Pterodroma incerta breeds only on Gough Island, Tristan da Cunha (St Helena to UK). It is absent from Nightingale Island where there is no suitable habitat, and probably also from Inaccessible Island, although it is possible that a small number of birds could breed there (P. G. Ryan in litt. 1999). The species's occurrence on Tristan da Cunha is unclear; in 1972-1974 the population there was estimated to be 100-200 pairs, and there may only be a few scattered pairs remaining. On Gough Island, the first quantitative population estimate indicates a total of around 1.8 million pairs (Cuthbert 2004), which is considerably larger than the earlier estimate of at least 20,000 pairs (P. G. Ryan in litt. 1999). However, a recent estimate taking into account the occupancy rates of burrows which are suitable for the species halves this number and suggests a population size of 860,000 pairs, varying between 630,000 and 1,100,000 pairs (Rexer-Huber et al. 2014), and several studies revealed very low breeding success of less than 20% (Cuthbert and Hilton 2004, Wanless et al. 2007, Dilley et al. 2015). At sea, it is practically restricted to the South Atlantic, occurring off the east coast of South America to the west coast of Africa (Enticott 1991, P. G. Ryan in litt. 1999), occasionally rounding the Cape of Good Hope into the Indian Ocean (Hobbs in litt. 2009).

Conservation Actions Underway

On Tristan da Cunha, a programme to eradicate cats was successful in the 1970s. However, searches on Tristan da Cunha have failed to locate any birds (Wanless et al. 2007). Gough Island is a nature reserve and World Heritage Site (Cooper and Ryan 1994). The first ever quantitative population survey was undertaken on Gough Island in 2000/2001, together with research into the species's breeding ecology and reproductive output (Cuthbert 2004, Cuthbert and Hilton 2004). Between 2003 and 2007, and again between 2010 and 2014, further research on reproductive output and mouse predation was conducted (Wanless et al. 2007, Cuthbert et al. 2013, Rexer-Huber et al. 2014, Dilley et al. 2015). Burrow density and occupancy as well as breeding success are monitored annually on Gough Island (A. Bond in litt.)

Conservation Actions Proposed

Eradicate mice from Gough Island. Minimise the risk of further introduced species establishing on Gough Island, particularly any rat Rattus species (P. G. Ryan in litt. 1999). Confirm the status of the population on Tristan da Cunha and assess whether birds breed on Inaccessible Island. Measure demographic rates on Gough Island to better understand population trends.