Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
Brooke (2004) estimated the global population to number c.500,000-1,000,000 individuals, while national population estimates include: c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in China; < c.100 breeding pairs and c.1,000-10,000 individuals on migration in Taiwan and c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in Japan (Brazil 2009). The European population is estimated at 6,100 pairs, which equates to 12,100 mature individuals (BirdLife International 2015).
The population is suspected to be stable in the absence of evidence for any declines or substantial threats. The European population trend is unknown (BirdLife International 2015).
This 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).
This species is marine and higly pelagic, usually being found far from land except during the breeding season. Its diet comprises mainly of fish and squid, with minor proportions of crustaceans and sea-striders, feeding largely at night by surface-seizing. The breeding season begins in April or May, with individuals forming colonies in a wide variety of habitats on offshore islands. Nests can be burrows, crevices, cracks or caves, under debris or vegetation cover (del Hoyo et al. 1992).
The following information refers to the species' European range only: Predation by cats Felis catus, House Rats Rattus rattus and endemic invertebrates occurs in large portions of the breeding range in the North East Atlantic (Cabral et al. 2005, Matias et al. 2009). Feral cats are considered a major driver of the present distribution of the species, for example on the Azores where breeding areas are restricted to steep cliffs wherever cats are present and local extinctions may have been caused by cat predation in the past. House 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. In one colony on Madeira predation of Shearwater chicks by Madeiran Wall Lizards Teira dugessii has been recorded in up to 10% of nests, however no overall impact on colony breeding success has been found and lizard predation is highly unlikely to have an impact on the species on a population level (Matias et al. 2009).
The large colony in Desertas Island, Madeira suffers intense human exploitation for food or fish bait, which also occurs at a lower level in other North East Atlantic sites, although not in the Salvage Islands, Madeira following the declaration of the islands as a national park (Carboneras et al. 2014). 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 many commercial fishing lanes, it is thought to suffer a heightened risk of mortality from oil spills and other marine pollution. Light pollution at night might be an important cause of mortality in some areas, and tourism and recreational developments may reduce available habitat in breeding colonies on the Canary Islands, Madeira and Azores (Carboneras et al. 2014).
Conservation Actions Underway
The species is listed under Appendix II of the Bern Convention, and under Annex I of the EU Birds Directive. In Europe it is currently listed as occurring in 26 marine Important Bird Areas. In the EU it is listed within 23 Special Protection Areas.
Conservation Actions Proposed
The following information refers to the species's European range only: Ongoing management and eradication of invasive predators at breeding colonies; enforcement and regulation of human exploitation; mitigation and reduction of light pollution from shipping and human settlements; bycatch monitoring on board vessels and reduction and mitigation on fishing vessels where appropriate.
Text account compilers
Ashpole, J, Butchart, S., Calvert, R., Bennett, S., Ekstrom, J., Fjagesund, T., Martin, R., Newton, P.
BirdLife International (2021) Species factsheet: Bulweria bulwerii. Downloaded from http://www.birdlife.org on 16/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 16/10/2021.