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). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely 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 exceed 15,000,000 individuals.
The population is suspected to be declining owing to predation from invasive species.
This species breeds on Gough Island and Tristan da Cunha (St Helena to UK) in the south Atlantic, and on the Chatham Islands, New Zealand and south of New Zealand's south island. Adults are thought to remain in waters adjacent to colonies; however young birds occur north of the colonies to Australia and South Africa.
The diet of this species is comprised mostly of cruaceans (especially copepods), squid and some fish. It apparently takes more crustaceans in summer and small squid in winter. Prey is obtained usually by hydroplaning and by filtering or surface-seizing. Breeding starts in July or August and individuals are strongly colonial, nesting in burrows which are sometimes occupied by more than one pair. It breeds on a large variety of substrates and areas; coastal slopes, flat lava fields, offshore islets and cliffs, dry rocky soil, caves and scree (del Hoyo et al. 1992).
The main threats faced by the Broad-billed Prion come from introduced predators. House Mice on Gough are dramatically impacting reproductive success and causing very rapid population declines (Cuthbert et al. 2013, Dilley et al. 2015). Estimates of breeding success were only 6% across the 2009/10 and 2010/11 breeding seasons (Cuthbert et al. 2013), and chick mortality in 2014 was complete (Dilley et al. 2015). The population by 2000/01 had already been estimated to have reduced by more than 80% since the 1960s (Carboneras et al. 2018). Rapid declines and local extinctions have occurred following the introduction of other invasive predators to breeding islands, including rats and stoats in Dusky Sound, Fiordland, cats on Herekopare Island and Weka on Jacky Lee Island (Miskelly 2013).Severe weather events also pose a threat. A severe storm in 2010 caused considerable mortality on breeding islands around Stewart Island (Miskelly 2013), and predicted increases in the frequency and ferocity of such storms may impact part of the population sufficiently to impact the global abundance of the species.
Text account compilers
Fjagesund, T., Butchart, S., Hermes, C., Ekstrom, J., Martin, R., Newton, P., Stuart, A., Calvert, R.
BirdLife International (2022) Species factsheet: Pachyptila vittata. Downloaded from http://www.birdlife.org on 24/09/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 24/09/2022.