Cook’s petrel  (Pterodroma cookii)

Classified as Vulnerable (VU) on the IUCN Red List (1).

Cook’s petrel, named in honour of the formidable explorer Captain James Cook, is one of the smallest petrels, a group of oceanic birds that return to land only to breed. It has pale grey plumage on its crown and upperparts, and a white forehead, cheeks and underparts. A dark grey ‘M’ shape can be seen across the top of the wings when extended in flight, and underneath the wings appear white with a dark tip and a dark line along the leading edge (2) (3). The bill is long and black with tubular nostrils positioned on either side. This is a feature unique to the order Procellariiformes, which enables these birds to have an exceptionally acute sense of smell, used to locate food and nest sites in the dark (4). The name petrel comes from the Latin petrellus, which literally means ‘Little Peter’, after the Apostle who walked on water with Christ, and refers to the way they patter on, or hover just above, the oceans surface (5). Its call is a rather nasal kek-kek-kek, heard at night as it flies over land (6).

Cook’s petrel breeds only in New Zealand, on Little Barrier, Great Barrier and Codfish Islands. Outside of the breeding season they migrate to the Pacific coast of South America, and across the equator to the east Pacific Ocean, where they are generally found between 34°S and 30°N (2) (3).

A marine and highly pelagic bird, generally found over temperate and subtropical waters. It rarely occurs near land except when breeding on offshore islands, on forested ridges and steep slopes, between 300 and 700 meters above sea level (2) (7).

The breeding season of Cook’s petrel extends from October to April, with eggs laid in early November on Little Barrier Island and a month later on Codfish Island (8). They dig burrows in the soil in colonies, into which one egg is laid and incubated for 47 to 51 days. Adults forage at sea for periods of 2 to 13 days whilst feeding chicks (9), and chicks fledge after 88 days (2).

Migration to the east Pacific occurs over winter, when they will spend their nights feeding mainly on squid, crustaceans, and small fish. Cook’s petrels are most frequently seen feeding by surface-seizing; grabbing prey with their sharp bill from the ocean surface (2). Like all other petrels and closely related albatrosses, Cook’s petrel has a special digestive system consisting of an upper and lower stomach. Any oil from the petrel’s diet can be stored in the upper stomach, whilst the water, fat and proteins are digested as normal in the lower stomach. This oil acts as a constant source of energy as small amounts trickle into the lower stomach to be absorbed, but can also be regurgitated to feed their chicks. The oil is a sticky and foul-smelling liquid which also makes it an effective form of defence. If threatened, chicks will eject large quantities of the oil, which sticks onto the fur or feathers of a predator. Not only does this make the predator smell awful, the coated fur or feathers lose their insulating and waterproofing properties, which can be fatal (10).

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), and on Little Barrier Island the breeding success has dramatically risen from 5 to 70 percent (2). 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).

View information on this species at the UNEP World Conservation Monitoring Centre.

To learn more about conservation within the range of Cook’s petrel visit:

• Polar Conservation:
  www.polarconservation.org

For more information on this and other bird species please see:

• BirdLife International:
  http://www.birdlife.org