Location and General Description
The Nicobar Islands consist of twenty-two islands of varying size and are located in the eastern Indian Ocean as part of the Bay of Bengal. The Nicobars are separated from the Andamans in the north by a 150-km-wide channel and are 189 km from Sumatra to the southeast. The climate of the Nicobar Islands is warm tropical, with temperatures ranging from 22 to 30°C and 3,000-3,800 mm annual average rainfall. Rainfall is heavily influenced by monsoons, which come from the southwest (May to September) and the northeast (October to December). The only perennial rivers are found on Great Nicobar.
The islands are geologically part of long island arch that runs from Arakan Yoma in Myanmar to the Mentawai Islands off Sumatra and include the Andamans and many underwater sea mounts. The arch was formed as the uplift along the subduction of the Indian-Australian plate in the late Eocene or early Oligocene. Isolation of the Nicobars from the mainland resulted from the opening of the Andaman Sea in the middle Miocene about 10.8 m.y. ago. Unlike the Andamans, which are thought to have been connected to mainland Myanmar during periods of falling sea levels of the Pleistocene, the Nicobars remained as islands. Falling sea levels during this time joined many of the islands into three distinct groups, each of which has its own biological character today: Great Nicobar in the south (including Great Nicobar, Little Nicobar, Meroe, and satellites), Nancowry and the middle Nicobars (Nancowry, Katchall, Camorta, Teressa Chaura, and Tillanchong), and Car Nicobar to the north (including Car Nicobar and Batti Malv). The highest point in the Nicobars is Mt. Thullier, at 670 m. The higher elevations of the Nicobars often contain serpentine and gabbro formations, whereas at lower elevations Eocene sediments (sandstones, shales, and siltstones) with ultrabasic igneous intrusions predominate (Rao 1996). Great Nicobar contains younger substrates from the Tertiary that are more like the soils of parts of Sumatra than the other islands.
The vegetation of the Nicobars typically is divided into the coastal and mangrove forests and the interior evergreen and deciduous forests. Additionally, Kamorta, Katchall, Nancowry, and Car Nicobar all contain extensive interior grasslands, but these are thought to be anthropogenic in origin (Rao 1996; Daniels 1996). The grasslands are composed mainly of Imperata cylindrica, Saccharum spontaneum, Heteropogon contortus, Chloris barbata, Chrysopogon aciculatus, and Scleria cochinchinensis, along with many herbs and shrubs. Evergreen forests of Great Nicobar, Kamorta, and Katchall are dominated by Calophyllum soulattri, Sideroxylon longipetiolatum, Garcinia xanthochymus, Pisonia excelsa, and Mangifera sylvatica. Other important species of Kamorta and Katchall are Artocarpus peduncularis, Radermachera lobbi, Symplocos leiostachya, and Bentinckia nicobarica. Deciduous forests occur at lower elevations on Great Nicobar and include Terminalia procera and T. bialata.
The isolation of the Nicobars has given rise to a number of endemic plant and animal species. The Nicobar Islands Rain Forests [IM0133] contain twenty-five native mammal species, four of which are strict endemics (table 1). The majority of species are bats, and rodents (all rats) are the second most numerous order. Several larger species exist, however, including wild pig (Sus scrofa) and Nicobar macaque (Macaca fascicularis umbra). There is also a unique tree-shrew (Tupaia nicobarica), which is the most arboreal member of its genus. All four endemics in table 1 are considered threatened by IUCN (categories VU and above) (IUCN 2000).
Table 1. Endemic and Near-Endemic Mammal Species.
Sorcidae Crocidura nicobarica*
Tupaiidae Tupaia nicobarica*
Pteropodidae Pteropus faunulus*
Muridae Rattus palmarum*
An asterisk signifies that the species' range is limited to this ecoregion.
There are eighty-two native, nonpelagic bird species in the Nicobars, and nine of them are endemic (table 2). The list of endemics matches the list of nine restricted-range species from BirdLife International's Nicobar Islands EBA (Stattersfield et al. 1998). There are also many species and subspecies shared only with the Andamans (Sankaran 1997, 1998). Two of the endemics are threatened (VU or above) (Megapodius nicobariensis, Hypsipetes nicobariensis) (IUCN 2000).
Table 2. Endemic and Near-Endemic Bird Species.
Family Common Name Species
Accipitridae Nicobar serpent-eagle Spilornis minimus*
Accipitridae Nicobar sparrowhawk Accipiter butleri*
Megapodiidae Nicobar scrubfowl Megapodius nicobariensis**
Columbidae Andaman wood-pigeon Columba palumboides
Columbidae Andaman cuckoo-dove Macropygia rufipennis
Psittacidae Nicobar parakeet Psittacula caniceps*
Strigidae Andaman hawk-owl Ninox affinis
Sturnidae White-headed starling Sturnus erythropygius
Pycnonotidae Nicobar bulbul Hypsipetes nicobariensis*
An asterisk signifies that the species' range is limited to this ecoregion.
**Megapodius nicobariensis is currently limited to the ecoregion but was formerly found in the Andamans as well.
The types of birds present in the Nicobars are particularly interesting. There are very high numbers of some groups, including eight heron species, seven hawk species, six kingfisher species, and six pigeon species. However, there are no babblers, only two sylvine warblers, and just one bulbul species.
The Nicobar Islands have forty-three reptile species, of which eleven are endemic. Eleven amphibian species (all frogs and toads) are in the Nicobars; two are endemic.
The Nicobars are more similar to Sumatra and Malaysia botanically than to Burma, Thailand, or even the Andamans. In fact, the Nicobars and Andamans share only 28 percent of angiosperm species. The Nicobars contain more than 580 flowering plant species. A rate of endemism for the angiosperms is available only for the Nicobars and Andamans jointly and is about 14 percent of all species.
Protected areas cover about 30 percent of the Nicobar islands, and only 14 percent of the ecoregion's native forest has been lost (table 3). Unfortunately, the protected areas, as they currently stand, are not situated with regard to the distribution of endemic species (Das 1999; Sankaran 1997). Sankaran (1997) describes several key unprotected sites for endemic birds that are important for all taxa. This includes the southern tip of Great Nicobar, which not only contains the greatest number of endemic birds in all the Nicobars but also is the largest uninhabited lowland forest in the ecoregion. The southern tip is also one of the most susceptible to future development. A large portion of Great Nicobar is dominated by the Great Nicobar Biosphere Reserve, which consists of two national parks: Campbell Bay National Park and Galathea National Park. The two parks are separated by a 12-km buffer zone that is uninhabited primary forest. Sankaran (1997) argues that the buffer zone should be designated as national park to preserve what is currently a large contiguous forest, thus preventing roads or other disturbance from bisecting the biosphere. The Nancowry group of islands is also in need of expanded protected areas. It has levels of bird endemism matching the other two island groups but a much higher percentage of threatened species (Sankaran 1997).
Table 3. Protected Areas That Overlap with the Ecoregion, Derived from Sankaram (1997).
Protected Area Area (km2) IUCN Category
Batti Malv Wildlife Sanctuary 2 ?
Tillanchong Wildlife Sanctuary 17 ?
Megapod Island Wildlife Sanctuary 0.13 ?
Galathea National Park 110 ?
Campbell Bay National Park 426 ?
Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.
Types and Severity of Threats
Habitat conversion poses the greatest threat to the ecoregion. Aboriginal peoples have inhabited the Nicobars for at least 2,000 years and are estimated to have converted about 10 percent of the forest cover in that time. Settlement programs brought mainlanders to the Nicobars starting in the late 1960s; they now make up 36 percent of the population. Just in the past twenty-five years, 4 percent of the Nicobars' original forest cover has been lost to mainlanders. The settlement program no longer exists, but the Nicobars are still at a critical juncture where decisions about how to control development and conserve its resources must be made. There are proposals to make the Nicobars a major tourist destination, make Great Nicobar a free trade port, and increase the military presence on the islands. Road development and cash crop promotion (particularly rubber and cashews) are also future threats. Wildlife exploitation threatens the edible-nest swiftlet in the Nicobars, the Nicobar megapode, crocodiles, and sea turtles (Das 1999; Sankaran 1997).
Justification of Ecoregion Delineation
Following MacKinnon (1997), we placed the Andaman Islands in a distinct ecoregion, the Andaman Islands Rain Forests [IM0101]. However, we included the Nicobar Islands Rain Forests [IM0133] in this bioregion based on recommendations by Tim Whitmore (pers. comm., 1999). Udvardy (1975) placed both island chains into the Andaman and Nicobar Islands biogeographic province.
References for this ecoregion are currently consolidated in one document for the entire Indo-Pacific realm.
Indo-Pacific Reference List
Prepared by: John Lamoreux