The Nicobar pigeon is a large beautiful bird found mainly in South East Asia and Oceania. It is the only living member of the genus Caloenas and may be the closest living relative of the extinct flightless birds dodo and Rodrigues solitaire. Nicobar pigeons have developed a bright plumage; their 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 their plumage is metallic green. The cere of the dark bill forms a small blackish knob; the strong legs and feet are dull red. 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.
Nicobar pigeons are 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. They inhabit rainforests, dry forests, mangroves, and shrubland.
Nicobar pigeons are highly nomadic and roam in flocks from island to island, usually sleeping on offshore islets where no predators occur; they spend the day in areas with better food availability, not shying away from areas inhabited by humans. Nicobar pigeons are most active at dawn and dusk and prefer to feed singly or in pairs. Although these birds spend most of their time on the forest floor, they are powerful flyers; their flight is quick, with regular beats and an occasional sharp flick of the wings, as is characteristic of pigeons in general. Unlike other pigeons, groups of Nicobar pigeons tend to fly in columns or single file, not in a loose flock. The white tail is prominent in flight when seen from behind and may serve as a sort of "taillight", keeping flocks together when crossing the sea at dawn or dusk. Nicobar pigeons are very vocal birds and in order to communicate with each other, they give a low-pitched repetitive call.
Nicobar pigeons are monogamous and it is believed that pairs mate for life. Their breeding season varies with locations but usually occurs from January to March. Nicobar pigeons nest in dense forest on offshore islets, often in large colonies. They build a loose stick nest in a tree usually in undisturbed sites or just below the canopy. The female lays one elliptical faintly blue-tinged white egg and both parents incubate it around 2.5 weeks. The chick is altricial; it hatches helpless and is fed by the adults with a rich crop milk fluid until it becomes independent at about three months of age.
Nicobar pigeons are hunted in considerable numbers for food, and also for their gizzard stone (a rock held inside a bird's stomach) which is used in jewelry. The species is also trapped for the local pet market, although such trade is generally illegal. Nicobar pigeons are also threatened by the decrease of the available nesting habitat. The offshore islets which they require are often logged for plantations, destroyed by construction activity, or polluted by nearby industry or harbors. Also, increased travel introduces predators to more and more of the breeding sites, and colonies of the Nicobar pigeon may be driven to desert such locations or be destroyed outright.
The IUCN Red List and other sources don’t provide the total population size of the Nicobar pigeon. According to the Wikipedia resource, there are only 1,000 adult birds occur on Palau (island country). Currently, Nicobar pigeons are classified as Near Threatened (NT) on the IUCN Red List and their numbers today are decreasing.