Gough moorhen  (Gallinula comeri)

The Gough moorhen is a medium-sized, thickset, almost flightless bird that resembles the common moorhen (Gallinula chloropus) (2) but is smaller, stockier and with shorter wings (3). The head, neck and underparts are a sooty-black, while the mantle is brown and the tail is tipped in white (2). Unlike the common moorhen, the white plumage on the flanks is either missing or reduced (3). The beak is yellow at the tip, changing to red at the base of the bill, which continues up between the eyes to the forehead (2) (3). The legs are red to orange in colour with greenish-yellow blotches (3).

Originally endemic to Gough Island in the Tristan da Cunha group in the South Atlantic Ocean. However, seven birds were also introduced to neighbouring Tristan Island in 1956, where this species' close relative, the Tristan moorhen (G. nesiotis), had become extinct at the end of the 19th century. In 1983, the Gough population was estimated at 2,000-3,000 pairs and, in 1984, the Tristan population was estimated at around 250 pairs and increasing (2). It has been disputed whether the birds living at present on Tristan are descendants of introduced Gough moorhens (G. comeri) or in fact part of a recovering remnant population of the original Tristan moorhen (G. nesiotis), classified as extinct (4). Current opinion is generally that the former is the case (5).

On Gough, the moorhen is found near the coast in boggy areas and close to streams, commonly in fern-bush but sometimes in tussock grass. On Tristan, where no tussock remains, the bird is found in fern-bush (2).

The Gough moorhen is a monogamous species, forming breeding pairs that defend a territory together. Breeding occurs from September to March, peaking between October and December on Gough (2). Both sexes construct a cup-shaped nest in the grass, made from sticks, into which two to five eggs are laid. The eggs are incubated for approximately 21 days, also by both sexes. Two broods are possible in a year and, if managed, the first brood will help with the rearing of the second (3).

This species feeds on vegetable matter, seeds, invertebrates and carrion, and scavenges petrel carcasses and garbage. Invertebrates are often foraged for in abandoned and active albatross nests, as well as petrel burrows (2). Interestingly, it actively hunts mice and preys on unattended eggs of burrowing petrels (6).

Although stable or even increasing in numbers, its occurrence in a restricted habitat on only two islands makes this species extremely vulnerable to chance events such as fires, hurricanes and disease epidemics (4). Additionally, despite surviving with introduced rats on Tristan, the accidental introduction of predators to Gough remains a risk. Indeed, it is likely that the Gough moorhen's close relative, the extinct Tristan moorhen (G. nesiotis), disappeared from Tristan as a result of predation by the black rat (Rattus rattus), though this may have been in combination with feral cat predation, habitat destruction and hunting by islanders. The Gough moorhen appears able to cope with current levels of rat predation on Tristan, but the accidental introduction of this, or any other, predator to its stronghold on Gough still remains the greatest risk facing this species (2).

A cat eradication programme on Tristan in the 1970s was highly successful, helping to protect the Gough moorhen and other endangered native birds (2). Unfortunately, as an introduced species to Tristan, the Gough moorhen is considered alien, and therefore not protected there under the Tristan da Cunha Conservation Ordinance (5). The bird's stronghold on Gough, however, is well protected, with the island being a nature reserve and World Heritage Site, and uninhabited apart from the staff that run a meteorological station (2). Gough Island is the least disturbed major cool-temperate island ecosystem in the South Atlantic Ocean, and hosts one of the most important sea-bird colonies in the world. Indeed, with 54 bird species, 22 breeding species and four threatened species, the island will probably continue to be well protected indefinitely, preserving this rich biodiversity and protecting the Gough moorhen for many years to come (7).

For further information on the Gough moorhen see:

BirdLife International:
http://www.birdlife.org/datazone/species

Twycross Zoo Animal Information Sheet:
http://www.twycrosszoo.com/PDF/gough%20moorhen.pdf

Authenticated (15/12/08) by Ross Wanless and Andrea Angel, Percy Fitzpatrick Institute of African Ornithology. 
http://www.fitzpatrick.uct.ac.za