Justification of Red List Category
This species is listed as Endangered because it has a very small population which may be continuing to decline on the one tiny island where it occurs, as a result of habitat degradation and predation by introduced mammals. In the absence of robust evidence on population trend or size, it is suggested that a precautionary approach should be taken and it should be assumed that this species is at risk due to the tiny area it occupies, and the likely impact of introduced and invasive species.
In 1998-1999, its population was estimated at c.2,000-3,000 individuals and increasing dramatically following the partial, but temporary control of feral cats Felis catus and Pacific rats Rattus exulans (B. and D. Bell verbally 1999, M. Brooke in litt. 2005). However, by 2005 numbers of Pacific rats and feral cats had recovered (M. Brooke in litt. 2005), which may have been accompanied by a reduction in numbers of the species. Efforts are now being made to obtain a more definite population estimate (A. Schofield, pers. comm. 2016).
There are no new quantitative data on population size and trends; however, since the unsuccessful eradication of feral cats and Pacific rats, the species is suspected to be declining at a slow rate as the populations of these pests recover.
Acrocephalus vaughani is endemic to the tiny volcanic island of Pitcairn in the Pitcairn Islands (to UK).
It is most common in patches of tall forest, and present in low numbers around dwellings and in scrubland, but absent from cliffs and patches of open ground (Pratt et al. 1987). It is insectivorous, rarely foraging at ground-level perhaps because of the presence of cats and humans. It appears to breed only in pairs, unlike Henderson Reed-warbler A. taiti, which forms breeding groups, possibly related to the greater disturbance and consequent year-to-year instability of the habitat on Pitcairn (Brooke and Hartley 1995). However, more recently, breeding in groups has been noted (E. and D. Bell verbally 1999).
Vegetation on the island has been greatly modified and today only remnants of forest remain with scrub and grassland elsewhere. In recent years there has been an increase in the spread and range of Rose Apple (Syzigium jambos) which is encouraged for honey production but threatens the native Pitcairn vegetation (E. and D. Bell in litt. 2007). Clearance of native vegetation for gardening and browsing by goats also decreases the range of available habitat for the bird as does the subsequent spread of other introduced plant species (E. and D. Bell in litt. 2007). It is likely to be predated by Pacific rats and feral cats; however, after two unsuccessful eradication attempts there is scepticism about the chances of a third attempt succeeding. Pitcairn is currently subject to several development proposals, and a new harbour has just been constructed, reducing the habitat available for this species (C. Stringer in litt. 2016). Feral goats were subject to an eradication attempt, but it unclear whether the island remains free of feral goats in 2016.
Conservation Actions Underway
The feral cat eradication was successful in 1997 (M. Brooke in litt. 2005). Domestic cats were reintroduced to the wild by the island residents in 1999 - stating it was to control the rats after the failure of efforts to eradicate Pacific rats (E. and D. Bell in litt. 2007). A programme to eradicate rats in 1997-1998 (Bell and Bell 1998) was unsuccessful. The increases in numbers of A. vaughani in 1998-1999 were probably the result of temporarily reduced predation pressure, as has been seen with A. taiti on Henderson Island (A Bond, S. Oppel in litt. 2016). Numbers of feral cats have since increased (M. Brooke in litt. 2005).
17 cm. Large warbler with relatively short bill. Adult olive-brown above, yellowish-white below, with dark streak through eye and pale superciliary. White feathers variably and often asymmetrically scattered among darker feathers. Immatures brown above, rich tawny below without white feathers.
Text account compilers
Derhé, M., Mahood, S., O'Brien, A., Stattersfield, A., Symes, A., Taylor, J., Stringer, C.
Oppel, S., Hall, J., Brooke, M., Bell, E., Bond, A., Bell, D., Bell, B., Stringer, C.
BirdLife International (2020) Species factsheet: Acrocephalus vaughani. Downloaded from http://www.birdlife.org on 12/07/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 12/07/2020.