Audubon's Shearwater skims close to the sea surface, alternately gliding and flapping with rapid wingbeats. Good sightings are difficult, as these small shearwaters always seem to be on the move, either individually or in flocks numbering in the hundreds. Around dusk, birds wait offshore for darkness to fall, before returning to their remote island nesting burrows. At night these breeding colonies are noisy with their twittering and mewing calls.
Audubon's Shearwaters average 12 inches in length, with a wingspan of 27 inches, and weigh six ounces. While there is much geographical variation between the more than 10 recognized subspecies, this small shearwater is generally dark brown above and pale below, with pinkish legs, and a dark, hooked bill. Sexes are similar, and distinguishable from other shearwaters by a white spot in front of the eye and dark under-tail coverts that extend to the tip of the long tail, which projects beyond the tips of the bird's relatively short, broad wings. The Audubon Shearwater's face lacks the white crescent behind the eye, and the under-wings have a wider dark margin than the very similar Manx Shearwater.
Audubon's Shearwaters are widespread in tropical waters throughout the Atlantic, Pacific, and Indian Oceans. In North America, they are found over the warm waters off the southeastern U.S. coast, and can usually be seen from June through early September south of Cape Cod.
Audubon's Shearwaters come ashore only to breed. These pelagic seabirds primarily occur over warm water, whereas the similar Manx Shearwater prefers cold water. Audubon's Shearwaters follow the tropical Gulf Stream current north. Colonies nest on isolated islands, utilizing rock crevices and vegetation clumps along rocky coasts as well as wooded inland areas.
Audubon's Shearwaters forage by seizing prey near the surface, or by diving into the water from low flight or from the surface, then utilizing their ability to row underwater with their wings. They feed on small crustaceans, squid, and fish, including many sardines. Adults do not seem to follow fishing boats, as related species do.
Audubon's Shearwaters arrive at their nocturnally active island colonies three months before egg-laying. Mated pairs spend a significant amount of time together at their nest site performing courtship displays such as rubbing their bills together, and calling loudly. Both parents prepare the nest, which may lie within a natural rock crevice, an underground burrow, or beneath dense vegetation. The single white egg is incubated by both parents for 51 days. Once hatched, both parents visit and feed the chick by night for another 70 days. Three to five days after the last feeding, the chick leaves the nest at night, climbs to a high point nearby, and takes its first flight into the sea. Once fledged, the chick will take eight years to reach breeding age, and like other shearwaters, may be long lived.
Audubon's Shearwaters move north within the Gulf Stream in late summer and fall; some move into the Gulf of Mexico. The higher the water temperature, the further north they may go, however they tend not to migrate nearly as far as other related shearwaters.
Alsop, Fred J. Birds of the Mid-Atlantic. DK Publishing, Inc., New York, 2002
Kaufman, Kenn. Lives of North American Birds. Houghton Mifflin Company, New York, 1996
Sibley, David Allen. The Sibley Guide to Birds. Alfred A. Knopf, Inc., New York, 2000
