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Bermuda Petrel | Pterodroma cahow
Bermudastormvogel | Petrel de las Bermudas
The Bermuda Petrel, known locally as the cahow, breeds only on a few small rocky islets of Bermuda, outside the Caribbean. It was considered extinct for almost three centuries until 18 breeding pairs were rediscovered in 1951. Outside the breeding season it feeds in the north-western Atlantic and around the Azores. It is included in this guide because it occurs north of the region and closely resembles Black-capped Petrel.
Voice
Almost silent at sea. At the breeding islets, high, scratchy calls at night; in display the male gives a long, high call ending in a sharp eek, the female a lower, growling or moaning reply.
Recording: Robert L. Flood — CC BY-NC-SA 4.0 · converted to mono · xeno-canto
Identification
35–38 cm. A medium-sized, slender gadfly petrel with long wings angled at the wrist and a short, thick, black hooked bill. Upperparts dark grey-brown, wings and tail almost black. The dark cap continues over the hindneck and sides of the neck onto the sides of the breast, giving a hooded look; forehead and throat are white. A narrow, variably distinct pale band across the uppertail coverts. Underparts white, with long white undertail coverts. Underwing white with a broad dark leading edge and a narrower dark trailing edge. It flies in high, swinging arcs.
Confusion species
Black-capped Petrel Pterodroma hasitata is very similar but slightly larger and usually has a white hindneck and a broad white rump; its dark form shows less white and so comes close to Bermuda Petrel. A certain identification requires sharp photographs of the head, rump and underwing. Pale Trindade Petrels Pterodroma arminjoniana have a dark breast band and a dark rump. Great Shearwater Ardenna gravis is larger, with a slender bill, a dark belly patch and a flatter flight.
Habitat
Open ocean over deep water, mainly over the continental slope and along the edges of the Gulf Stream; there are no records from inshore waters. It breeds in burrows on small rocky islets; most pairs use artificial nest burrows.
Where the bird is most at home, classified by the vegetation types of the Caribbean.
Range and movements
No documented records from the Caribbean were found in the sources consulted; any reports from in or near the region are unconfirmed. There is no range map, as there is too little material from the region. The nearest regular records come from the Gulf Stream off North Carolina, where it has been seen a few dozen times since 1983. Birds tracked with loggers fed as far as Nova Scotia, the Gulf of St Lawrence and the Grand Banks; outside the breeding season many stay around the Azores. In May 2014 a bird was photographed off western Ireland.
How and when to look
A record in the region is highly unlikely. Any Black-capped Petrel with little white on the hindneck and rump needs sharp photographs of the upperside and underside; without documentation a report will not be accepted.
Conservation status
Endangered. In 2019, 132 pairs bred, and around 2015 the world population was about 300 birds. Hurricanes and rising sea level erode the low breeding islets. Competition for burrows with White-tailed Tropicbirds, rats and artificial light also play a part. Artificial nest burrows have allowed numbers to grow slowly. No regular presence in the Caribbean.
Scientific name
Pterodroma cahow | (Nichols & Mowbray, 1916)
Nichols & Mowbray described the species in 1916 as Aestrelata cahow; 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. cahow is the old Bermudian vernacular name of the bird, imitating its eerie nocturnal call. The specimen the first description was based on came from Castle Island, Bermuda.