Cook's petrel  (Pterodroma cookii)

Cook's petrel breeds on only three small islands, making it very vulnerable to threats. Whilst there is a substantial population breeding on Little Barrier Island (of around 286,000 pairs (11)), the population on Codfish Island declined from 20,000 pairs in the early 1900s, to approximately 100 pairs in the mid 1980s, as a result of predation by the introduced weka (a small ground-dwelling rail) and the Pacific rat. Today this population has recovered to approximately 5,000 breeding pairs (12). The Great Barrier Island population is threatened by cats, dogs, wild pigs and rats, and only 12 active burrows have been found despite extensive searches over the last 25 years (13).

The most effective conservation measure for this species is control of introduced predators. Feral cats were eradicated from Little Barrier Island in 1980 following an intensive programme (14), and Pacific rats were eradicated from Little Barrier and Codfish Islands in 2004 and 1998, respectively (15). The weka, that used to prey on Cook's petrel on Codfish Island, was removed through selective culling and the relocation of birds to other islands. As a result of these actions, numbers of Cook's petrel on both islands are now increasing (12). However, the population on Great Barrier Island teeters on the edge of extinction, and requires immediate surveying and, if a colony is located, a programme to control introduced predators should be implemented (3) (12).