Great Shearwater
Great Shearwater
Ardenna gravis
At a Glance
A common seabird off our Atlantic Coast, seldom coming close to shore except during storms. Often forages in flocks. Commonly feeds around fishing boats, fighting over scraps and offal, seemingly fearless of humans. Although Great Shearwaters are often very numerous in North American waters, they nest only on a few islands in the South Atlantic.
All bird guide text and rangemaps adapted from by Kenn Kaufman漏 1996, used by permission of Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Category
Gull-like Birds, Shearwaters and Petrels
IUCN Status
Least Concern
Habitat
Open Ocean
Region
Alaska and The North, Eastern Canada, Florida, Mid Atlantic, New England, Southeast
Behavior
Flap/Glide, Swimming
Population
10.000.000
Range & Identification
Migration & Range Maps
Adults leave breeding islands in April and move north rapidly, mostly along western side of Atlantic, becoming common off east coast of North America in June. Spread eastward across North Atlantic during summer, and southward migration is on broad front during August. Nonbreeders remain in North Atlantic at least through November. Rare records off California presumably of birds that rounded tip of South America and went north in "wrong" ocean.
Description
18-20" (46-51 cm). Contrasting pattern with sharp black cap, dark gray-brown back set off by narrow whitish band across rump and usually across nape. White below with black marks under base of wing, blurry dark patch on belly.
Size
About the size of a Crow, About the size of a Mallard or Herring Gull
Color
Black, Brown, White
Wing Shape
Long, Narrow, Pointed, Tapered
Tail Shape
Pointed, Rounded, Wedge-shaped
Songs and Calls
Usually silent at sea, but birds resting on water have a low nasal, squealing call.
Call Pattern
Flat, Undulating
Call Type
Hoot, Odd, Raucous, Scream
Habitat
Open ocean. Favors cold waters at all seasons, moving rapidly across tropical zones during migration only. Tends to occur over colder waters than Cory's Shearwater. Perhaps most common over outer part of continental shelf, avoiding mid-ocean and areas near shore. Nests on hilly islands with soil suitable for nesting burrows.
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Behavior
Eggs
One. White. Incubation is probably by both sexes, estimated at 55 days.
Young
Both parents feed young, visiting at night. Age at first flight is reportedly about 84 days.
Feeding Behavior
Forages by plunging into water from the air, by diving from surface and swimming underwater, or by seizing items while swimming on the surface. Prey caught underwater is brought to surface and swallowed. May feed in association with whales and dolphins. Typically feeds by day but apparently also at dusk and at night.
Diet
Mostly fish and squid. Feeds mainly on small fish and squid that swim in schools near surface; also eats crustaceans, and scavenges offal from fishing boats.
Nesting
Breeds mainly on Gough Island and islands in Tristan da Cunha group in South Atlantic. Arrives at colonies in September, most eggs laid in November, most young leave colony in May. Activity at colony is mainly at night. Courtship display includes pair sitting close together on ground, calling loudly and nibbling at each others' nape feathers. Nest: Site is in burrow, sharply angled and about three feet long; sometimes in crevice among rocks. Nest chamber at end of burrow lined with grass.
Conservation
Conservation Status
Total population has been estimated at around 15 million. Could be vulnerable because of very limited breeding range; Tristan islanders harvest large numbers of adults and young every year from certain colonies.