LC
Great Shearwater Ardenna gravis



Justification

Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.

Population justification
Brooke (2004) estimated the global population to number at least 15,000,000 individuals. A minimum of 5,000,000 pairs are thought to breed at Tristan da Cunha, and 600,000 to 3,000,000 pairs at Gough (Carboneras 1992d).

Trend justification
The population is suspected to be stable in the absence of evidence for any declines or substantial threats.

Distribution and population

This species breeds at three main sites: Nightingale and Inaccessible islands in the Tristan da Cunha group, and Gough Island, Tristan da Cunha (to UK) (Snow and Perrins 1998, Carboneras 1992d). Birds also breed in small numbers in the Falkland Islands (Malvinas), where the only confirmed site is Kidney Island (no more than 15 pairs recorded in 1987 (Woods 1988)), though there is a slight possibilty of breeding near Wineglass Hill, East Falkland, where one has been caught (Woods and Woods 1997).

Ecology

Adults begin a transequatorial migration in April, moving north-west to South America, up to Canada, past Greenland and onto the north-east Atlantic before returning south in November to the breeding islands (Carboneras 1992d, Harrison 1983). The species breeds on sloping ground, mainly in areas of tussock grass or Phylica woodland. It feeds mostly on fish, squid and fish offal (attending trawlers, sometimes in large numbers), and also on some crustaceans (Carboneras 1992d).

Threats

Several thousand adults and c.50,000 chicks are harvested every year from Nightingale Island by Tristan Islanders, which could lead to the collapse of the population without research into sustainable harvesting levels (Carboneras 1992d). Although there is no real evidence of threats to the tiny confirmed Falkland breeding population, predation by feral cats at Wineglass Hill would be a threat to any breeding there (R. Woods in litt. 1999).

Identification

47$cm. Large, distinctly capped shearwater, mainly of the Atlantic. Dark blackish brown cap and white hind-neck create capped appearance. Brown back, upperwing and rump; paler fringes to feathers produce scaled effect. White rear uppertail-coverts. Dark brown tail. White underparts except for variable brown belly patch (can be difficult to see). White underwing except for dark trailing edge and wingtip. Pink legs and feet but for black outer side to tarsus and outer toe. Dark grey bill. Similar spp. Cory's Shearwater Calonectris diomedea is less obviously capped and has paler bill plus more extensive dark area under the wing tip.

Acknowledgements

Text account compilers
Butchart, S., Ekstrom, J. & Newton, P.


Recommended citation
BirdLife International (2018) Species factsheet: Ardenna gravis. Downloaded from http://www.birdlife.org on 20/02/2018. Recommended citation for factsheets for more than one species: BirdLife International (2018) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 20/02/2018.