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).

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).

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).