Zapornia atra 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Aves Gruiformes Rallidae

Scientific Name: Zapornia atra (North, 1908)
Common Name(s):
English Henderson Crake, Henderson Island Crake, Henderson Island Rail, Red-eyed Crake
Nesophylax ater (North, 1908) — Collar and Andrew (1988)
Porzana atra North, 1908
Taxonomic Source(s): del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A. and Fishpool, L.D.C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Volume 1: Non-passerines. Lynx Edicions BirdLife International, Barcelona, Spain and Cambridge, UK.
Taxonomic Notes: Zapornia atra (del Hoyo and Collar 2014) was previously placed in the genus Porzana.
Identification information: 17 cm. Small, flightless rail. Glossy black with red eyes and legs. Voice Clattering clackety-clack call.

Assessment Information [top]

Red List Category & Criteria: Vulnerable D2 ver 3.1
Year Published: 2016
Date Assessed: 2016-10-01
Assessor(s): BirdLife International
Reviewer(s): Butchart, S. & Symes, A.
Contributor(s): Brooke, M., Hall, J., Bell, B., Oppel, S. & Bond, A.
Facilitator/Compiler(s): Benstead, P., Derhé, M., Mahood, S., O'Brien, A., Pilgrim, J., Stattersfield, A., Stringer, C.
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.

Previously published Red List assessments:

Geographic Range [top]

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

Countries occurrence:
Additional data:
Estimated area of occupancy (AOO) - km2:43Continuing decline in area of occupancy (AOO):No
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:46
Continuing decline in extent of occurrence (EOO):NoExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:1Continuing decline in number of locations:No
Extreme fluctuations in the number of locations:No
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population: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.
Current Population Trend:Stable
Additional data:
Number of mature individuals:8200Continuing decline of mature individuals:No
Extreme fluctuations:NoPopulation severely fragmented:No
No. of subpopulations:1Continuing decline in subpopulations:Unknown
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:Yes
No. of individuals in largest subpopulation:100

Habitat and Ecology [top]

Habitat and 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).

Continuing decline in area, extent and/or quality of habitat:Unknown
Generation Length (years):2.7
Movement patterns:Not a Migrant

Threats [top]

Major Threat(s): 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 [top]

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.

Citation: BirdLife International. 2016. Zapornia atra. The IUCN Red List of Threatened Species 2016: e.T22692711A93366374. . Downloaded on 26 September 2018.
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