Cory's Shearwater: where and when to see them

Cory's shearwater is a large Atlantic seabird closely associated with Portuguese island waters, including Madeira and the Azores. Long wings carry it in sweeping arcs above the waves, often with remarkably little flapping. It breeds in cavities and burrows on islands but ranges widely to feed and migrate. Modern taxonomy separates it from Scopoli's shearwater of the Mediterranean, so older accounts using Cory's shearwater broadly may describe more than one species.

Size

45–56 cm long

Weight

600–1,000 g

Lifespan

Not reliably established

Status

Least Concern

These shearwaters exploit wind above the sea, alternating low glides with higher banking turns. They may gather in offshore rafts before approaching breeding colonies after dark. Pairs generally maintain long-term bonds and share incubation of a single egg, followed by repeated feeding trips for the chick. Their noisy nighttime colony calls contrast with their usually quiet behaviour at sea, where they may associate with other feeding seabirds. Courtship displays and pair bonding are primarily conducted at the breeding colonies, often involving mutual preening. While at sea, they are highly pelagic, spending most of their lives far from land except during the breeding season.

• Pairs normally lay just one egg per breeding attempt.
• Its nasal tubes help support an excellent sense of smell.
• Young birds can be grounded by artificial lights during their first flights.
• Atlantic migrations can involve vast looping routes shaped by prevailing winds.

March to October broadly overlaps breeding-season presence around Portuguese Atlantic colonies. Late spring through early autumn usually offers practical coastal watching conditions, although passage varies by island and coastline. Winter movements take many birds farther south, reducing predictable observation near breeding areas. Peak numbers are observed during the post-breeding dispersal period, when juveniles and adults move through coastal waters before their southward migration. Early morning and late afternoon are often the most productive times for observing birds actively flying or rafting.

The species feeds over Atlantic shelf waters and the open ocean, often around productive fronts and island slopes. Breeding sites include rocky island crevices, burrows and sheltered cavities. Accessible headlands can overlook passing birds without requiring entry into sensitive colonies. The species shows a strong preference for oceanic islands and islets, providing isolation from terrestrial predators. These breeding colonies can host thousands of pairs, forming dense concentrations on suitable terrain.

Fish and squid are major foods, supplemented by crustaceans and sometimes fishery discards. Birds locate prey near the surface and may feed in groups where food concentrates. Adults transport partly digested meals and energy-rich stomach oil back to their single chick. They employ surface-seizing and shallow-plunging techniques to capture prey, often dipping their heads below the surface. Group feeding can involve dozens to hundreds of individuals, indicating cooperative foraging or attraction to abundant patches.

Common name

Cory's Shearwater

Scientific name

Calonectris borealis

Animal group

Birds

Size

45–56 cm long

Weight

600–1,000 g

Lifespan

Not reliably established

Status

Least Concern

Identification

Its robust yellow bill and mostly dark outer underwing distinguish it from smaller shearwaters, while Scopoli's typically shows more white extending into the underside of the outer primaries. Their overall brownish-grey upperparts contrast with white underparts, creating a distinctive 'two-toned' appearance in flight. The relatively long wings, often held slightly angled, contribute to their characteristic effortless gliding flight.