Wednesday, 17 September 2014

Great shearwater

Ardenna gravis

Photo by Alejandro Torés (Seabirds Galicia)

Common name:
great shearwater (en); pardela-de-barrete (pt); puffin majeur (fr); pardela capirotada (es); großer sturmtaucher (de)

Order Procellariiformes
Family Procellariidae

This species only breeds on Nightingale Island, Inaccessible Island and Gough island in the Tristan da Cunha archipelago, and on Kidney Island in the Falklands. Outside the breeding season they migrate north to winter along the coasts of North America and Europe, as far north as the Arctic Circle.

These birds are 43-51 cm long and have a wingspan of 100-118 cm. They weigh 670-995 g.

The great shearwater is a pelagic species, spending most of their life in offshore and pelagic waters. They only come to land to breed, in remote volcanic islands, in areas of sloping ground among tussock grass or Phylica woodlands.

They feed in groups, hunting fishes such as mackerel and capelin, squids such as Illex illecebrosus, and crustaceans, either by catching prey from the surface or by plunge-diving. They also take fish offal from fishing boats.

Great shearwaters breed in October-April. They are monogamous and usually nest in dense colonies of up to many thousands of pairs. They excavate a burrow in the ground, where the female lays a single white eggs which is incubated by both parents for 53-57 days. The chick is fed by both parents and fledges 85-120 days after hatching.

IUCN status - LC (Least Concern)
This species has an extremely large range and the global population is estimated to be over 15 million individuals. The population is suspected to be stable in the absence of evidence for any declines or substantial threats. However, several thousand adults and  about 50.000 chicks are harvested every year in Tristan da Cunha and there is no research to validate whether these levels of harvesting are sustainable.

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