James Bulwer, a Scottish clergyman and amateur naturalist, is credited with collecting the type specimen of Bulwer's Petrel on islands off Portugal (the Desertas) for Sir William Jardine in 1828. More interested in conchology and archaeology, Bulwer contributed little else to ornithology and lived out the remainder of his life quietly in Norfolk, Scotland.
As obscure in the world of ornithology as Reverend Bulwer was himself, the Bulwer's Petrel-small, sooty brown and nocturnal-is one of the least well known of the Procellariiformes. It is one of two species in the genus. The other is Jouanin's Petrel (Bulweria fallax), which is restricted to the northwest Indian Ocean.
Bulwer's Petrel nests on small islands off the main Hawaiian Islands, the northwestern Hawaiian Islands, and on a few other islands in the North and South Pacific, eastern North Atlantic, and Indian oceans. The largest breeding colony-an estimated 75,000-100,000 pairs-is on the small volcanic island of Nihoa, approximately 600 km northwest of the main Hawaiian island of Kauai.
Few aspects of the breeding biology of this petrel have been studied comprehensively, especially at colonies in the Pacific and Indian Oceans. Principal studies of breeding biology have been made by Jouanin et al. (Jouanin et al. 1979), Mougin (Mougin 1989, Mougin 1990, Mougin 1991a, Mougin 1991b), and Mougin et al. (Mougin et al. 1992). Still, little is known of this species' courtship and mating behavior, and incubation periods and patterns of nestling growth have just recently been reported (see Breeding: incubation, below; Amerson and Shelton 1976, Whittow 1994). No subspecies have been described, but breeding phenology differs considerably for colonies on the Cape Verde, Phoenix, and Marquesas Islands, compared to other colonies in the Pacific and Atlantic Oceans.
Bulwer's Petrel spends less than six months each year at breeding colonies; the remainder of its time is spent at sea. Colonial and nocturnal, it does not excavate its own burrow like many others in the family Procellariidae; rather it lays a single, white egg in rock ledges or crevices, in human-made or natural cavities, or in the burrows of other species. Pairs remain faithful to both nest site and mate for several years, announcing their return to the breeding colony with sharp, barking calls from the ground near the burrow entrance. Both sexes incubate and feed the young, which reach one and a half times the average mass of the adult by 50 days of age. The young leave the nest at night when their flight feathers still are not fully developed, and immature birds are not observed on land again for at least two years.
In the nonbreeding season, this species migrates to areas of rich nutrient upwellings. Little is known of its feeding during this season, but the most important prey species collected from birds near the breeding grounds are hatchetfishes (Sternoptychidae) and lanternfishes (Myctophidae). Bulwer's Petrel is not known to follow ships. It feeds solitarily or in pairs, sitting on the surface, spreading its wings and dipping its head beneath the surface.
Although this species is not threatened or endangered, intense human exploitation and predation by cats (Felis domesticus) and rats (Rattus sp.) in much of its range pose conservation concerns. Extirpation of the Bulwer's Petrel from individual colonies may be a threat, since it is not known whether young birds return only to their natal colonies, or are part of a larger population.