Justification of Red List Category
This species, the smallest flightless bird in the world, qualifies as Vulnerable because, although abundant, it is restricted to one tiny island and is at permanent risk from chance events such as the accidental introduction of alien predators.
The population has been variously estimated as 1,200 birds in 1938 (Hagen 1952), 5,000-10,000 birds in 1952 (Elliott 1957) and 1,000-2,000 breeding pairs in 1974 (Richardson 1984). The most accurate survey to date gave an estimate of 8,400 birds (Fraser et al. 1992), roughly equivalent to 5,600 mature individuals.
The population is suspected to be stable in the absence of any immediate and serious threats.
Atlantisia rogersi is confined to the South Atlantic island of Inaccessible, Tristan da Cunha (St Helena to UK). It is abundant on the island and may be at carrying capacity given its high population density, delayed maturity, small clutch-size, and lack of major predators or competitors (Fraser et al. 1992, Taylor 1998).
Behaviour This species is sedentary and flightless (Taylor and van Perlo 1998, del Hoyo et al. 1996). It is monogamous, and lives in family groups (Collar and Stuart 1985), holding small territories at a density of up to 10-15 birds per hectare in good quality habitat (Taylor and van Perlo 1998, P. G. Ryan in litt. 2000). Breeding occurs from October to January (P. G. Ryan in litt. 2000). Habitat It occurs virtually throughout the island, on most vegetation types, at all altitudes, and even on the steepest slopes (Taylor and van Perlo 1998). Breeding Breeding has been recorded in coastal tussock-grass Spartina arundinacea, especially where this is mixed with the fern Blechnum penna-marina to form luxurian undergrowth and mats of vegetation (Collar and Stuart 1985, Taylor and van Perlo 1998). Nests have also been found in beds of sedge on the plateau (Collar and Stuart 1985), where the species often occurs in open fern-bush habitats and island-tree thickets, generally away from the cliffs (P. G. Ryan in litt. 2000). It inhabits heathland at the island's highest altitudes (Taylor and van Perlo 1998). In general it prefers areas where vegetation, boulders or other landscape features at ground level provide tunnels in which to shelter and to breed (Collar and Stuart 1985). Non-breeding It forages in every available habitat including very short vegetation, boulder beaches and marshy areas (Fraser et al. 1992). It is absent from one site of short dry tussocks on cinder cones (Collar and Stuart 1985, Taylor and van Perlo 1998). Diet The diet comprises a wide range of invertebrates including earthworms and moths, centipedes, and a wide variety of insects and insect larvae, as well as berries and seeds (Collar and Stuart 1985, Taylor and van Perlo 1998). Breeding site Nests are built on the ground beneath a dense cover of vegetation (Taylor and van Perlo 1998). They are carefully woven from the vegetation in which they are sited, usually oval or pear-shaped, and accessed via a track or tunnel extending for up to 50cm through the vegetation (Taylor and van Perlo 1998). A clutch consists of two eggs (P. G. Ryan in litt. 2000).
Predation by Tristan Thrush Nesocichla eremita and wet weather are believed to be the main causes of chick mortality, but pose no real threat. However, there is a permanent risk that the island will be colonised by mammalian predators, particularly the black rat Rattus rattus from Tristan. The colonisation of potential competitors would also be a threat, as well as alien invertebrates which could negatively modify the prey base (P. G. Ryan in litt. 1999). Despite its name, the island is now more accessible to islanders via small boats based at Tristan (P. G. Ryan in litt. 1999).
Conservation Actions Underway
Inaccessible is a nature reserve and, although Tristan Islanders retain the right to collect driftwood and guano, other access is restricted (Cooper et al. 1995). A management plan for the island was published in 2001, and updated in 2010 (Ryan and Glass 2001, RSPB and TCD 2010); this is being updated again in 2016. Inaccessible was added to the Gough Island World Heritage Site in 2004 (RSPB and TCD 2010). New Zealand flax has been removed from coastal and plateau areas and is now confined to c.300 m of cliffs around the Waterfall (P. G. Ryan in litt. 2012).
17 cm. Small, very dark rail. Dark grey on underparts and dark rusty-brown on upperparts. Short black bill, greyish legs and red eye. Immature is overall brownish in colour with dark eye. Adults show various degrees of white barring on flanks and belly. Voice Loud, trilling call, various soft contact tchik calls, and harsh, loud chip alarm call.
Text account compilers
Ekblom, R., McClellan, R., Shutes, S., Stattersfield, A., Symes, A. & Taylor, J.
Cooper, J. & Ryan, P.G.
BirdLife International (2020) Species factsheet: Atlantisia rogersi. Downloaded from http://www.birdlife.org on 29/10/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 29/10/2020.