VU
Cook's Petrel Pterodroma cookii



Justification

Justification of Red List Category
There have been rapid declines in the past, but the status of the species has improved, in particular following the successful eradication of the last introduced predators (Pacific rat Rattus exulans) 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 Gallirallus australis from Codfish Island in the early 1980s. The species is still restricted to a very small number of breeding locations, and if invasives should become established again on Little Barrier Island, extremely rapid population declines could ensue. Therefore, the species qualifies as Vulnerable.

Population justification
M. Rayner (in litt. 2012) estimates over 650,000 mature individuals on Little Barrier in 2007 and c.15,000 mature individuals on the Cod fish Islands in 2008, thus the total population estimate is rounded to c.670,000 mature individuals.

Trend justification
The population has suffered rapid declines in the past owing to the effects of introduced predators; however, thanks to conservation action and invasive species eradications it is now estimated to be increasing.

Distribution and population

Pterodroma cookii is endemic to New Zealand, where it breeds on Little Barrier, Great Barrier and Codfish Islands. Birds migrate to the eastern Pacific Ocean, mainly between 34°S and 30°N (Heather and Robertson 1997) although vagrants do wander as far north as the Gulf of Alaska and south of the Aleutians (Howell 2012). On Great Barrier, only 12 burrows have been found during the last 25 years; there may be fewer than 20 pairs (Imber et al. 2003) and it is extinct as a reproductively viable population, probably owing largely to the presence of rats Rattus spp. (M. Rayner in litt. 2012). 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 (Marchant and Higgins 1990, Heather and Robertson 1997, Imber et al 2003, Rayner et al. 2008), and in 2012 was thought to number c.5,000-6,000 breeding pairs (M. Rayner in litt. 2012). The population on Little Barrier is also likely to be increasing (Marchant and Higgins 1990, Taylor 2000), and modelling and spatial analysis has suggested that as many as 286,000 pairs may breed on the island annually (Rayner 2007b); six times the number previously suggested (Anon. 2007). Little Barrier/Hauturu Island supports 98% of the world population, with the remainder breeding on Codfish/Whenua Hau Island, off Stewart Island.

In 2010, 50 chicks were translocated from Little Barrier to Hawke’s Bay peninsula, south of Cape Kidnappers (Fallwell 2010). The project aims to translocate 350 chicks to build up the colony, following the fencing of a 2.5 ha site against mice and other predators (Fallwell 2010). Behavioural, morphological and genetic analyses has produced evidence of a distinct population genetic structure (Rayner et al. 2010), and a recent study of year-round movements indicates two separate migration routes over historic timescales, with birds at Little Barrier migrating to the northern Pacific Ocean and birds at the Codfish Islands migrating to the Humboldt Current (Rayner et al. 2011). These data imply that the two populations may be best treated as different subspecies and represent separate management units (M. Rayner in litt. 2012).


Ecology

It breeds in burrows on forested ridges and steep slopes at 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 (Marchant and Higgins 1990, Rayner et al 2007a). It formerly bred in suitable habitat throughout New Zealand (Imber et al 2003). It feeds mainly on squid, crustaceans and small fish (Heather and Robertson 1997).

Threats

Those birds on Great Barrier Island are at risk from predation from multiple invasive species, with cats, Weka, and Polynesian and Black Rats present (Ogden and Gilbert 2009), however, only 20 pairs still nest on this island. The Weka is also known to have decreased the population on Codfish Island (Marchant and Higgins 1990).

Conservation actions

Conservation Actions Underway
Cats were eradicated from Little Barrier by 1980, and Weka was eradicated from Codfish between 1980 and 1985 (Taylor 2000). Pacific Rat was successfully eradicated from Little Barrier Island in 2004, increasing fledging success from 5% to 70% (Rayner et al. 2007a, 2008). An eradication operation took place in 1998 on Codfish (D. V. Merton in litt. 1998). Translocation of chicks from Little Barrier to another potential nest site, Cape Sanctuary in Hawke’s Bay peninsula, is on-going (M. Rayner in litt. 2012). Chicks have been transferred at 50-60 days of age, 20 days before fledging, so that they have time to identify with their new location without needing prolonged feeding (Fallwell 2010). In early 2012, c.250 had been moved during three years (M. Rayner in litt. 2012).

Conservation Actions 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 the status of the population on Great Barrier: collect dead birds, tag and map active burrows, and 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) (Imber et al 2003).

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.

Acknowledgements

Text account compilers
Stuart, A., Symes, A., Taylor, J., Temple, H., Fjagesund, T., Anderson, O., Hermes, C., Benstead, P., Mahood, S., Martin, R., McClellan, R., Moreno, R.

Contributors
Tennyson, A., Merton, D., Taylor, G.A., Rayner, M., Morgan, K.


Recommended citation
BirdLife International (2022) Species factsheet: Pterodroma cookii. Downloaded from http://www.birdlife.org on 27/11/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 27/11/2022.