Justification This species has been downlisted to Vulnerable owing to the improving status of the population and habitat, in particular following the successful eradication of the last introduced predators (Pacific rat) on Little Barrier Island (where by far the largest numbers breed), leading to an increase in fledging success from 5% to 70%. This key step in turning the fortunes of the species followed the earlier eradication of cats from Little Barrier Island in 1980, and Weka from Codfish Island in the early 1980s. Although tiny numbers still occur on Great Barrier Island it may have been effectively extinct as a reproductively viable population for several decades.

Family/Sub-family Procellariidae

Species name author (Gray, 1843)

Taxonomic source(s) AOU checklist (1998 + supplements), Brooke (2004), Christidis and Boles (1994), SACC (2005 + updates), Sibley and Monroe (1990, 1993), Stotz et al. (1996), Turbott (1990)

Synonyms Pterodroma cooki Stotz et al. (1996), Pterodroma cooki Collar and Andrew (1988)

Identification 26 cm. Small, grey-and-white petrel. White forehead merging into grey crown. Pale grey crown, neck, back, uppertail-coverts. Darker grey wings showing "M" in flight. Tail slightly darker grey than back. Darker still on tips of central feathers. Outer feathers can be white. White underparts. White underwing with dark tip and dark line along leading edge, extending indistinctly from carpal joint towards body. Similar spp. Separated from most other small gadfly petrels by whiter underwing. Pycroft's Petrel P. pycrofti generally appears darker with darker crown and eye-patch. Outer tail feathers never as white as in some Cook's Petrels. Stejneger's Petrel P. longirostris has darker crown, nape, all dark grey tail. De Filippi's Petrel P. defilippiana has longer, thicker bill, longer tail.

Population estimate

Population trend

Range estimate (breeding/resident)

Country endemic?

1,258,000

increasing

320 km²

Yes

Range & population Pterodroma cookii is endemic to New Zealand, where it breeds on Little Barrier, Great Barrier and Codfish Islands. On Great Barrier, only 12 burrows have been found during the last 25 years; there may be fewer than 20 pairs⁶ and it is extinct as a reproductively viable population. On Codfish the population declined from c.20,000 pairs in the early 1900s almost to extinction before predators were removed in 1982; it is now increasing and was estimated at 5,000 breeding pairs in 2007^1,2,6,9. The population on Little Barrier is also likely to be increasing^2,4, and modelling and spatial analysis has suggested that as many as 286,000 pairs may breed on Little Barrier Island annually⁸. Birds migrate to the east Pacific Ocean, mainly between 34°S and 30°N¹.

Important Bird Areas Click here to view map showing IBAs where species is recorded and triggers any of the IBA criteria.

Ecology: It breeds in burrows on forested ridges and steep slopes between 300-700 m on Little Barrier and 4-350 m on Codfish; ideal breeding habitat is unmodified forest close to ridgetops with a low and open canopy and many large stems^2,7. It formerly bred in suitable habitat throughout New Zealand⁶. It feeds mainly on squid, crustaceans and small fish¹.

Threats On Little Barrier, introduced cats were a major predator of chicks and adults. Although cats were eradicated, the number of petrel burrows with chicks declined from 32% when both cats and rats were present to just 9% following cat eradication because the population of Rattus exulans (also a predator of petrel chicks) increased dramatically^1,4,5,7. On Great Barrier, the population is severely threatened by cats, black rat R. rattus and Pacific rat R. exulans. On Codfish, the population declined owing to severe predation by the introduced Weka Gallirallus australis².

Conservation measures underway Cats were eradicated from Little Barrier by 1980, and G. australis was eradicated from Codfish between 1980 and 1985⁴. R. exulans was succesfully eradicated from Little Barrier Island in 2004, increasing fledging success from 5% to 70%^7,9. An eradication operation took place in August 1998 on Codfish - the outcome of which is unknown³.

Conservation measures proposed Survey Codfish to locate new breeding burrows and colonies. Monitor breeding success and recruitment on Codfish, and map burrows at five-yearly intervals. Monitor status of population on Great Barrier: collect dead birds, tag and map active burrows, record locations of display areas. Implement appropriate pest control if a colony (more than five burrows) is found on Great Barrier. Reintroduce to mainland "islands" (areas of the mainland with intensive predator control)⁶.

References 1. Heather and Robertson (1997). 2. Marchant and Higgins (1990). 3. D. V. Merton in litt. (1998). 4. Taylor (2000). 5. G. A. Taylor in litt. (1999). 6. Imber et al (2003). 7. Rayner et al (2007). 8. Rayner (2006). 9. Anon (2005). 9. Rayner et al. (2008).

Text account compilers Phil Benstead (BirdLife International), Simon Mahood (BirdLife International), Rachel McClellan (BirdLife International), Andy Symes (BirdLife International), Helen Temple (BirdLife International)

Contributors Don Merton (Department of Conservation), Matt Rayner, Graeme A. Taylor (Department of Conservation), A. J. D. Tennyson

IUCN Red List evaluators Jeremy Bird (BirdLife International), Stuart Butchart (BirdLife International), Andy Symes (BirdLife International)

Recommended citation BirdLife International (2009) Species factsheet: Pterodroma cookii. Downloaded from http://www.birdlife.org on 10/2/2010

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

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