The generic distinction of the Gough Island flightless Gallinule

The presence of five specimens of Gough Island Gallinules, Porphyriornis nesiotis comeri ALLEN, in the Zoological Gardens of Amsterdam originating from the remote Gough Island situated within the subantarctic confines of the South Atlantic Ocean, offered a favourable occasion for a study of these peculiar and rare birds. The Gough Island Gallinule is presently the only surviving representative of its species; the Tristan da Cunha form, P. nesiotis nesiotis (P. L. SCLATER), having been exterminated by man probably nearly a century ago. It belongs to a group of rails of which also the Moorhen or Common Gallinule, Gallinula chloropus, is a representative. From the latter species it differs among others by having greatly reduced powers of flight. One can wonder, however, about the degree of relationship between members of the genus Gallinula on the one hand and the Gough Island Gallinule on the other hand. In fact, the general appearance of the Gough Island Gallinule is that of a very stout, strongly legged Common Gallinule with a more skulking, less graceful gait. The birds in captivity in the Amsterdam Zoo were very pugnacious, a habit which has also been recorded by previous authors. When in pursuit of each other the birds frequently uttered a sharp, rattling call, which was also described by HOLDGATE (1958) from birds observed in Gough Island and transliterated as a rapid “chack-chack”. It seems that this call has not been recorded from any member of Gallinula chloropus. In spite of these differences RIPLEY (1954), in reviewing the “genera” Gallinula, Porphyriornis and Ionornis, has doubted the justification of the use of a separate genus name for the Flightless Gallinules from Tristan and Gough Island, which he would prefer to treat as members of the genus Gallinula. This question will again be considered here.