Greater shearwaters are a marine species distributed throughout the region of the Atlantic ocean. Puffinus gravis breed in the far south Atlantic, mainly on the islands of the Tristan da Cunha group, the Falkland Islands, and Gough Island. P. gravis then migrates to the North Atlantic during the winter, reaching noth-east Canada and sometimes reaching as far north as Greenland. Migration to the breeding grounds involves a flight east, past Britain and Iberia, than turning south to reach their Southern Hemisphere breeding grounds.

(del Hoyo, Elliot, and Sargatal 1992; Farrand 1985; Gooders 1978)

Biogeographic Regions: oceanic islands (Native ); atlantic ocean (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Non-breeding

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Non-breeding

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Breeds in southern Atlantic Ocean on Tristan da Cunha, Gough Island, and in Falkland Islands (Croxall et al. 1984). Ranges at sea throughout Atlantic Ocean from Greenland and Iceland to Tierra del Fuego and South Africa.

Puffinus gravis is a large shearwater species, 43-51cm in length, with a wingspan of 100-118cm. Colouring is unique with a combination of pale underparts with a poorly defined dark patch on the belly. White bands of plumage occur across the uppertail-coverts and also across the hindneck, emphasizing the Greater Shearwaters strongly capped appearance. Upperparts are dark gray-brown to black with light feather edgings to give a scaled appearance. Flight feathers have black upper- and undersurfaces. The tubenosed bill is long, thin, and black. The legs are pink to grey with webbed feet, and eyes are brown. Chicks have bluish-grey down and juveniles are similar to adults but greyer with paler fringes to feathers to give less scaled appearance. There is no sexual dimorphism in terms of size or colour between males and females.

(Campbell 1974; del Hoyo, Elliot, and Sargatal 1992; Farrand 1985; Gooders 1978)

Range mass: 715 to 950 g.

Length: 48 cm

Weight: 849 grams

• Terrestrial
• Marine

P. gravis is a marine, pelagic bird species, frequenting cool offshore and pelagic waters, and breeding on sloping ground, mainly in grassland or woodland areas (del Hoyo, Elliot, and Sargatal 1992; Gooders 1978)

Comments: Pelagic. Nests in burrows on oceanic islands.

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

Migrates north in western Atlantic in northern spring and summer (mainly May-September off U.S. coast).

Greater Shearwaters feed in groups where aggressive intraspecific feeding competition is evident through lashing with bills and wings. They eat mostly fish and squid, with occasional feeding on crustaceans, fish entrails, and other refuse discarded by fishing vessels. They hunt by plunge-diving from heights of 6-10m or taking prey from surface seizing or pursuit diving.

Surface-seizing consists of the 'walking on water' that is usually associated with Storm Petrels. Without entirely folding its wings, a Greater Shearwater lands on the water surface with its feet, balances with its wings, and "walks" forward over the water as it picks up food from near the surface.

Plunge-diving involves striking the water surface from heights of 6-10 m with belly and feet and then instantly lowering the head under the water surface to lead into a smooth submersion. Occasionally, a Greater Shearwater might briefly halt 0.5 m above the water surface, spread its feet, then plunge headfirst underneath the water. After the dive, the bird bursts out of the water and almost directly into flight.

(Brown, Bourne, and Wahle 1978; del Hoyo, Elliot, and Sargatal 1992; Gooders 1978)

Comments: Follows and catches surface-feeding fishes, also squids, crustaceans, and small fishes such as sand launces; dives under surface for fishes and rises into air to swallow. Also eats offal from fishing boats and apparently whale feces.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 1 - 20

Comments: Breeds at only four sites.

>1,000,000 individuals

Comments: More than 5 million pairs nest on Tristan da Cunha, and between 600,000 and 3 million pairs nest on Gough Island (del Hoyo et al. 1992).

Comments: When nesting, parents at sea most of day. Many birds over land at sunset, then come to ground. Night activity peaks at about 9 p.m. and 3:30 a.m. Asleep on ground from about midnight on. See Palmer (1962).

Average lifespan

Status: wild: 85 months.

The breeding season commences in October and often lasts until December. Breeding takes place in the Southern Hemisphere and is restricted to the far south oceanic islands: Tristan da Cunha group, Falkland Island, and Gough Island. Puffinus gravis is a colonial nester, nesting in burrows or crevices among boulders along hilly island shores. The female produces a single, white, oval, and slightly pointed egg. The egg is incubated for 53-57 days, and an altricial offspring is then hatched. Both male and female care for young. Offspring become independent of their parents at about 105 days. (del Hoyo, Elliot, and Sargatal 1992; Gooders 1978)

Average laying date is 11 Novenber. Clutch size is 1. Incubation lasts about 55 days. Young are tended by both parents, first fly at about 84 days, depart at about 105 days. Parents depart in April while young still in burrows. Average of 1.6 nesting burrows/sq yd (Palmer 1962).

Greater Shearwaters are not globally threatened. They are abundant with enormous total populations of a minimum 5 million breeding pairs on Tristan da Cunha, 600,000 to 3 million pairs on Gough Island, and small numbers on Falkland Islands. Their breeding range is restricted with only 4 sites known. Where the problem lies is with exploitation by Tristan islanders. Each year, a few thousand adults, and 50,000 chicks are taken. This could lead to a population collapse unless a quota system is established to allow for rational exploitation. More research is required in this area, as well as in the areas of the impact of harvesting on Greater Shearwaters, and the importance of other causes of mortality and population dynamics, in order to determine the maximum sustainable levels of exploitation. Another issue to be addressed is that of the occasional Greater Shearwater that is snared by fishermen's baited hooks.

Very little research has been done, but is required to ensure the maintenance of healthy populations of Puffinus gravis worldwide.

(del Hoyo, Elliot, and Sargatal 1992)

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N5N - Secure

United States

Rounded National Status Rank: N5N - Secure

Rounded Global Status Rank: G5 - Secure

Comments: Vulnerable because of restricted breeding distribution. A few thousand adults and about 50,000 chicks are harvested each year on Tristan da Cunha (del Hoyo et al. 1992).

In the past, Greater Shearwaters had been used to provide food and bait for seamen, but this practice has long since been discarded and aside from the occasional contact with fishermen, and Tristan islanders, P. gravis has mostly no contact with humans.

 (del Hoyo, Elliot, and Sargatal 1992; Cassidy 1990)