Data Zone
Justification of Red List category
This species qualifies as Vulnerable as it is only found on one small island. The accidental introduction of alien species could result in rapid population decline, or even extinction, as experienced by many other flightless island rails.
Population justification
A rat eradication attempt in 2011 reduced the population to probably <500 individuals, but because sufficient individuals were maintained in captivity during the eradication attempt, counts in 2013 and 2015 suggest that the population has largely recovered (S. Oppel and A. Bond in litt. 2016). In 2015, the total estimated abundance of Henderson Crakes (based on extrapolations from 25 point count stations and an assumed radius of origin of 100 m) was 8,513 birds (95% CI 5,755-12,749), equivalent to c.5,600 (3,800-8,400) mature individuals. These values are similar to estimations made (by different methods) of c.3,240 in 1987 and c.6,200 in 1992 (Graves 1992, Jones et al. 1995) indicating a fairly constant population over time.
Trend justification
Studies indicate that predation rates are low and reproduction rates are sufficient to replace birds lost. Estimated population sizes from 2015 (c.5,600 mature individuals) are similar to estimates made (by different methods) in 1987 (c.3240) and 1992 ([c.6,200] Graves 1992, Jones et al. 1995) indicating a fairly constant population over time.
Zapornia atra is endemic to Henderson in the Pitcairn Islands (to UK), a small uninhabited, raised-reef island in the south-central Pacific Ocean.
The species is found in dense to open forest throughout the island plateau, both in forest dominated by Pisonia and Pisonia/Xylosma and in Timonius thicket, also occurring in Pandanus-Thespesia-Argusia embayment forests and coconut groves on the beaches (Jones et al. 1995). It is omnivorous and appears to be an opportunistic feeder, taking advantage of seasonal increases in prey (Jones et al. 1995). It forages in the leaf-litter, gleaning items such as skink Emoia cyanura eggs from the undersides of fallen leaves, large nematodes, beetles, moths, spiders, dead caterpillars, land snails and small insects (Jones et al. 1995). The breeding season is long, extending from late July to mid February (double broods are not uncommon) and clutch-size is 2-3 (Jones et al. 1995). Helpers may provide extraparental care such as defending eggs and chicks from crabs and rats. Based on a small sample, adult annual survival is at least 43%, and reproductive success is a minimum of 0.95 chicks surviving to one month old per pair, per annum (Jones et al. 1995).
Although Polynesian Rat Rattus exulans takes 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). Henderson Crakes were affected by poison bait distributed on the island, and similar mortality needs to be anticipated in future eradication attempts (Oppel et al. 2016, Bond et al. 2019a,b). 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 Rallid populations. Diseases and exotic plant species are also potential future threats (Jones et al. 1995, Waldren et al. 1995).
Conservation Actions Underway
In 1988, Henderson was designated a World Heritage Site. Following a feasibility study (Brooke and Towns 2008) an attempt was made to eradicate rats from Henderson Island in 2011; this attempt was found to be unsuccessful, and rats returned to pre-eradication densities by 2013 (Bond et al. 2019b). A captive population of c.83 Henderson Crakes was established and maintained throughout the eradication operation to provide an insurance population. During this time the birds successfully bred in captivity and six chicks were released at the end of the operation along with the captive adults.
17 cm. Small, flightless rail. Glossy black with red eyes and legs. Voice Clattering clackety-clack call.
Text account compilers
Pilgrim, J., Berryman, A., Stattersfield, A.
Contributors
Bell, B., Bond, A., Brooke, M., Hall, J. & Oppel, S.
Recommended citation
BirdLife International (2024) Species factsheet: Henderson Island Crake Zapornia atra. Downloaded from
https://datazone.birdlife.org/species/factsheet/henderson-island-crake-zapornia-atra 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.