VU
Henderson Crake Zapornia atra



Justification

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
Numbers were estimated at c.3,240 in 1987 (Graves 1992) and, using a different technique, c.6,200 birds in 1992; no major change in population size was evident in 2003 (Jones et al. 1995, M. Brooke pers. comm. 2007). 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 estimated abundance of Henderson Crakes at 25 point count stations was 213 (95% CI 144-319) individuals, which would result in an overall population estimate of 8512 (95% CI 5755 -  12749) individuals assuming a survey radius of 100 m around each point (S. Oppel and A. Bond in litt. 2016). Although recruitment to the breeding population is not known, numbers of surviving chicks probably compensate for annual losses such that the population can be considered stable despite the continued presence of rats (Jones et al. 1995).

Trend justification
Studies indicate that predation rates are low and reproduction rates are sufficient to replace birds lost, thus the population is suspected to be stable.

Distribution and population

Zapornia atra is endemic to Henderson in the Pitcairn Islands (to UK), a small uninhabited, raised-reef island in the south-central Pacific Ocean. 

Ecology

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).

Threats

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). Other possible introductions, such as other Rattus species, diseases and exotic plant species, are potential future threats (Jones et al. 1995, Waldren et al. 1995).

Conservation actions

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 (Churchyard et al. 2013). 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. 

Conservation Actions Proposed
Periodically resurvey to monitor numbers and trends. Ensure that further alien species are not accidentally introduced to Henderson. Re-attempt the eradication of Pacific rats from Henderson Island.

Identification

17 cm. Small, flightless rail. Glossy black with red eyes and legs. Voice Clattering clackety-clack call.

Acknowledgements

Text account compilers
Benstead, P., Derhé, M., Mahood, S., O'Brien, A., Pilgrim, J., Stattersfield, A., Stringer, C.

Contributors
Bell, B., Hall, J., Bond, A., Oppel, S., Brooke, M.


Recommended citation
BirdLife International (2021) Species factsheet: Zapornia atra. Downloaded from http://www.birdlife.org on 06/12/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 06/12/2021.