| Nicobar pigeon | |
|---|---|
 | |
| An adult Nicobar pigeon on Ko Miang, off the southwest coast of Thailand | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Columbiformes |
| Family: | Columbidae |
| Genus: | Caloenas |
| Species: | C. nicobarica |
| Binomial name | |
| Caloenas nicobarica | |
| Synonyms | |
Columba nicobaricaLinnaeus, 1758 | |
TheNicobar pigeon orNicobar dove (Caloenas nicobarica,Car:ma-kūö-kö[3]) is abird found on small islands and in coastal regions from theAndaman and Nicobar Islands,India, east through theIndonesian Archipelago, to theSolomons andPalau. It is the only living member of the genusCaloenas alongside the extinctspotted green pigeon andKanaka pigeon, and is the closest living relative of the extinctdodo andRodrigues solitaire.
In 1738, the English naturalistEleazar Albin included a description and two illustrations of the Nicobar pigeon in hisA Natural History of Birds. When in 1758 the Swedish naturalistCarl Linnaeus updated hisSystema Naturae for thetenth edition, he placed the Nicobar pigeon with all the other pigeons in thegenusColumba. Linnaeus included a brief description, coined thebinomial nameColumba nicobarica and cited Albin's work.[4] The species is now placed in the genusCaloenas erected by English zoologistGeorge Robert Gray in 1840 with the Nicobar pigeon as thetype species.[5][6]
Twosubspecies are recognised:[6]
The two subspecies are very similar, withC. n. pelewensis being marginally smaller and with the elongated neck feathers being slightly shorter.[7]
Based oncladistic analysis ofmtDNAcytochromeb and 12SrRNAsequences, the Nicobar pigeon is sometimes called the closest living relative of theextinctdidines (Raphinae), which include the famousdodo (Raphus cucullatus).[8] However, the study's results showed this as one weak possibility from a limited sample oftaxa. In any case,nDNAβ-fibrinogenintron 7 sequence data agrees with the idea of the Raphinae as asubfamily of pigeons (and not an independent family, as was previously believed due to their bizarreapomorphies) that was part of a diverseIndopacificradiation, to which the Nicobar pigeon also belongs.[9]
The followingcladogram, from Shapiro and colleagues (2002), shows the Nicobar pigeon's closest relationships within Columbidae, aclade consisting of generally ground-dwelling island endemics.[8]
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A similar cladogram was published in 2007, differing only in the inverted placement ofGoura andDidunculus, as well as in the inclusion of thepheasant pigeon and thethick-billed ground pigeon at the base of the clade.[10]
C. nicobarica is a quite singularcolumbiform (though lessautapomorphic than theflightless Raphinae), as are for example thetooth-billed pigeon (Didunculus strigirostris) and thecrowned pigeons (Goura), which are typically considered distinct subfamilies. Hence, the Nicobar pigeon may well constitute another now-monotypic subfamily. And while any of the semi-terrestrial pigeons ofSoutheast Asia and theWallacea cannot be excluded as possible closest living relative of the Raphinae, the Nicobar pigeon makes a more plausible candidate than for example the group ofimperial-pigeons andfruit-doves, which seems to be part of the same radiation.[9]
Whether it is possible to clarify such deep-timephylogenies without a comprehensive study of all major lineages of livingColumbidae remains to be seen. The primitivemolecular clock used to infer the date the ancestors of the Nicobar pigeon and the didines diverged has since turned out to be both unreliable andmiscalibrated. But what little evidence is available still suggests that the Nicobar pigeon is distinct from all other living lifeforms since thePaleogene – most likely some time between 56-34million years ago during theEocene, which makes up the bulk of the Paleogeneperiod.[11]
Fromsubfossil bones found onNew Caledonia andTonga, anextinct species ofCaloenas, theKanaka pigeon (C. canacorum) was described. It was about one-quarter larger[12] than the Nicobar pigeon. Considering that it must have been a good source of food, it was most likely hunted to extinction by the first human settlers of its home islands. It probably was extinct by 500 BC. TheSpotted green pigeon (C. maculata) is a more recently extinct species from an unknownPacific locality; it probably disappeared in the 19th century and most likely succumbed to introducedEuropeanrats. It is placed inCaloenas as the least awkward possibility; its true affinities are presently indeterminate and it is perhaps more likely to represent a distinct genus of the Indopacific radiation of Columbidae.[13]
It is a large pigeon, measuring 32–35 cm (13–14 in) in length. The head is grey, like the upper neck plumage, which turns into green and copper hackles. The tail is short and pure white. The rest of its plumage is metallic green, appearing black in dull light. Thecere of the dark bill forms a small blackish knob; the strong legs and feet are dull red. Theirises are dark.[7][14]
Females, weighing 490–600 g, are on average slightly larger than the 460–525 g males, but with much overlap; they have a smaller bill knob, shorter hackles and browner underparts. Immature birds have a black tail and lack almost alliridescence. There is hardly any variation across the birds' wide range. Even the PalausubspeciesC. n. pelewensis merely has shorter neck hackles, but is otherwise almost identical.[7]
It is a very vocal species, giving a low-pitched repetitive call.[14]
On theNicobar Islands (which are referred to in itscommon andscientific names), the most significant colony of Nicobar pigeons in modern times was found onBatti Malv, a remotewildlife sanctuary betweenCar Nicobar andTeressa. The2004 Indian Ocean tsunami caused massive damage on the Nicobar Islands, and to what extent Batti Malv was affected is still not clear. But while everything on some islets in theGreat Nicobar Biosphere Reserve was destroyed, Batti Malvlighthouse – askeletal tower a dozen metres high, standing a few metresASL at the highest point of the low-lying island – was little-damaged and put back in operation by thesurvey shipINSSandhayak less than one month after the disaster. An April 2007 survey by theIndian Coast Guard vesselICGSVikram found the lighthouse tower "totally covered" invines, indicating rampant regeneration of vegetation – but perhaps also that damage to the island's forest was severe, as a cover of creeping plants is typical of earlysuccession stages, while a photo of the lighthouse taken before the tsunami shows rather mature forest.[15]
A Nicobar pigeon was found by theBardi JawiIndigenous rangers on theDampier Peninsula in the westernKimberley region ofAustralia in May 2017. As part ofbiosecurity measures, it was reported toquarantine services and was removed by Australian Department of Agriculture officials.[16][17][18] In 2023, another individual was found onGreen Island, off the coast ofCairns. Green Island Resort'senvironmental manager contacted authorities, but there are currently no plans to relocate the pigeon.[19]
The Nicobar pigeon's breeding range encompasses theAndaman and Nicobar Islands ofIndia, theMergui Archipelago ofMyanmar, offshore islands of south-westernThailand,Peninsular Malaysia, southernCambodia andVietnam, and many of the small islands betweenSumatra, thePhilippines and theSolomon Islands. OnPalau, the only distinctsubspeciesC. n. pelewensis is found.[14]
The Nicobar pigeon roams in flocks from island to island, usually sleeping on offshore islets where nopredators occur and spends the day in areas with better food availability, not shying away from areas inhabited by humans. Its diet consists ofseeds,fruit, and buds, and it is attracted to areas wheregrain is available. Agizzard stone helps to grind up hard food items. Its flight is quick, with regular beats and an occasional sharp flicks of the wings, as is characteristic of pigeons in general. Unlike other pigeons, groups tend to fly in columns or single file, not in a loose flock. The prominent white tail, visible in flight from behind, may serve as a sort of "taillight", helping keep flocks together when crossing the sea at dawn or dusk. The young birds' lack of a white tail is a signal of their immaturity clearly visible toconspecifics – to an adult Nicobar pigeon, it is obvious at a glance which flockmembers are neither potential mates, nor potential competitors for mates, nor old enough to safely guide a flock from one island to another.[14] When flying between islands, it typically flies high, at least 60 metres above the sea surface.[7]
This species nests in dense forest on offshore islets, often in large colonies. It builds a loose stick nest in a tree. It lays one elliptical faintly blue-tinged whiteegg.[14]
In 2017, several individualCaloenas nicobarica were sighted in theKimberley region ofWestern Australia with a juvenile captured atArdyaloon (One Arm Point), nearBroome - the first time the bird has been sighted on the Australian mainland.[20]
Nicobar pigeons are hunted in considerable numbers for food, and also for their gizzard stones which have sometimes been used injewellery.[21] The species is also trapped for the localpet market, but as it is onCITES Appendix I, commercial international trade is prohibited. Internationally,captive breeding is able to supply the birds demanded byzoos, where this attractive and unusual bird is often seen. Direct exploitation of the species, even including the illegal trade, might be sustainable on its own; however, its available nestinghabitat is decreasing. The offshore islets which it requires are oftenlogged forplantations, destroyed by construction activity, or polluted by nearbyindustry orharbours. 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. Though the bird is widely distributed and in some locations very common (even on small Palau it is still reasonably plentiful, with an estimated 1,000 adult birds remaining), its long-term future is increasingly in jeopardy. For these reasons, theIUCN considersC. nicobarica anear threatened species.[22]
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