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Cook's Petrel | Pterodroma cookii
Cooks stormvogel | Petrel de Cook
Cook's Petrel is a small petrel of the genus Pterodroma that breeds only on a few islands of New Zealand. After the breeding season it crosses the Pacific to the east, and in the northern summer large numbers stay far off the coasts of Baja California and California. In the guide area it is a summer visitor of the open ocean, almost never seen from land.
Voice
Silent at sea. In the colonies at night high, rapidly repeated calls in flight over the forest.
Recording: Nathan El — CC BY-NC-SA 4.0 · converted to mono · xeno-canto
Identification
25–30 cm. A small, slender petrel with long, pointed wings, often held crooked, and a short black bill. Upperparts pale grey, with a dark M-shaped band across the wings and back; the tail is grey with a dark terminal band. Forehead and underparts white, with a dark patch through and below the eye. The underwing is almost entirely white, with only a narrow dark margin and a short dark bar at the carpal. Flies fast and agile in high, swinging arcs over the waves, with short series of wingbeats. Sexes alike.
Confusion species
Shearwaters such as Townsend's Shearwater Puffinus auricularis and Black-vented Shearwater Puffinus opisthomelas are dark above, without an M pattern, have a longer, thin bill and fly low with quick, stiff beats. Tahiti Petrel Pseudobulweria rostrata is larger, with a dark head, breast and underwing. Other small Pterodroma species, which may turn up far offshore off the west coast as rare visitors, differ in the pattern of head, tail and underwing and can be identified with certainty only from good photographs.
Habitat
Open ocean, usually well beyond the edge of the continental shelf and often hundreds of kilometres offshore; rarely comes close inshore. Takes small squid, fish and crustaceans from the surface, partly at night. Breeds in burrows in montane forest on islands of New Zealand.
Where the bird is most at home, classified by the vegetation units of Mexico and Central America.
Range and movements
In the guide area mainly far off the west coast of Baja California, on passage in April and May and as a summer visitor from June to September; in the Gulf of California and further south far off Mexico only scattered records. How far the species occurs along the Pacific coast of Central America is unclear because of the small number of observations far out at sea. Outside the guide area it breeds on Hauturu (Little Barrier Island) and Whenua Hou (Codfish Island) in New Zealand; outside the breeding season many birds stay in the eastern Pacific, from Peru and Chile north to off California.
- Summer visitor (c. Apr–Sep)
- Winter visitor (c. Oct–Mar)
- Passage (Mar–Apr, Oct–Nov)
- dark = core range, pale = thinly spread
How and when to look
Only long pelagic trips far off the coast of Baja California, mainly from May to September, offer a chance of an encounter. The pale grey upperparts with a dark M, the almost entirely white underwing and the fast, high-arcing flight are the best features.
Conservation status
Vulnerable. The species breeds on only two islands. Introduced cats and rats once greatly reduced the population; since these predators were eradicated from the breeding islands it has increased again. Artificial light, which disorients young birds, and changes in food supply at sea remain risks.
Scientific name
Pterodroma cookii | (Gray, 1843)
Gray described the species in 1843 as Procellaria Cookii; because it was later moved to another genus, the author and year stand in brackets. The genus Pterodroma was introduced in 1856 by Bonaparte. Pterodroma is Greek, from pteron 'wing' and dromos 'runner', after the fast, sweeping flight. cookii honours the British explorer Captain James Cook (1728–1779). The specimen the first description was based on came from New Zealand.