Henderson Island Crake Zapornia atra Scientific name definitions

18 cm; male 69–87 (80)g, females 66–88 (74·5)g. Flightless; legs well developed for running. Entire plumage deep black with slight greyish gloss; iris, eyering , legs and feet red; bill blackish, yellowish green at base and along culmen. Sexes alike, but female has less yellowish green on bill (if present, this colour is confined to culmen ridge), and legs plain red to orange (red mottled with black in male); male's red eyering often blotched with black. Immature similar to adult but orbital ring dark, and legs and feet dusky. Juvenile greyer than adult on throat and underparts; iris brown; legs and feet black.

Henderson I, in C Pitcairn Group.

Thick Pisonia forest to open Pisonia/Xylosma forest, and Timonius thickets, of the island plateau, and Pandanus-Thespesia-Argusia embayment forest on some beaches; also in coconut groves. Absent only from low vegetation and pinnacled limestone at exposed S end of island.

Diet includes large nematodes, terrestrial molluscs, insects (Coleoptera, and adult and larval Lepidoptera), spiders, and eggs of the skink Emoia cyanura. Opportunistic feeder, taking advantage of seasonal increases in prey species. Forages by turning over leaf litter with bill , head-tossing litter aside, and scratching with feet; gleans prey items (including skink eggs) from undersides of leaves. Bold and curious. Active throughout the day .

Contact call a nasal “kak”, repeated in rapid series as an alarm call. Also has loud, continuous churring call uttered simultaneously as duet by pair members, sometimes joined by other family members. Most vocal at dawn and dusk.

Jul–Feb. Monogamous, with permanent pair-bond ; presumably permanently territorial. Possible polyandry once recorded, female making 4 nesting attempts with one male and 1 with a male from an adjacent territory. Some nests spherical, c. 20 cm in diameter with opening c. 10 cm wide, of shredded Pandanus palm leaves, placed up to 30 cm above ground in Pandanus leaf clump or at base of Pandanus trunk; others open-topped, built in low vegetation or up to 60 cm above ground in Asplenium nidus ferns. Male does most nest-building. Also builds roosting nests for use after hatching. Eggs 2–3; incubation 21 days, by both sexes; hatching synchronous; chicks have deep velvety black down, and black bill, legs and feet; leave nest soon after hatching; fed and cared for by both parents, helped by young of the previous brood and by other adults in family group; helpers also assist in protecting eggs and chicks from crabs and rats; young fully feathered and capable of independent foraging at c. 1 month, but remain associated with parents for much longer, sometimes being fed occasionally even when 15 weeks old. Many juveniles disperse from natal territories in Mar–Apr, but some remain with parents even when adult. Some pairs lay second clutch when young of first clutch are c. 1 month old; will also lay replacement clutches after loss of eggs or chicks. Annual adult survival at least 43%; reproductive success high, 2·45 chicks surviving for at least 6 months per pair per year. Recruitment rate not known, but probably compensates easily for annual losses, so that population is stable.

VULNERABLE. Restricted-range species: present in Henderson Island EBA. Endemic to Henderson I, a 37 km² uninhabited raised-reef island with no permanent fresh water. Last remaining flightless crake in the Pacific. Population estimated at c. 6200 mature birds in 1992, probably the carrying capacity of the island, as most territories (average size c. 1 ha) held more than 2 adults (1 Jones, P., Schubel, S., Jolly, J., Brooke, M. de L. and Vickery, J. (1995). Behaviour, natural history and annual cycle of the Henderson Island Rail Porzana atra (Aves: Rallidae). Biological Journal of the Linnean Society. Close ). No population change noted in 2003 BirdLife International (2016) Species factsheet: Zapornia atra. Downloaded from http://www.birdlife.org on 25/06/2016. . Main predator is Polynesian rat (Rattus exulans), introduced by man centuries ago; rats take eggs and chicks but apparently do not pose threat to survival of species, and the crakes are very aggressive towards them. An operation to eradicate R. exulans from the island was carried out in 2011, but was apparently not entirely successful, causing significant mortality and failing to eliminate rats (2 Howell, S.N.G. and van der Vliet, R.E. (2014). Endemic landbirds of Pitcairn and Henderson, South Pacific. Dutch Birding. 36(5): 332–339. Close , 3 Oppel, S., Lavers, J.L., Bond, A.L. and Harrison, G. (2016). Reducing the primary exposure risk of Henderson crakes (Zapornia atra) during aerial broadcast eradication by selecting appropriate bait colour. Wildlife Research. DOI: 10.1071/WR15198. Close ). Any inadvertent introduction of a more aggressive predator (e.g. another Rattus species) to the island could well result in the crake's rapid decline and extinction, as has happened with many other island rails. Species still vulnerable to possible human impacts: in 1982–83 a millionaire sought to make the island his home.