The Javan rhinoceros (Rhinoceros sondaicus), also called Javan rhino, Sunda rhinoceros and lesser one-horned rhinoceros is a critically endangered member of the genus Rhinoceros of the family Rhinocerotidae, and one of the five remaining extant rhinoceros species. It has a plate-like skin with protective folds and is one of the smallest rhinoceros species with a body length of and a long tail. The heaviest specimens weigh around . Its horn is usually shorter than .
Until the mid-19th to about the early 20th century, the Javan rhinoceros had ranged beyond the islands of Java and Sumatra and onto the mainland of Southeast Asia and Indochina, northwest into East India, Bhutan, and the south of China. Today, it is the rarest of all rhinoceroses, and among the rarest of all living animal species, with only one currently known wild population, and no individuals successfully kept in captivity. It is among the rarest large mammals in the world with a population around 74 within Ujung Kulon National Park, at the far western tip of Java, Indonesia.
The decline of the Javan rhinoceros is primarily attributed to poaching for the males' horns, which are highly valued in traditional Chinese medicine, fetching as much as US$30,000 per kg on the black market. As the presence of colonial Dutch and other Europeans in its range increased, peaking in the 1700–1800s, trophy hunting also became a serious threat. Loss of habitat and massive human population growth especially postwar times have also contributed to its decline and hindered the species' recovery. The remaining range is within one nationally protected area, and Ujung Kulon is also a UNESCO World Heritage Site. Nonetheless, rural, potentially rugged park boundaries mean that law enforcement cannot be equally present in all places at all times; in some areas, this lack of security still places the species at risk from poachers, disease exposure, and ultimately loss of genetic diversity, leading to genetic "bottlenecking" (i.e., inbreeding depression).
The Javan rhinoceros can live around 30–45 years in the wild. It historically inhabited dense lowland rainforest, wet grasslands, and vast floodplains at forest edges. It is mostly solitary, except for courtship and rearing offspring, though groups may occasionally congregate near wallows and salt licks. Aside from humans, whom they usually avoid, adults have no natural predators in their range. Very small juveniles may be preyed upon, if left unsupervised, typically by Javan leopards, the now extinct Javan tiger, or rarely saltwater crocodiles. Scientists and conservationists rarely study the animals directly due to their extreme rarity and the danger of interfering with such an endangered species. Researchers instead rely on camera traps and fecal samples to gauge health and behavior. Consequently, Javan rhinos are the least-studied of all rhinoceros species. Two adult female Javan rhinoceroses, each with a calf, were filmed using a motion-triggered trail camera, the video being released on 28 February 2011 by WWF and Indonesia's National Park Authority, proving they are still breeding in the wild.
Etymology The generic name Rhinoceros is a combination of the ancient Greek words ῥίς (ris) meaning nose and κέρας (keras) meaning horn of an animal. The specific name sondaicus is derived from sunda, the biogeographical region that comprises the islands of Sumatra, Java, Borneo, and surrounding smaller islands. The Javan rhino is also known as the lesser one-horned rhinoceros (in contrast with the greater one-horned rhinoceros, another name for the Indian rhino).
Taxonomy Rhinoceros sondaicus was the scientific name used by Anselme Gaëtan Desmarest in 1822 for a rhinoceros from Java sent by Pierre-Médard Diard and Alfred Duvaucel to the National Museum of Natural History, France. In the 19th century, several zoological specimens of hornless rhinoceroses were described: Rhinoceros inermis proposed by René Lesson in 1838 was a female rhinoceros without horns shot in the Sundarbans. Rhinoceros nasalis and Rhinoceros floweri proposed by John Edward Gray in 1867 were two rhinoceros skulls from Borneo and one from Sumatra, respectively. Rhinoceros annamiticus proposed by Pierre Marie Heude in 1892 was a specimen from Vietnam.
As of 2005, three Javan rhinoceros subspecies are considered valid taxa: R. s. sondaicus, the nominate subspecies, known as the Indonesian Javan rhinoceros R. s. inermis, known as the Indian Javan rhinoceros or lesser Indian rhinoceros R. s. annamiticus, known as the Vietnamese Javan rhinoceros or Vietnamese rhinoceros
Evolution
Ancestral rhinoceroses are held to have first diverged from other perissodactyls in the Early Eocene. Mitochondrial DNA comparison suggests the ancestors of modern rhinos split from the ancestors of the Equidae around 50 million years ago (Mya). The extant family, the Rhinocerotidae, first appeared in the Late Eocene in Eurasia, and the ancestors of the extant rhino species dispersed from Asia beginning in the Miocene.
The last common ancestor of living rhinoceroses belonging to the subfamily Rhinocerotinae is suggested to have lived around 16 Mya, with the ancestors of the genus Rhinoceros diverging from the ancestors of other living rhinoceroses around 15 Mya. The genus Rhinoceros has been found to be overall slightly more closely related to the Sumatran rhinoceros (as well as to the extinct woolly rhinoceros and the extinct Eurasian genus Stephanorhinus) than to living African rhinoceroses, though gene flow appears to have occurred between the ancestors of living African rhinoceroses and the genus Rhinoceros, as well as between the ancestors of the genus Rhinoceros and the ancestors of the woolly rhinoceros and Stephanorhinus.
A cladogram showing the relationships of recent and Late Pleistocene rhinoceros species (minus Stephanorhinus hemitoechus) based on whole nuclear genomes
The oldest known definitive fossils of the Javan rhinoceros are from the Late Pliocene deposits of Myanmar, Java, and Pakistan. Molecular estimates suggest the Indian and Javan rhinoceros diverged from each other earlier, around 4.3 million years ago. An astragalus fossil similar to that of the Javan rhinoceros from the Late Miocene deposits of Myanmar have been identified as Rhinoceros cf. R. sondaicus.
Description
Javan rhinos are smaller than the Indian rhinoceros, and are close in size to the black rhinoceros. They are the largest animal in Java and the second-largest animal in Indonesia after the Asian elephant. The length of a Javan rhino including its head is , and it can reach a height of . Adults are variously reported to weigh between , although a study to collect accurate measurements of the animals has never been conducted and is not a priority because of their extreme conservation status. No substantial size difference is seen between genders, but cows may be slightly bigger. The rhinos in Vietnam appeared to be significantly smaller than those in Java, based on studies of photographic evidence and measurements of their footprints.
Like the Indian rhino, the Javan rhino has a single horn (the other extant species have two horns). Its horn is the smallest of all extant rhinos, usually less than with the longest recorded only . Only bulls have horns. Cows are the only extant rhinos that remain hornless into adulthood, though they may develop a tiny bump of an inch or two in height. Javan rhinos do not appear to often use their horns for fighting, but instead use them to scrape mud away in wallows, to pull down plants for eating, and to open paths through thick vegetation. Similar to the other browsing species of rhino (black and Sumatran), the Javan rhino has a long, pointed, upper lip, which helps in grabbing food. The lower incisors are long and sharp; when Javan rhinos fight, they use these teeth. Behind the incisors, two rows of six low-crowned molars are used for chewing coarse plants. Like all rhinos, Javan rhinos smell and hear well, but have very poor vision. They are estimated to live for 30 to 45 years.
Their hairless, splotchy gray, or gray-brown skin falls in folds to the shoulder, back, and rump. The skin has a natural mosaic pattern, which lends the rhino an armored appearance. The neck folds of Javan rhinoceros are smaller than those of the Indian rhinoceros, but still form a saddle shape over the shoulders. Because of the risks of interfering with such an endangered species, however, Javan rhinos are primarily studied through fecal sampling and camera traps. They are rarely encountered, observed, or measured directly.
Distribution and habitat
Fossil remains of Javan rhinoceros have been found at the Neolithic site of Hemudu in Zhejiang, China, and the 4th century BCE Classic of Mountains and Seas appears to describe one living in the Yangtze River basin. Remains were also found in the Tam Hay Marklot cave site in northeastern Laos that date to the Pleistocene.
Historically, Javan rhinoceroses were widespread from Assam and Bengal, eastward to Myanmar, Thailand, Cambodia, Laos, Vietnam, and southwards to the Malay Peninsula and the islands of Sumatra, Java, and Borneo. Today, the species only occurs in Ujung Kulon National Park in southwestern Java, where fewer than 100 individuals are estimated to survive.
The range of the Javan rhinoceros has been shrinking for at least 3,000 years. Starting around 1000 BC, the northern range of the rhinoceros extended into China, but began moving southward at roughly per year, as human settlements increased in the region. It likely became locally extinct in India in the first decade of the 20th century. The Javan rhino was hunted to extinction on the Malay Peninsula by 1932. The last ones on Sumatra are thought to have died during World War II; it may have also been present on Borneo, but these specimens could have been Sumatran rhinocerosses, a small population which still lives there.
The Javan rhinoceros was sighted in the Sunderbans between 1630 and 1908, but only six were thought to have survived by 1892.
By the end of the Vietnam War, the Vietnamese rhinoceros was thought extinct across all of mainland Asia. Local hunters and woodcutters in Cambodia claim to have seen Javan rhinos in the Cardamom Mountains, but surveys of the area have failed to find any evidence. In the late 1980s, a small population was found in the Cat Tien area of Vietnam, but the last known individual of that population was shot in 2010. The population in Vietnam's Cat Tien National Park was declared locally extinct in 2011.
The Javan rhinoceros primarily inhabits dense, lowland rain forests, grasslands, and reed beds with abundant rivers, large floodplains, or wet areas with many mud wallows. Although it historically preferred low-lying areas, the subspecies in Vietnam was pushed onto much higher ground (up to 2,000 m or 6,561 ft), probably because of human encroachment and poaching.
Behavior and ecology
The Javan rhinoceros is a solitary animal with the exception of breeding pairs and mothers with calves. They 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 Javan rhinoceros does not generally dig its own mud wallows, preferring to use other animals' wallows or naturally occurring pits, which it uses its horn to enlarge. Salt licks are also very important because of the essential nutrients the rhino receives from the salt. Bull home ranges are larger at compared to the cow, which are around . Bull territories overlap each other less than those of the cow. Whether territorial fights occur is unknown.