Justification of Red List Category
This species is listed as Critically Endangered owing to an ongoing range contraction caused by excessive predation by introduced mice. Mouse predation has forced this species out of coastal areas into sub-optimal upland habitat and is causing the population to decline. Urgent conservation intervention, which would also benefit the island's breeding seabirds, is needed to reverse this decline.
Modern population estimates have varied and may not accurately reflect population trends; there were thought to be c. 200 pairs in 1972-1974 (Richardson 1984) (substantially lower than previous estimates), 1,500 pairs in 1991 (P. G. Ryan in litt. 1999), 400-500 pairs in 2000-1 (Cuthbert and Sommer 2004) and 400-500 pairs in 2007 (Ryan and Cuthbert 2008).
Surveys of breeding territories indicate that density of territorial pairs roughly halved between 1990 and 2007, owing to predation by mice (Ryan and Cuthbert 2008).
Rowettia goughensis is endemic to Gough Island, Tristan da Cunha (Saint Helena, Ascension and Tristan da Cunha to UK) in the South Atlantic Ocean. Evidence suggests that it was much more common in the 1920s than at present (Ryan and Cuthbert 2008). The density of territorial pairs roughly halved between 1990 and 2007 (Ryan and Cuthbert 2008),
It is most common in tussock-grassland, wet heath and fjeldmark up to 800 m, and occurs at lower densities in fern-bush and peatbogs (Ryan and Cuthbert 2008). Breeding occurs from September to December, and chicks fledge in November and December. Clutch size is usually two eggs. The female constructs the nest, which is an open cup constructed on or close to the ground, sheltered by overhanging vegetation or a rock. Both sexes are involved in raising chicks (Ryan and Cuthbert 2008). It feeds primarily on invertebrates (80% of foraging time), but also eats fruit (Ryan and Cuthbert 2008), grass seeds, and scavenges broken eggs and birds (Richardson 1984). It nests on the ground amongst or under vegetation, but mostly on steep slopes or cliffs. Different plumage types suggest that it takes at least three years to acquire full adult plumage (Ryan and Cuthbert 2008).
The introduced House Mouse (Mus musculus) poses the greatest threat through competition (suspected) and predation (observed). Mice are known to have substantially altered invertebrate populations on other sub-Antarctic islands and R. goughensis is much less abundant on Gough than other bunting species on nearby mouse-free islands (Ryan and Cuthbert 2008). Recent research from Gough Island has shown that mice are a significant predator of breeding seabirds (Ryan and Cuthbert 2008), thus the probability is that bunting nests are depredated. Buntings are found at low density in the lowlands where mice are abundant on Gough Island, and predation rates of dummy eggs are up to thirty times higher in these areas (Cuthbert and Hilton 2004). The proportion of juveniles in the population has declined from 50% to 20% from 1991-2007, suggesting that recruitment is too low to sustain the population (Ryan and Cuthbert 2008). The accidental introduction of the Black Rat Rattus rattus from visiting ships is a potential threat as there have been occasional reports of rats on the supply ship and island, the last in 1983 (Wace 1986).
Conservation and Research Actions Underway
Gough is a nature reserve and World Heritage Site and is uninhabited apart from staff who run a meteorological station and a small research team (Cooper and Ryan 1994, A. Bond in litt. 2016). Territory mapping to investigate pair density in different habitats was conducted in 2000-2001, in addition to an assessment of the role of mice as nest predators (Cuthbert and Sommer 2004, Cuthbert and Hilton 2004). Further investigation of diet overlap with mice, and predation by mice was undertaken during 2003-2006. Following a 2006 review of the impacts of introduced rodents on Tristan da Cunha and Gough a feasibility study for mouse eradication was published in 2008. The study recommended what research still needed to be undertaken before an eradication effort should be attempted, and since 2008 researchers on the island have been conducting this work. A series of projects have investigated questions arising from the study (e.g. Cuthbert et al. 2011, Rexer-Huber and Parker 2011), and have shown an eradication operation is feasible. Operational planning and fundraising for the eradication of mice from Gough began in 2015 (J. Kelly, pers. comm. 2016)
Conservation and Research Actions Proposed
Carry out regular surveys to monitor the population. Eradicate mice from Gough Island (Ryan and Cuthbert 2008). Minimise the risk of other alien species becoming established on the island, particularly any rat Rattus species.
18 cm. Large, chunky, drab olive-coloured bunting. Male uniform dull olive-green overall with yellowish forehead and eyebrow. Underparts slightly paler dull olive with prominent black bib. Thick-based, pointed, black bill. Female and juvenile buffy-olive, heavily streaked above and below with dark brown. Apparently two streaky immature plumages occur, including transitional phase between juvenile streaky and adult olive plumage. Voice Contact call is keet keet and song is high, keening whistle.
Text account compilers
Benstead, P., Calvert, R., Ekstrom, J., Mahood, S., McClellan, R., Shutes, S., Stattersfield, A., Symes, A., Taylor, J., Wright, L & Stringer, C.
Cooper, J., Ryan, P.G. & Bond, A.
BirdLife International (2019) Species factsheet: Rowettia goughensis. Downloaded from http://www.birdlife.org on 12/12/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 12/12/2019.