Justification of Red List Category
This species qualifies as Near Threatened because although rats have been eradicated at the largest breeding population, the population continues to slowly decline within its moderately small range.
There are no data, however the species is presumably declining slowly due to predation of eggs and young by rats.
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 in2013 (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.
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 range up to 4500 km from Henderson towards the coasts of Peru (T. Clay et al., in prep.). Breeding sites are completed abandoned during the non-breeding period, after November. They feed mainly at sea on cephalopods, fish and small crustaceans (Imber et al. 1995).
Pacific rat Rattus exulans is present on some islands, and causes low breeding success ( less than 5%; Brooke 1995, 2010) on Henderson in particular. The Henderson population could be sustained through immigration from other colonies but there is no evidence that this occurs (Brooke 2010). The species is potentially threatened by climate change because it has a geographically bounded distribution: it is restricted to an island or islands with a maximum altitude of 33 m (BirdLife International unpublished data). There is no information on trends.
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
Anderson, O., Calvert, R., Mahood, S., Moreno, R., O'Brien, A.
Thibault, J., Morgan, K., Brooke, M., Bretagnolle, V., Clay, T.
BirdLife International (2018) Species factsheet: Pterodroma ultima. Downloaded from http://www.birdlife.org on 25/06/2018. Recommended citation for factsheets for more than one species: BirdLife International (2018) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 25/06/2018.