Cory's Shearwater

Fascinating facts about the Cory's Shearwater

• At up to 56 cm long with a 126 cm wingspan, this shearwater has long, bowed wings and flies with long glides, unlike the stiff, straight-winged flight of the similarly sized great shearwater.
• A single white egg is laid in an open scrape or shallow burrow, which the parents visit only after dark to avoid gull predators. Night-time nesting reduces the risk of egg loss, illustrating how timing can be as vital as camouflage for seabird survival.
• During the non-breeding season the birds travel as far north as the south-western coasts of Great Britain and Ireland, then turn back to the Mediterranean in February. Such a seasonal loop links distant marine ecosystems, highlighting the species’ role as a connector of Atlantic and Mediterranean food webs.
• Cory’s shearwaters can dive 15 m (about 49 ft) or deeper to chase fish, molluscs, and even ship offal, and they frequently follow fishing vessels, engaging in noisy squabbles over scraps. Their willingness to exploit human activity reveals a flexible foraging strategy that can both aid and endanger them depending on fishing practices.
• The largest known colony nests on the Savage Islands, a remote outpost of Madeira, demonstrating how a single isolated location can support massive numbers of birds. This concentration makes the islands a critical conservation hotspot, because any disturbance there could ripple through the species’ global population.

At a glance

About the Cory's Shearwater

Cory's shearwater (Calonectris borealis) is a striking seabird, measuring 45–56 cm in length with a wingspan of 112–126 cm. Its plumage is a seamless blend of brownish-grey upperparts and crisp white underparts, capped by a distinctive yellowish bill that sets it apart from the great shearwater’s darker facial markings. When it soars over the Atlantic, the bird’s wings are bowed and angled back, producing long, graceful glides that contrast with the stiff, straight-winged flight of its great-shearwater cousin. Breeding colonies dot the volcanic islands of Madeira, the Azores, the Berlengas Archipelago, and the Canary Islands, where they nest on open ground, among rocks, or in burrows visited only under the cover of night to evade gull predation. After the breeding season, these birds embark on vast migrations, reaching as far north as the southwestern coasts of Great Britain and Ireland before returning to the Mediterranean in February. Their diet is a versatile mix of fish, molluscs, and even offal, and they are adept divers, plunging 15 m or more to chase prey, often trailing fishing vessels in noisy, competitive squabbles. A surprising trait is their nocturnal vocal chorus: while silent at sea, breeding colonies erupt at night with raucous cackling calls, a soundscape that can be heard echoing across the cliffs and open ground where the largest colony thrives on the Savage Islands of Madeira.

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