The Sunda rhinoceros (Rhinoceros sondaicus) or lesser one-horned rhinoceros, or more popular as Javan rhinoceros, is a very rare member of the family Rhinocerotidae and one of five extant rhinoceroses. It belongs to the same genus as the Indian rhinoceros, and has similar mosaicked skin, which resembles armour, but at 3.1–3.2 m (10–10.5 feet) in length and 1.4–1.7 m (4.6–5.8 ft) in height, it is smaller (in fact, it is closer in size to the black rhinoceros of the genus Diceros). Its horn is usually less than 25 cm (10 inches), smaller than those of the other rhino species. Only adult males have horns; females lack them altogether. Once the most widespread of Asian rhinoceroses, the Sunda rhinoceros ranged from the islands of Java and Sumatra, throughout Southeast Asia, and into India and China. The species is critically endangered, with only one known population in the wild, and no individuals in captivity. It is possibly the rarest large mammal on earth,:21 with a population of as few as 40 in Ujung Kulon National Park at the western tip of Java in Indonesia. A second population in Cat Tien National Park in Vietnam was confirmed as extinct in 2011. The decline of the Sunda rhinoceros is attributed to poaching, primarily for their horns, which are highly valued in traditional Chinese medicine, fetching as much as US$30,000 per kilogramme on the black market.:31 As European presence in their range increased, trophy hunting also became a serious threat. Loss of habitat, especially as the result of wars, such as the Vietnam War, in Southeast Asia, has also contributed to the species' decline and hindered recovery. The remaining range is within one nationally protected area, but the rhinos are still at risk from poachers, disease and loss of genetic diversity leading to inbreeding depression. The Sunda rhino can live approximately 30–45 years in the wild. It historically inhabited lowland rain forest, wet grasslands and large floodplains. The Sunda rhino is mostly solitary, except for courtship and offspring-rearing, though groups may occasionally congregate near wallows and salt licks. Aside from humans, adults have no predators in their range. The Sunda rhino usually avoids humans, but will attack when it feels threatened. Scientists and conservationists rarely study the animals directly due to their extreme rarity and the danger of interfering with such an endangered species. Researchers rely on camera traps and fecal samples to gauge health and behavior. Consequently, the Sunda rhino is the least studied of all rhino species. Two adult rhinos with their calves were filmed in a motion-triggered video released on February 28, 2011 by WWF and Indonesia's National Park Authority, which proved it is still breeding in the wild. In April 2012, the National Parks Authority released video showing 35 individual Sunda rhinos, including mother/offspring pairs and courting adults. The Sunda rhinoceros is a solitary animal with the exception of breeding pairs and mothers with calves. They will sometimes congregate in small groups at salt licks and mud wallows. Wallowing in mud is a common behavior for all rhinos; the activity allows them to maintain cool body temperatures and helps prevent disease and parasite infestation. The Sunda rhinoceros does not generally dig its own mud wallows, preferring to use other animals' wallows or naturally occurring pits, which it will use its horn to enlarge. Salt licks are also very important because of the essential nutrients the rhino receives from the salt. Male home ranges are larger at 12–20 km² (5–8 miles²) compared to the female, which are around 3–14 km² (1–5 mi²). Male territories overlap each other less than those of the female. It is not known if there are territorial fights. Males mark their territories with dung piles and by urine spraying. Scrapes made by the feet in the ground and twisted saplings also seem to be used for communication. The Sunda rhinoceros is herbivorous, eating diverse plant species, especially their shoots, twigs, young foliage and fallen fruit. Most of the plants favored by the species grow in sunny areas in forest clearings, shrubland and other vegetation types with no large trees. The rhino knocks down saplings to reach its food and grabs it with its prehensile upper lip. It is the most adaptable feeder of all the rhino species. Currently, it is a pure browser, but probably once both browsed and grazed in its historical range. The rhino eats an estimated 50 kg (110 lb) of food daily. Like the Sumatran rhino, it needs salt in its diet. The salt licks common in its historical range do not exist in Ujung Kulon, but the rhinos there have been observed drinking seawater, likely for the same nutritional need.

• published: 12 Apr 2015
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