70Wildlife Conservation Plan for Seabirds

70 Wildlife Conservation Plan for Seabirds

Bulwer’s Petrel (Bulweria bulwerii)

TABLE Species information for the Bulwer's Petrel (Bulweria bulwerii)

Bulwer’s Petrel (Bulweria bulwerii) is a small all-dark petrel similar in size to small gadfly petrels (Pterodroma spp.) and prions (Pachyptila spp.) with strikingly long wings and long wedge-shaped tail. The species is pantropical, being found in all three oceans outside the breeding season. Breeding sites include the eastern Atlantic from the Azores, Portugal to Cape Verde, and the Pacific from eastern China and the Bonin Islands (Japan), east to the Hawaiian Islands (USA), and the Marquesas Islands (French Polynesia) (del Hoyo et al. 1992). The breeding season begins in April or May, with individuals forming colonies in a wide variety of habitats on offshore islands. Nests are usually in burrows, crevices, cracks or caves, under debris or vegetation cover (del Hoyo et al. 1992). After breeding, Bulwer’s Petrel migrate away from colonies but movements are not well understood. Birds are seen off north-west Australia between September and April and are thought to be on migration into the Indian Ocean. The diet comprises mainly of fish and squid, with minor proportions of crustaceans and sea-striders, feeding largely at night by surface-seizing.

Brooke (2004) estimated the global population to number between 500,000–1 million individuals. The Australian population is unknown but observations have increased off north-west Australia, Christmas Island and the islands of Ashmore Reef in recent decades. The population is suspected to be stable in the absence of evidence of any decreases or substantial threats.

Predation by cats (Felis catus) and Black Rats (Rattus rattus) occurs over portions of the breeding range (Cabral et al. 2005, Matias et al. 2009). Feral cats are considered a major driver of the present distribution of the species, on the Azores where breeding areas are restricted to steep cliffs. Black Rats are present on many of the islands on which the species breeds or would be likely to breed, and, along with cats, is thought to be one of the main determinants of the current breeding distribution. The species may be at risk of incidental capture in longline fisheries, but as yet, no significant effects of bycatch on adult mortality have been documented (Waugh et al. 2012). Due to the species foraging habit and wide range overlapping with commercial fishing areas, it is thought to suffer a heightened risk of mortality from oil spills and other marine pollution. Light pollution at night may be an important cause of mortality in some areas, and tourism and recreational developments may reduce available habitat in breeding colonies (del Hoyo et al. 2019).

Wildlife Conservation Plan for Seabirds 71

Wedge-tailed Shearwater (Ardenna pacifica)