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 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). The population trend is not known, but the population is not believed to be decreasing sufficiently rapidly to approach the thresholds under the population trend criterion (>30% decline over ten years or three generations). For these reasons the species is evaluated as Least Concern.
Brooke (2004) claimed a population size of 800,000-1,000,000 individuals.
Population trends are unknown for this species. Rats predate on eggs and chicks at peripheral populations, but this may not impact the global population size (S. Oppel in litt. 2019). For example, nesting success is poor (17%) on Henderson Island, where rat eradication attempts have not been successful (Churchyard et al. 2013, Brooke 2019). However, the two largest colonies, on Ducie and Oeno, have been rat-free since 1997, with the latter now increasing in size (Brooke et al. 2018).
Pterodroma ultima breeds in the Pitcairn Islands (to UK), the Tuamotu Archipelago, the Austral Islands (Garnett 1984) and the Gambier Islands (French Polynesia) (Thibault and Bretagnolle 1999), Easter Island and Salas y Gomez, Chile (Flores et al. 2014) and perhaps in the Cook Islands and the Juan Fernandez Islands (Flood et al. 2016). In the Pitcairns, an estimated 2,500 (± 500) bred on Henderson, 12,500 (± 2,500) on Oeno, and 250,000 (± 29,000) on Ducie (Brooke 1995). Following rat eradication on Oeno in 1997, the population there had grown to at least 25,000 pairs in 2013 (M. Brooke in litt.). In the Tuamotus, colonies occur on Mururoa and Fangataufa (Holyoak and Thibault 1984), although these may have disappeared owing to nuclear tests and the recent construction of an airstrip (V. Bretagnolle in litt. 1999, J.-C. Thibault in litt. 2000). In the Australs, it breeds only on a limited number of islets off Rapa, where the population was estimated at 10-100 pairs in 1990 (Thibault and Varney 1991). In the Gambiers, proof of breeding was found for the first time on Manui and numbers were estimated at 5-10 pairs (Thibault and Bretagnolle 1999). In the Cook Islands, a specimen was collected probably from Rarotonga or perhaps one of the other southern Cook Islands, between c.1899 and 1904 (Gill 1996). In 2009, 2 pairs were reported nesting on Easter Island (M. Martin in litt. 2011). Non-breeding dispersal has been investigated via geolocators; it takes the birds to the central North Pacific at approx 40-45oN (M. Brooke, in litt). Bailey et al. (1989) and Kenyon et al. (2009) reported that the species had been also observed in the Gulf of Alaska.
The species has been recorded nesting in rocky cliffs during March. On Henderson Island, has been recorded nesting in woodland behind beaches or in low fern scrub close to the island’s cliffs. Nesting is seasonal, with egg-laying between late May and early July. 50-day incubation period is completed in three stints. The male takes the first stint, averaging 19.3 days, following a similar stint by the female, and then the male for the second time. Egg-hatching normally occurs towards the end of the male’s second stint (Brooke 2010). Off-duty incubating birds can travel over 4,800 km from Henderson towards the coast of Peru (Clay et al. 2017). Breeding sites are completely abandoned during the non-breeding period, after November. They feed mainly at sea on cephalopods, fish and small crustaceans (Imber et al. 1995).
Pacific rats (Rattus exulans) depredate eggs and chicks at peripheral populations, but this may not impact the global population size (S. Oppel in litt. 2019). For example, nesting success is poor (17%) on Henderson Island, where rat eradication attempts have not been successful (Churchyard et al. 2013, Brooke 2019). However, the two largest colonies, on Ducie and Oeno, have been rat-free since 1997, with the latter now increasing in size (Brooke et al. 2018).
This species breeds on islands with a maximum elevation of 33 m and, as such, may be vulnerable to sea-level rise.
Conservation Actions Underway
Although the species breeds at a small number of locations and may be declining at some of these, the eradication of rats on Oeno and Ducie in 1997 (Bell and Bell 1998) secures the largest populations. Following a feasibility study (Brooke and Towns 2008) a rat eradication operation was carried out on Henderson Island in August 2011 but the continuing presence of rats was confirmed in 2012.
Conservation Actions Proposed
Monitor the Ducie population. Continue searches for the species in the Tuamotus (V. Bretagnolle in litt. 1999). Continue the programme of Pacific rat eradication on Henderson.
Text account compilers
Mahood, S., Martin, R., Moreno, R., Fjagesund, T., Anderson, O., Stuart, A., Smith, D., Calvert, R., Hermes, C., O'Brien, A.
Bretagnolle, V., Brooke, M., Clay, T., Morgan, K., Thibault, J.-C., Taylor, G.A. & Oppel, S.
BirdLife International (2022) Species factsheet: Pterodroma ultima. Downloaded from http://www.birdlife.org on 04/12/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 04/12/2022.