CORY’S SHEARWATER Calonectris diomedea

CORY’S SHEARWATER Calonectris diomedea

Cape Verde Shearwater (C. d. edwardsii)
L 41–46 cm, WS 95–125 cm.

IDENTIFICATION 

Large, heavily built shearwater, similar in size to Great. Flight action often seems lazy, yet in fact is often swift. Several deep but rather loose wingbeats (less stiff than other shearwaters) are followed by a long, low glide that is sometimes banking or circling. Typically holds wings slightly pressed forward and gently flexed, with a slight bow. In windier conditions rises in long, high sweeping arcs and will even soar at times. Frequently follows ships and scavenges. Often forms large rafts. Distinguished from Great by lack of capped appearance (mouse-brown head merges slowly into whitish throat and foreneck), pale yellowish bill with quite conspicuous dark subterminal area (but not race edwardsii, which has alldark bill), lack of dark patch on belly (but this not always present on Great), lack of dark markings across underwing coverts, distinctly more extensive black tip to underwing, and longer-, looser-winged, heavierheaded appearance. Many Cory’s lack the narrow white band across uppertail coverts shown by Great, but some Cory’s do show a narrow, indistinct white band and contrastingly dark tail can create illusion of pale band even when none exists. 

Coloration quite close to Yelkouan of race mauretanicus (‘Balearic Shearwater’); distinguished by larger, heavier appearance, rather ‘scaly’ grey-brown upperparts (often with contrastingly darker diagonal band across wing coverts), looser flight, paler head (with darker mask), thicker, mainly pale bill (except edwardsii) and much whiter underwing and underbody (including vent). 

Confusion also possible at long range with Northern Fulmar, but latter has shorter, stockier head and body, shorter, thicker bill, greyer and generally paler-looking upperparts, shorter wings and stiffer wing action and, in light morph, all-white head (but beware intermediates with grey crown and nape). See also Fea’s and Zino’s Petrels. Bleached and worn Cory’s can look very pale brown above.

VOICE 

On breeding grounds main call is a harsh, snoring, repeated wail, ‘keeowwrrah, keeowwrrah’ (with slight variations in each race). Silent at sea. 

TAXONOMY 

Form edwardsii is probably best treated as a separate species, Cape Verde Shearwater. 

GEOGRAPHICAL  VARIATION 

Quite marked. 3 races (borealis and edwardsii illustrated). Cape Verde Is race edwardsii about 10% smaller than northern races and more slightly built: somewhat darker brown neck and mantle, producing greater contrast with whitish underparts, and has particularly dark sooty brown hood contrasting with paler hindneck and whitish chin and throat; bill proportionately more slender, and greyishhorn with blackish subterminal area (looks rather uniform dingy grey at sea). Of the northern races, borealis (breeds Atlantic) is slightly larger and darker than nominate race (breeds Mediterranean) but probably inseparable in the field.

STATUS/HABITAT 

Fairly common. (Map note: in summer marine range extends north to SW Ireland and approaches to English Channel, and throughout Mediterranean as far as Sea of Marmara. Even visits Gulf of Aqaba. Some may remain around Cape Verde Is all year, but otherwise vacates region to winter in S Atlantic. Breeding areas seemingly mapped for mainland coasts in fact refer to nearby offshore islands. May breed outside mapped areas among Aegean Is and on Islas Chafarinas off Morocco.) Breeds in holes and crevices on cliffs, rocky slopes and (where undisturbed) even gently sloping ground, sometimes well inland. Pelagic away from breeding colonies, but regularly seen quite close inshore.