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.
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 1992).
The population is suspected to be stable in the absence of evidence for any declines or substantial threats.
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) (Carboneras 1992, Snow and Perrins 1998). 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 possibility of breeding near Wineglass Hill, East Falkland, where one individual has been caught (Woods and Woods 1997).
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 (Harrison 1983, Carboneras 1992). 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 crustaceans (Carboneras 1992).
Great Shearwaters are subject to one of the highest levels of bycatch in the Atlantic Ocean (ICES 2013), with considerable mortality detected in the Grand Sol fishery but recent monitoring of this area is poor. Bycatch also occurs off the coast of the northeast Atlantic (Hatch et al. 2016). Several thousand adults and c.50,000 chicks are harvested every year from Nightingale Island by Tristan da Cunha islanders, which could lead to the collapse of the population without knowledge of sustainable harvesting levels (Carboneras 1992).
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.
Text account compilers
Ekstrom, J., Fjagesund, T., Hermes, C., Butchart, S., Martin, R., Newton, P., Stuart, A.
BirdLife International (2021) Species factsheet: Ardenna gravis. Downloaded from http://www.birdlife.org on 28/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 28/10/2021.