The Nicobar pigeon is found on small islands and in coastal regions from the Andaman and Nicobar Islands, India, east through the Malay Archipelago, to the Solomons and Palau. It is the only living member of the genus Caloenas and may be the closest living relative of the extinct dodo, and the extinct Rodrigues solitaire.
In 1738, the English naturalist Eleazar Albin included a description and two illustrations of the Nicobar pigeon in his A Natural History of Birds. When in 1758 the Swedish naturalist Carl Linnaeus updated his Systema Naturae for the tenth edition, he placed the Nicobar pigeon with all the other pigeons in the genus Columba. Linnaeus included a brief description, coined the binomial name Columba nicobarica and cited Albin’s work. The species is now placed in the genus Caloenas that was introduced by the English zoologist George Robert Gray in 1840 with the Nicobar pigeon as the type species.
It is a large pigeon, measuring 40 cm (16 in) in length. The head is grey, like the upper neck plumage, which turns into green and copper hackles. The tail is very short and pure white. The rest of its plumage is metallic green. The cere of the dark bill forms a small blackish knob; the strong legs and feet are dull red. The irides are dark.
Females are slightly smaller than males; they have a smaller bill knob, shorter hackles and browner underparts. Immature birds have a black tail and lack almost all iridescence. There is hardly any variation across the birds’ wide range. Even the Palau subspecies C. n. pelewensis has merely shorter neck hackles, but is otherwise almost identical.