Medium-sized flightless rail, related to banded rail (Gallirallus phillipensis) of mainland New Zealand. Differs from banded rail with its shorter wings, longer tail and legs and a strongly down-curved bill (Tennyson & Martinson 2006).
Crown and nape dark rusty brown. Grey line from bill over eye to nape; broad chestnut brown band from bill through eye meeting on back of neck.
Upper back and wing coverts yellowish brown with black and rufous brown barring and spotting. Primaries chestnut with broad bars of brownish black. Secondaries brown with chestnut notches.
Throat pale grey with a band of white-barred black at base of neck. Breast rufous brown barred with black; belly black barred with white. Undertail coverts black barred with rufous brown. Bill brown with darker tip. Iris reddish brown. Feet brown. (Oliver 1955).
Derived from a flighted ancestor in the banded rail group. DNA evidence suggests Dieffenbach’s rail and the much smaller flightless extinct endemic Hutton’s rail (Cabalus modestus) may have derived from the same ancestral species (Worthy & Holdaway 2002).