Courtesy Kenn Kaufman
Although this shearwater breeds locally in Newfoundland and rarely south to Massachusetts, most of the population breeds in the British Isles. The primary breeding range includes the Westmann Islands in Iceland, the Faeroe Islands, Great Britain, Ireland, France, the Azores, Madeira, and the Canary Islands. Middle Lawn Island in Newfoundland contains the largest North American breeding colony.
Off North America, Manx Shearwaters generally occur over cooler water. They often feed close to shore, and nest mostly on small islands near the mainland. While the Manx prefers cold water, the very similar Audubon's Shearwater prefers warm water.
The Manx Shearwater forages by diving into water from low flight, making shallow dives from the surface, or seizing prey at the surface, or just below, then utilizing its ability to swim underwater. It feeds on a variety of common small fish, including herrings, sardines, and sand lance. Squid and crustaceans are also consumed. Adults seem to be attracted to small fishing boats. They may forage as far as 600 miles from their nesting grounds, returning at night.
The birds nest in dense, nocturnally active island colonies. Five year old Manx Shearwaters may begin breeding, and typically mate for life. The pair digs a burrow up to six feet in length, which they may reuse the following year. The nest chamber at the end of the burrow is lined with plant material. The pair spends significant amounts of time in the nest for several weeks before the single white egg is laid. Both parents incubate the egg for up to two months, and feed the chick for another two months, before finally abandoning it. The chick leaves the nest a little over a week later, heading off to sea alone.
The breeding season off northeastern North America lasts from May to October. Many shearwaters begin to move north in early spring. European colonies tend to winter off the east coast of South America. Banding studies have shown that British breeders typically winter in the seas off Brazil, although some individuals may wander further afield. There is evidence of increasing numbers wintering in the Magellan Straits.