Great shearwater (Puffinus gravis)
|Also known as:||Greater shearwater|
|Size||Length: 43 - 51 cm (2)|
Wingspan: 100 - 118 cm (2)
|Weight||715 - 950 g (2)|
The great shearwater is classified as Least Concern (LC) on the IUCN Red List (1).
A large shearwater species of the Procellaridae family, and the biggest of the Puffinus genus, the great shearwater (Puffinus gravis) has a distinctive, dark blackish-brown cap, a contrasting white throat and a white collar on the back of the neck (3) (4) (5) (6). The upperparts are greyish-brown, with paler margins to the feathers, giving a scaled appearance (3) (4). The upper tail-coverts are white and the base of the tail is marked with a characteristic narrow white, horseshoe-shaped band (2) (3) (6) (7) (8) (9).
The underparts of the great shearwater are white, except for a variable, sometimes mottled, dusky brown patch on the belly, dark shoulder markings, and dark trailing edges and tips on the underwings (2) (3) (4) (5) (7) (10). The bill is dark grey and the legs and feet are pink (3) (4) (5) (9).
The great shearwater is particularly renowned for being one of only a few bird species to migrate from breeding grounds in the Southern Hemisphere to winter in the Northern Hemisphere(2). Shearwaters are named for the way in which they fly close to the water, with the wingtips almost touching, or ‘shearing’, the surface. The great shearwater has a particularly distinctive flight pattern, alternating between slow, powerful wing beats and long gliding periods with the narrow wings held stiff and straight (2) (6) (7) (8) (9).
The great shearwater has a piercing ‘eeyah’ cry, which is usually given when it rests in large groups on the water (7).
The great shearwater breeds in the South Atlantic on Nightingale and Inaccessible Islands in the Tristan da Cunha group, and on Gough Island (2) (3) (7) (8) (10) (11). Small numbers of the great shearwater may also breed on Kidney Island in the Falkland Islands (2) (8) (10) (11).
Outside of the breeding season, the great shearwater follows a circular migration route along the east coast of South America, north along the coast of the U.S., to the North Atlantic, where it winters along coastlines to the Arctic circle before returning south along the coast of northwest Africa (2) (12) (13) (14).
This species is an uncommon non-breeding resident in the Bahamas and off Puerto Rico (16).
A pelagic species, the great shearwater spends most of its time at sea, only coming to land to breed. It nests on remote volcanic islands, on areas of sloping ground among tussock grass or Phylica woodland where the soil is typically loose or peaty (3) (8) (10) (16).
During the non-breeding season, the great shearwater is found around the cooler waters of continental shelves, gathering in areas where ocean upwellings and strong surface currents concentrate prey (8).
The great shearwater feeds primarily on fish, squid and crustaceans, which it catches from the surface or by plunge-diving into the water (3) (7) (10) (11) (16). Species in the genus Puffinus are among the deepest diving members of the Procellariiformes (17). The great shearwater also feeds on fish offal, following in the wake of fishing boats and trawlers to scavenge for cast-offs and discarded bycatch (2) (3) (7) (16).
Breeding generally occurs in densely packed colonies numbering many thousands of pairs. The great shearwater returns to the colonies from late August or September (8) (14), and engages in courtship rituals where the breeding birds sit close together on the ground, softly biting each other’s necks and rumps to cement the pair bond (8). Mating begins in October or November, in burrows excavated in grass or woodland. A single, large white egg is laid in the nest chamber in mid-November, and is incubated for around 55 days. Both of the great shearwater adults tend the young, foraging by day and returning to the burrow at night. The young shearwater chick fledges in April, at around 84 days old, and is then abandoned by the adults, although it remains in the burrow until it is between 105 to 120 days old (2) (8) (10) (14). The adult great shearwater begins its migration in April and the juveniles follow in May (3) (8) (10) (16).
As a ground nesting species, the great shearwater is particularly vulnerable to predation by invasive species such as cats, rats and mice. On Gough Island, mice are a particularly severe threat, and in 2006 an estimated 700,000 house mice (Mus musculus) killed over 1 million seabird chicks of several species, including the great shearwater (8). Several thousand adults and around 50,000 chicks of the great shearwater are also harvested annually from Nightingale Island for food, at levels which are currently considered unsustainable (3) (16).
In addition, the great shearwater may face further threats, including oil spills, pollution, and mortality through collision with longline fishing gear (8).
There are no specific conservation measures currently targeted at the great shearwater. It is listed as a species of High Concern on the North American Waterbird Conservation Plan (2002) (18) due to apparent population declines in North American waters (8).
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- Bycatch: in the fishing industry, the part of the catch made up of non-target species.
- Continental shelf: a region of relatively shallow water, not usually deeper than 200 metres, surrounding each of the continents.
- Coverts: small feathers concealing the bases of larger flight feathers, usually on the wings or tail.
- Crustaceans: diverse group of arthropods (a phylum of animals with jointed limbs and a hard chitinous exoskeleton) characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.
- Genus: a category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
- Incubate: to keep eggs warm so that development is possible.
- Pelagic: in birds, applied to sea birds that come to land only to breed, and that spend the major part of their lives out at sea.
- Upwelling: the upward movement of cold, nutrient-rich water from the ocean depths, usually as a result of winds and currents.
IUCN Red List (March, 2011)
BirdLife International - Great shearwater (March, 2011)
- Blake, E. R. (1977) Manual of Neotropical Birds: Spheniscidae (Penguins) to Laridae (Gulls and Allies). University of Chicago Press, Chicago.
- Dunn, J. and Alderfer, J.K. (2006) National Geographic Field Guide to the Birds of North America. National Geographic Books, Washington.
Bird Guides - Great shearwater (March, 2011)
- MobileReference. (2008) The Illustrated Encyclopedia Of North American Birds: An Essential Guide To Birds Of North America. MobileReference, Boston.
Audubon - Great shearwater (March, 2011)
whatBird.com - Great shearwater (March, 2011)
Avibirds European Birdguide Online - Great shearwater (March, 2011)
New England Seabirds - Greater shearwater (March, 2011)
- Barbieri, E., Garcia, C.A.B., de Andrade Passos, E., Aragão, K.A.S. and do Patrocínio Hora Alves, J. (2007) Heavy metal concentration in tissues of Puffinus gravis sampled on the Brazilian coast. Revista Brasileira de Ornitologia, 15(1): 69-72.
World Register of Marine Species - Great shearwater (March, 2011)
Tristan da Cunha - Great shearwater migration project (March, 2011)
- Raffaele, H.A. (2003) Birds of the West Indies. Princeton University Press, Princeton, New Jersey.
Mongabay - Great shearwater (March, 2011)
- Ronconi, R.A., Ryan, P.G. and Ropert-Coudert, Y. (2010) Diving of Great Shearwaters (Puffinus gravis) in Cold and Warm Water Regions of the South Atlantic Ocean. PLoS One, 5(11): 1-7.
North American Waterbird Conservation Plan (March, 2011)