Data Zone
Justification of Red List category
This species qualifies as Vulnerable as it is only found on one small island, where it remains at risk from the accidental introduction of alien species, especially mammalian predators.
Population justification
Estimates over the past three decades have been broadly congruent. In 1987, the population was estimated to number c.13,000 individuals (value adjusted to correct island area) and available habitat was apparently saturated (Graves 1992). In 1991-1992 surveys, using a different technique, 11,000 individuals were estimated, a number also thought true in 2003 and 2011 (M. Brooke in litt. 2007-2012). In 2015, the population at 25 point count locations was extrapolated to the area of suitable habitat, equal to 7,194 (5,875-8,593) individuals (Bond et al. 2019a). Because the latter estimate was based on detectability distances that were not empirically determined, these results are treated with some caution, although their proximity to earlier data suggest that the population size of this species is between 6,000 and 13,000 individuals, thought equivalent to c.4,000-8,600 mature individuals.
Trend justification
Although direct comparison is hampered by methodological differences, count data between 1987 and 2015 are comparable (Graves 1992, Brooke and Jones 1995, Bond et al. 2019a) and do not indicate any decline. Since 2015, there is no identified threat that may have caused a reduction.
Acrocephalus taiti is endemic to Henderson, an uninhabited island in the Pitcairn Islands (to UK).
This is a forest species, typically found in family groups, and foraging at all levels. It has a varied diet, which is known to include several species of land snails, ants, flies, beetles, cockroaches, large wasps, seeds and fruit pulp (Graves 1992). It has a well-defined breeding period from late August to early January, nesting in a wide variety of tree species in the lower canopy of forest. The species breeds either in pairs or trios, commonly of unrelated birds, probably a consequence of the island's stable habitat and climax forest, where young birds may be more able to secure a nesting territory when belonging to a trio than a pair (Brooke and Hartley 1995). Clutch-size is two to three and, once hatched, most chicks fledge. Predation by introduced Polynesian Rats (Rattus exulans) is the main cause of nest failure (Brooke and Hartley 1995).
Although Polynesian Rat Rattus exulans may take eggs and chicks, there is no indication that the species is unduly threatened by this predation as the two have co-existed on Henderson possibly since the 8th century (Jones et al. 1995). In August 2011, an attempt was made to eradicate R. exulans from Henderson island, but this failed and rat populations recovered by 2013 (Churchyard et al. 2013). Other possible introductions, such as other Rattus species (e.g. R. rattus or R. novergicus) could cause rapid future declines and extinction, as they have other insular Acrocephalus populations. Diseases and exotic plant species are also potential future threats (Waldren et al. 1995).
Conservation Actions Underway
In 1988, Henderson was designated a World Heritage Site. Following a feasibility study (Brooke and Towns 2008) a rat eradication operation was attempted on Henderson Island in August 2011, but this failed and rat density returned to pre-eradication levels by 2013 (Churchyard et al. 2013, Bond et al. 2019b).
17 cm. Large warbler with relatively short bill. Adult olive-brown above, white below with slight yellowish tinge. Mottled olive-brown and white crown, rest of head white with dark streak through eye. White feathers variably and often asymmetrically scattered among darker feathers. Some individuals are nearly all white. Voice No song. Call a harsh, short note.
Text account compilers
Berryman, A.
Contributors
Bell, B., Bond, A., Brooke, M., Hall, J., Mahood, S., O'Brien, A. & Oppel, S.
Recommended citation
BirdLife International (2024) Species factsheet: Henderson Island Reed-warbler Acrocephalus taiti. Downloaded from
https://datazone.birdlife.org/species/factsheet/henderson-island-reed-warbler-acrocephalus-taiti on 23/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 23/12/2024.