About Pterodroma cookii (G.R.Gray, 1843)
Cook's petrel, scientifically named Pterodroma cookii (G.R.Gray, 1843), is one of the smallest petrel species. Adults typically measure 25–30 cm (9.8–11.8 in) in length, have a 65–66 cm (26–26 in) wingspan, and weigh around 200 g (7.1 oz). Its plumage matches the typical pattern for gadfly petrels: it has pale grey upperparts with a dark grey "M" marking across the wings, and white underparts. It has a long, black bill with tubular nostrils positioned on both sides. Like all members of the order Procellariiformes, this nostril structure gives the species an exceptionally sharp sense of smell, which the birds use to find food and locate nest sites in the dark. Cook's petrel only breeds in New Zealand, on three small islands: Little Barrier Island, Great Barrier Island, and Codfish Island. Its breeding season falls during the southern hemisphere summer, running from October to May. It nests in burrows and rock crevices, and prefers nesting sites on thickly forested ridges. Its call is a three-part sequence of kek, kek, kek. The species was once more common than it is today; the current estimated total population is 1,258,000 individuals and the population is declining. It is classified as vulnerable because it breeds on only three small islands. While the population on Little Barrier Island remains stable, the populations on the other two islands are decreasing. On Great Barrier Island, introduced pigs, dogs, rats, and cats attack nests and burrows, as does the native flightless rail the weka; these predators prey on eggs and nestlings, reducing the island's population from an estimated 20,000 to just 100. Fossil evidence shows that before humans arrived in New Zealand, Cook's petrel bred on the mainland North and South Islands of New Zealand. When it is not breeding, Cook's petrel migrates from New Zealand to the Pacific Ocean. It has occasionally been sighted off the west coast of the United States and off the west coast of tropical South America.
