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Henderson Crake Zapornia atra

Justification
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.

Taxonomic source(s)
del Hoyo, J.; Collar, N. J.; Christie, D. A.; Elliott, A.; Fishpool, L. D. C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.

Taxonomic note
Zapornia atra (del Hoyo and Collar 2014) was previously placed in the genus Porzana.

Synonym(s)
Nesophylax ater Collar and Andrew (1988), Porzana atra North, 1908

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

Distribution and population
Porzana atra is endemic to Henderson in the Pitcairn Islands (to UK), a small uninhabited, raised-reef island in the south-central Pacific Ocean. 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). 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 (Jones et al. 1995).

Population justification
Jones et al. (1995) estimated the population to number 6,200 mature individuals, roughly equivalent to 9,300 individuals in total.


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.

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, a rat eradication operation was carried out on Henderson Island to eradicate R. exulans from the island and a follow-up monitoring expedition is planned for 2013 to assess the success of the project (J. Hall in litt. 2012). However, other possible introductions, such as Black Rat R. rattus (a more aggressive predator than R. exulans), diseases and exotic plant species, are a potential threat (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) a rat eradication operation was carried out on Henderson island in August 2011 (J. Hall in litt. 2012). A captive population of c.80 Henderson Crakes was established and maintained throughout the eradication operation to minimise risk from non-target poisoning. During this time the birds successfully bred in captivity and six chicks were released at the end of the operation. A follow-up monitoring expedition is planned for 2013 to assess the success of the rat eradication.
Conservation Actions Proposed
Periodically resurvey to monitor numbers and trends. Ensure that further alien species are not accidentally introduced to Henderson.


Related state of the world's birds case studies

References
Graves, G. R. 1992. The endemic land birds of Henderson Island, southeastern Polynesia: notes on natural history and conservation. Wilson Bulletin 104: 32-43.

Jones, P.; Schubel, S.; Jolly, J.; Brooke, M. De L.; Vickery, J. 1995. Behaviour, natural history, and annual cycle of the Henderson Island Rail Porzana atra (Aves: Rallidae). Biological Journal of the Linnean Society 56: 167-183.

Waldren, S.; Florence, J.; Chepstow-Lusty, A. J. 1995. Rare and endemic vascular plants of the Pitcairn Islands, south-central Pacific Ocean: a conservation appraisal. Biological Conservation 74: 83-98.

Further web sources of information
Explore HBW Alive for further information on this species

Search for photos and videos, and hear sounds of this species from the Internet Bird Collection

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

Contributors
Bell, B., Brooke, M., Hall, J.

IUCN Red List evaluators
Butchart, S., Symes, A.

Recommended citation
BirdLife International (2014) Species factsheet: Zapornia atra. Downloaded from http://www.birdlife.org on 24/11/2014. Recommended citation for factsheets for more than one species: BirdLife International (2014) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 24/11/2014.

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

To provide new information to update this factsheet or to correct any errors, please email BirdLife

To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.

Key facts
Current IUCN Red List category Vulnerable
Family Rallidae (Rails, Gallinules, Coots)
Species name author North, 1908
Population size 9300 mature individuals
Population trend Stable
Distribution size (breeding/resident) 41 km2
Country endemic? Yes
Links to further information
- Additional Information on this species