Scientific name: Puffinus gravis (O'Reilly, 1818)
Bird group: Shearwaters and Petrels
Field characters. Length 43-51 cm; wingspan 102-118 cm. Larger than Manx Shearwater; almost as large as Lesser Black-backed Gull. Dark brown-grey upperparts and white underparts; diagnostic dark brown cap is bordered by a pale collar; black bill (yellowish with black tip in Cory's Shearwater); dark marks on underwing and axillaries. Has pale horseshoe mark over the tail but this character is shared by some Cory's Shearwaters. Blackish-brown belly patch is sometimes hard to see at a distance.
Voice. Silent at sea. Nocturnal flight-call is a harsh guttural "kaa-ough".
Distribution. Breeds on S Atlantic Islands, migrates to N Atlantic along American continent; spreads east during July and August and then reaches W European coast.
Habitat. Cool to cold pelagic waters.
Food. Fish and cephalopods.
Eggs. Size 78 x 43 mm (70-89 x 44-52), weight 102 g.