With a few, deep beats of its long wings, the Cory's Shearwater rides air currents just above ocean waves. The largest shearwater in North American waters, it patrols the warm, summer ocean of the Atlantic for squid and fish. Seldom seen from land, this seabird returns to rocky islands only to breed. Along with petrels and fulmars, shearwaters are called tubenoses, because a little pipe, fixed to the top of their bill, covers their nasal holes.
A large seabird, the Cory's Shearwater weighs about 1.8 pounds and measures 18 inches long with a 44-inch wingspan. The upper parts are mostly light brown. The outer wing is dark, as is the short tail. The underparts are whitish, and the underwing is white with dark edges and a dark "hand." An indistinct, dusky mask covers the eye and contrasts with the brown head. The stout, yellow bill is hooked and tipped with dark gray. The Cory's Shearwater has a distinct flight pattern: stiff, often bowed wings; infrequent, deep wing beats; and a steady, albatross-like glide.
Two distinct subspecies of Cory's Shearwater breed in separate locations. The Atlantic population breeds off the coasts of Portugal and northwestern Africa. Large colonies persist on the Azores, the Berlengas (Portugal), Canary, and Salvage Islands. The Mediterranean population breeds on rocky islands from the coast of Spain to Crete. The Cory's Shearwater winters off the southern and southeastern coasts of Africa, with smaller numbers into the southern Indian Ocean. In North American waters, this seabird appears in significant numbers from late May through August.
The Cory's Shearwater breeds on sparsely vegetated islands in temperate waters. This pelagic bird forages over warm, continental shelf waters (not more than about 2000 feet deep) and concentrates where water types mix, like the interface between the Gulf Stream and North American near-shore waters. These oceanic features bring food to the surface and host large mats of Sargassum, which also attract its prey.
A keen sense of smell leads the Cory's Shearwater to its prey. Skimming just above the ocean, it picks food from or dives just below the surface. It also snatches prey while sitting on the water. Many small fish are consumed: Atlantic saury, horse mackerel, boarfish, and trumpetfish. This seabird forages over groups of feeding dolphin, tuna, and seals, to take fish and to scavenge. Driven to the surface from all depths, small squid are an important part of the diet. A special organ just above the stomach stores fish oil as an energy reserve for the Cory's Shearwater.
Almost always returning to the same rocky islands, the Cory's Shearwater forms colonies with other seabirds. Apparently monogamous, pairs re-form bonds by sitting close and preening each other. Nest sites are usually reoccupied, and breeding is synchronized with neighbors, which change little year to year. This faithfulness may help defend against predators or help pairs form more quickly.
The nest is placed in a burrow or crevice. A single white egg is sometimes laid on top of small stones or shells, but often sits on the bare ground. Interestingly, older females lay larger eggs, which are more likely to survive. For 52-62 days, the pair takes turns incubating the egg in shifts that last an average of eight days. Like other shearwaters, the Cory's visits its nest mostly at night, and adults and young defend the nest by regurgitating noxious oil onto intruders. The chicks grow slowly. Adults provide care for up to 100 days, and often abandon their young before they fledge, as late as the beginning of November.
Migration patterns for the Cory's Shearwater are not completely understood. Spring migrants begin arriving at breeding colonies as early as March, with most arrivals in late April and early May. The Cory's Shearwater can be fairly common off the east coast of North America in the warmer months, and these birds probably represent a mixture of non-breeders and post-breeders that disperse westward. Departing North American waters in September and October, migrants begin to appear off South American and West African coasts in October and November.
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