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). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to 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.
Taylor (2000) estimated the global population as 200,000 to 300,000 breeding pairs, equivalent to 400,000-600,000 mature individuals or approximately 600,000-900,000 individuals.
The population is suspected to be in decline owing to predation by invasive species and unsustainable levels of exploitation.
Pterodroma gouldi breeds in many colonies around the northern part of North Island, New Zealand. Outside the breeding season it disperses in the subtropical southwest Pacific Ocean, mainly between 25 and 50 degrees south, although some birds will stray into the Antarctic zone (del Hoyo et al. 1992, Brooke 2004).
This marine species is highly pelagic and has a widespread, but sparse, distribution at sea. It feeds mostly on squid, with some fish and crustaceans, most of which it obtains by dipping and surface-seizing. Documented feeding events have taken place at night, and the prevalence of bioluminescent species in the diet suggest that this is the method by which the birds locate their prey (Imber 1973, Harper 1987). It can occasionally be seen following cetaceans and will associate with other Procellariiformes. Breeding occurs in winter, with birds returning to colonies in February (Brooke 2004). Nesting is in loose colonies on oceanic islands on ridges, slopes or flat ground, with birds using (and probably excavating) burrows c.1.5 m long. Breeding usually occurs below 400 m. Fledging occurs in late December (Brooke 2004).
Invasive mammalian predators are the main threat faced by the Grey-faced Petrel. Cats, Polynesian Rats, Brown Rats, House Rats, stoats and pigs are all thought to cause population declines through nest depredation causing a loss of reproductive success, with cats also taking adults. Eradication efforts have taken place to reduce the population of both cats and Polynesian Rats. The removal of each species from breeding islands resulted in an increase in the population of Grey-faced Petrels (Greene et al. 2015). Cats remain on one breeding island and are present throughout the mainland distribution outside of fenced areas, while Polynesian Rats remain in some areas of its range. Brown Rats and House Rats remain on nine and fourteen breeding islands, respectively. The species is still legally harvested on some offshore islands in the Bay of Plenty and Hauraki Gulf; however, attempts have been made to ensure that current harvest is sustainable (Greene et al. 2015).
42-45 cm. A large, all-dark Pterodroma with a stout black bill and whitish grey face. Long wings give a light, buoyant flight and the plumage recalls Black-footed Albatross.
Text account compilers
Calvert, R., Ekstrom, J., Butchart, S., Fjagesund, T., Hermes, C., Martin, R., Stuart, A., Symes, A., Taylor, J.
BirdLife International (2021) Species factsheet: Pterodroma gouldi. Downloaded from http://www.birdlife.org on 24/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 24/10/2021.