86Wildlife Conservation Plan for Seabirds

86 Wildlife Conservation Plan for Seabirds

Tahiti Petrel (Pseudobulweria rostrata)

TABLE Species information for the Tahiti Petrel (Pseudobulweria rostrata)

The Tahiti Petrel (Pseudobulweria rostrata) is a medium-sized dark-brown and white petrel with a sharply demarcated dark hood. The species is found over warm, tropical and subtropical water in the Pacific Ocean. The species breeds in the Marquesas, Society and Gambier Islands, French Polynesia, Fiji, American Samoa and New Caledonia (to France). It used to breed in Vanuatu (BirdLife International 2019) and may breed on Rarotonga, Cook Islands (Pratt et al. 1987), as well as on other islands. Two subspecies are distinguished: trouessarti in New Caledonia and rostrata in French Polynesia, the subspecific status of birds from other archipelagos remaining unclear, although Brooke (2004) assigned them to rostrata. This distinction is poorly supported by morphological (Villard et al. 2006) and genetic (Gangloff et al. 2012) data, and detailed analyses of vocalization differences between the two subspecies are missing. The Tahiti Petrel occurs predominantly off southeast Queensland and Northeast NSW in spring through to early autumn with numbers peaking with the arrival of juveniles in December. In some years, small numbers of these petrels remain off the eastern Australian coast. Of interest is the occurrence of this species off the northwest coast. It is not known where these petrels have originated from Pacific Island population; an unknown population breeding in Indonesia; or an unknown population breeding in the Indian Ocean. The species generally nests at high altitudes within forest or scrub on mountain steep slopes or rims and craters of volcanic islands, but also on low coralline or rocky hill islets and backshore. Eggs are laid in burrows or cavities located underneath large rocks, within cliffs or rocky boulders, or among large tree root systems. Birds generally nest in loose and small colonies. Breeding appears to occur throughout the year, although at least on Tahiti, there appears to be a peak between March and July (Villard et al. 2006). In the non-breeding season, the species disperses widely, and birds have been recorded as far east as the coast of Central America (Ballance et al. 2002), particularly Peru, Mexico (Onley and Scofield 2007) and Costa Rica (BirdLife International 2019).

The global population is estimated to be between 20,000–30,000 individuals. There are no recent data, however the species is thought to be decreasing, mainly due to nest predation by introduced predators and open cast mining activities. Marine surveys in the eastern tropical Pacific from 1988-2000 estimated a 35 per cent reduction between the periods 1988-1990 and 1998-2000 (Balance et al. 2002).

Predation and disturbance from non-native species represent the most serious threat to the species. Feral cats (Felis catus) have been identified as the greatest threat to the Tahiti Petrel, with predation impacting both chicks and adults. Petrel remains have been identified in 1-8 per cent of all cat scats (n=4,166) in large parts of the species range (Palmas et al. 2017). Rats (Rattus spp.), dogs (Canis familiaris) and pigs (Sus scrofa) are likely contributing to declines in reproductive success (BirdLife International 2019), with both dogs and pigs observed to dig out adults and chicks from their burrows (Villard et al. 2006). On Grand Terre (New Caledonia), the Marquesas and Society Islands, rat predation is an observed, but unquantified problem. In colonies where the soil is deep enough for Wedge-tailed Shearwaters (Ardenna pacifica) to nest, there can be intense competition for burrows (Villard et al. 2006).