of 15 meters or more in pursuit of prey. Its presence behind fishing boats is a common sight, where it can be observed squabbling over scraps.

Conservation status

The Cory's shearwater is currently classified as Least Concern by the IUCN, indicating a stable population without immediate threats to its survival.

Similar Species

The Cape Verde shearwater (C. edwardsii) was once considered a subspecies but is now recognized as a separate species. It has a darker head, upperparts, and a slimmer, all-dark bill. Scopoli's shearwater was also part of the Cory's shearwater complex but is now a separate species, distinguishable by differences in mitochondrial DNA, morphology, and vocalization.