|Range||India, Bhutan, Bangladesh, Myanmar, Laos, Thailand, Malaysia, Indonesia, and China|
The Sumatran rhinoceros, (Dicerorhinus sumatrensis) is a member of the family Rhinocerotidae and one of five extant rhinoceroses. of the genus Dicerorhinus. It is the smallest rhinoceros, although it is still a large mammal. This rhino stands 112–145 cm (3.67–4.76 ft) high at the shoulder, with a head-and-body length of 2.36–3.18 m (7.7–10.4 ft) and a tail of 35–70 cm (14–28 in). The weight is reported to range from 500 to 1,000 kg (1,100 to 2,200 lb), averaging 700–800 kg (1,500–1,800 lb), although there is a single record of a 2,000 kg (4,400 lb) specimen. Like both African species, it has two horns; the larger is the nasal horn, typically 15–25 cm (5.9–9.8 in), while the other horn is typically a stub. A coat of reddish-brown hair covers most of the Sumatran rhino's body.
Members of the species once inhabited rainforests, swamps, and cloud forests in India, Bhutan, Bangladesh, Myanmar, Laos, Thailand, Malaysia, Indonesia, and China. In historical times, they lived in southwest China, particularly in Sichuan. They are now critically endangered, with only six substantial populations in the wild: four on Sumatra, one on Borneo, and one in the Malay Peninsula. Their numbers are difficult to determine because they are solitary animals that are widely scattered across their range, but they are estimated to number fewer than 275. Survival of the Peninsular Malaysia population is in doubt, and one of the Sumatran populations may already be extinct. Total numbers today may be as low as 200. The decline in the number of Sumatran rhinoceroses is attributed primarily to poaching for their horns, which are highly valued in traditional Chinese medicine, fetching as much as US$30,000 per kg on the black market.
The Sumatran rhino is a mostly solitary animal except for courtship and offspring-rearing. It is the most vocal rhino species and also communicates through marking soil with its feet, twisting saplings into patterns, and leaving excrement. The species is much better studied than the similarly reclusive javan rhinoceros, in part because of a program that brought 40 Sumatran rhinos into captivity with the goal of preserving the species. The program was considered a disaster even by its initiator; most of the rhinos died and no offspring were produced for nearly 20 years, representing an even worse population decline than in the wild.
Taxonomy and Naming
Ancestral rhinoceroses first diverged from other perissodactyls in the Early Eocene. Mitochondrial DNA comparison suggests the ancestors of modern rhinos split from the ancestors of Equidae around 50 million years ago. 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 Sumatran rhinoceros is considered the least derived of the extant species, as it shares more traits with its Miocene ancestors. Paleontological evidence in the fossil record dates the genus Dicerorhinus to the Early Miocene, 23–16 million years ago. Many fossils have been classified as members of Dicerorhinus, but no other recent species are in the genus. Molecular dating suggests a split of Dicerorhinus from the four other extant species as far back as 25.9 ± 1.9 million years. Three hypotheses have been proposed for the relationship between the Sumatran rhinoceros and the other living species. One hypothesis suggests the Sumatran rhinoceros is closely related to the black and white rhinos in Africa, evidenced by the species having two horns, instead of one. Other taxonomists regard the Sumatran rhinoceros as a sister taxon of the Indian and Javan rhinoceros because their ranges overlap so closely. A third hypothesis, based on more recent analyses, however, suggests the two African rhinos, the two Asian rhinos, and the Sumatran rhinoceros represent three essentially separate lineages that split around 25.9 million years ago, and which group diverged first remains unclear.
Because of morphological similarities, the Sumatran rhinoceros is believed to be closely related to the extinct woolly rhinoceros, The woolly rhinoceros, so named for the coat of hair it shares with the Sumatran rhinoceros, first appeared in China; by the Upper Pleistocene, it ranged across the Eurasian continent from Korea to Spain. The woolly rhinoceros survived the last Ice Age, but like the woolly mammoth, most or all became extinct around 10,000 years ago. Although some morphological studies questioned the relationship, recent molecular analysis has supported the two species as sister taxa.
A mature Sumatran rhino stands about 120–145 cm (3.9–4.76 ft) high at the shoulder, has a body length of around 250 cm (8.2 ft) and weighs 500–800 kg (1,100–1,800 lb), hough the largest individuals in zoos have been known to weigh as much as 2,000 kilograms (4,400 lb). Like the African species, it has two horns. The larger is the nasal horn, typically only 15–25 cm (5.9–9.8 in), though the longest recorded specimen was much longer at 81 cm (32 in). The posterior horn is much smaller, usually less than 10 cm (3.9 in) long, and often little more than a knob. The larger nasal horn is also known as the anterior horn; the smaller posterior horn as the frontal horn. The horns are dark grey or black in color. The males have larger horns than the females, though the species is not otherwise sexually dimorphic. The Sumatran rhino lives an estimated 30–45 years in the wild, while the record time in captivity is a female sumatran rhinoceros which lived for 32 years and 8 months before dying in the London Zoo in 1900.
Two thick folds of skin encircle the body behind the front legs and before the hind legs. The rhino has a smaller fold of skin around its neck. The skin itself is thin, 10–16 mm (0.39–0.63 in), and in the wild, the rhino appears to have no subcutaneous fat. Hair can range from dense (the most dense hair in young calves) to scarce, and is usually a reddish-brown. In the wild, this hair is hard to observe because the rhinos are often covered in mud. In captivity, however, the hair grows out and becomes much shaggier, likely because of less abrasion from walking through vegetation. The rhino has a patch of long hair around its ears and a thick clump of hair at the end of its tail. Like all rhinos, they have very poor vision. The Sumatran rhinoceros is fast and agile; it climbs mountains easily and comfortably traverses steep slopes and riverbanks.
Distribution and Habitat
The Sumatran rhinoceros lives in both lowland and highland secondary rainforest, swamps, and cloud forests. It inhabits hilly areas close to water, particularly steep upper valleys with copious undergrowth. The Sumatran rhinoceros once inhabited a continuous range as far north as Burma, eastern India, and Bangladesh. Unconfirmed reports also placed it in Cambodia, Laos, and Vietnam. All known living animals occur in Peninsular Malaysia, the island of Sumatra, and Sabah, Borneo. Some conservationists hope Sumatran rhinos may still survive in Burma, though it is considered unlikely. Political turmoil in Burma has prevented any assessment or study of possible survivors. The last reports of stray animals from Indian limits were in 1990s.
Sumatran rhinoceroses are solitary creatures except for pairing before mating and during offspring rearing. Individuals have home ranges; bulls have territories as large as 50 km2 (19 sq mi), whereas females' ranges are 10–15 km2 (3.9–5.8 sq mi). The ranges of females appear to be spaced apart; males' ranges often overlap. No evidence indicates Sumatran rhinos defend their territories through fighting. Marking their territories is done by scraping soil with their feet, bending saplings into distinctive patterns, and leaving excrement. The Sumatran rhino is usually most active when eating, at dawn, and just after dusk. During the day, they wallow in mud baths to cool down and rest. In the rainy season, they move to higher elevations; in the cooler months, they return to lower areas in their range. When mud holes are unavailable, the rhino will deepen puddles with its feet and horns. The wallowing behaviour helps the rhino maintain its body temperature and protect its skin from ectoparasites and other insects. Captive specimens, deprived of adequate wallowing, have quickly developed broken and inflamed skins, suppurations, eye problems, inflamed nails, and hair loss, and have eventually died. One 20-month study of wallowing behavior found they will visit no more than three wallows at any given time. After two to 12 weeks using a particular wallow, the rhino will abandon it. Typically, the rhino will wallow around midday for two to three hours at a time before venturing out for food. Although in zoos the Sumatran rhino has been observed wallowing less than 45 minutes a day, the study of wild animals found 80–300 minutes (an average of 166 minutes) per day spent in wallows.
There has been little opportunity to study epidemiology in the Sumatran rhinoceros. ticks and gyrostigma were reported to cause deaths in captive animals in the 19th century. The rhino is also known to be vulnerable to the blood disease surra, which can be spread by horse-flies carrying parasitic trypanosomes; in 2004, all five rhinos at the Sumatran Rhinoceros Conservation Centre died over an 18-day period after becoming infected by the disease. The Sumatran rhino has no known predators other than humans. Tigers and wild dogs may be capable of killing a calf, but calves stay close to their mothers, and the frequency of such killings is unknown. Although the rhino's range overlaps with asian elephants and malayan tapirs, the species do not appear to compete for food or habitat. Asian Elephants and sumatran rhinos are even known to share trails, and many smaller species such as deer, wild boars, and wild dogs will use the trails the rhinos and elephants create.
The Sumatran rhino maintains trails across its range. The trails fall into two types. Main trails will be used by generations of rhinos to travel between important areas in the rhino's range, such as between salt licks, or in corridors through inhospitable terrain that separates ranges. In feeding areas, the rhinos will make smaller trails, still covered by vegetation, to areas containing food the rhino eats. Sumatran rhino trails have been found that cross rivers deeper than 1.5 m (5 ft) and about 50 m (165 ft) across. The currents of these rivers are known to be strong, but the rhino is a strong swimmer. A relative absence of wallows near rivers in the range of the Sumatran rhinoceros indicates they may occasionally bathe in rivers in lieu of wallowing.
Most feeding occurs just before nightfall and in the morning. The Sumatran rhino is a browser, with a diet of young saplings, leaves, fruits, twigs, and shoots. The rhinos usually consume up to 50 kg (110 lb) of food a day. Primarily by measuring dung samples, researchers have identified more than 100 food species consumed by the Sumatran rhinoceros. The largest portion of the diet is tree saplings with a trunk diameter of 1–6 cm (0.4–2.4 in). The rhinoceros typically pushes these saplings over with its body, walking over the sapling without stepping on it, to eat the leaves. Many of the plant species the rhino consumes exist in only small portions, which indicates the rhino is frequently changing its diet and feeding in different locations. Among the most common plants the rhino eats are many species from the Euphorbiaceae, Rubiaceae, Melastomataceae families. The most common species the rhino consumes is Eugenia.
The vegetal diet of the Sumatran rhinoceros is high in fiber and only moderate in protein. Salt licks are very important to the nutrition of the rhino. These licks can be small hot springs, seepages of salty water, or mud-volcanoes. The salt licks also serve an important social purpose for the rhinos—males visit the licks to pick up the scent of females in oestrus. Some Sumatran rhinos, however, live in areas where salt licks are not readily available, or the rhinos have not been observed using the licks. These rhinos may get their necessary mineral requirements by consuming plants rich in minerals.
The Sumatran rhinoceros is the most vocal of the rhinoceros species. Observations of the species in zoos show the animal almost constantly vocalizing, and it is known to do so in the wild, as well. The rhino makes three distinct noises: eeps, whales, and whistle-blows. The eep, a short, one-second-long yelp, is the most common sound. The whale, named for its similarity to vocalizations of the humpback whale, is the most song-like vocalization and the second-most common. The whale varies in pitch and lasts from four to seven seconds. The whistle-blow is named because it consists of a two-second-long whistling noise and a burst of air in immediate succession. The whistle-blow is the loudest of the vocalizations, loud enough to make the iron bars in the zoo enclosure where the rhinos were studied vibrate. The purpose of the vocalizations is unknown, though they are theorized to convey danger, sexual readiness, and location, as do other ungulate vocalizations. The whistle-blow could be heard at a great distance, even in the dense brush in which the Sumatran rhino lives. A vocalization of similar volume from elephants has been shown to carry 9.8 km (6.1 mi) and the whistle-blow may carry as far. The Sumatran rhinoceros will sometimes twist the saplings they do not eat. This twisting behavior is believed to be used as a form of communication, frequently indicating a junction in a trail.
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Females become sexually mature at the age of six to seven years, while males become sexually mature at about 10 years old. The gestation period is around 15–16 months. The calf, which typically weighs 40–60 kg (88–132 lb), is weaned after about 15 months and stays with its mother for the first two to three years of its life. In the wild, the birth interval for this species is estimated to be four to five years; its natural offspring-rearing behavior is unstudied.
The reproductive habits of the Sumatran rhinoceros have been studied in captivity. Sexual relationships begin with a courtship period characterized by increased vocalization, tail raising, urination, and increased physical contact, with both male and female using their snouts to bump the other in the head and genitals. The pattern of courtship is most similar to that of the black rhinoceros. Young Sumatran rhino males are often too aggressive with females, sometimes injuring and even killing them during the courtship. In the wild, the female could run away from an overly aggressive male, but in their smaller captive enclosures, they cannot; this inability to escape aggressive males may partly contribute to the low success rate of captive-breeding programs.
The period of oestrus itself, when the female is receptive to the male, lasts about 24 hours, and observations have placed its recurrence between 21 an 25 days. Rhinos in the Cincinnati Zoo have been observed copulating for 30–50 minutes, similar in length to other rhinos; observations at the Sumatran Rhinoceros Conservation Centre in Malaysia have shown a briefer copulation cycle. As the Cincinnati Zoo has had successful pregnancies, and other rhinos also have lengthy copulatory periods, a lengthy rut may be the natural behavior. Though researchers observed successful conceptions, all these pregnancies ended in failure for a variety of reasons until the first successful captive birth in 2001; studies of these failures at the Cincinnati Zoo discovered the Sumatran rhino's ovulation is induced by mating and it had unpredictable progesterone levels. Breeding success was finally achieved in 2001, 2004, and 2007 by providing a pregnant rhino with supplementary progestin. Recently, a calf was born in captivity of an endangered female in western Indonesia, only the fifth such birth in one and a quarter century.
Sumatran rhinoceroses were once quite numerous throughout Southeast Asia. Fewer than 275 individuals are now estimated to remain.
Though rare, Sumatran rhinoceroses have occasionally been exhibited in zoos for nearly a century and a half. The London Zoo acquired two Sumatran rhinoceros in 1872. One of these, a female named "Begum", was captured in Chittagong in 1868 and survived at the London Zoo until 1900, the record lifetime in captivity for a Sumatran rhino. Begum was also the type of the extinct subspecies D. s. lasiotis. At the time of their acquisition, Philip Sclater, the secretary of the Zoological Society of London, claimed the first Sumatran rhinoceros in zoos had been in the collection of the Zoological Garden of Hamburg since 1868. Before the extinction of the subspecies Dicerorhinus sumatrensis lasiotis, at least seven specimens were held in zoos and circuses. Sumatran rhinos, however, did not thrive outside their native habitats. A rhino in the Calcutta Zoo successfully gave birth in 1889, but for the entire 20th century, not one Sumatran rhino was born in a zoo. In 1972, Subur, the only Sumatran rhino remaining in captivity, died at the Copenhagen Zoo.
Despite the species' persistent lack of reproductive success, in the early 1980s, some conservation organizations began a captive-breeding program for the Sumatran rhinoceros. Between 1984 and 1996, this ex situ conservation program transported 40 Sumatran rhinos from their native habitats to zoos and reserves across the world. While hopes were initially high, and much research was conducted on the captive specimens, by the late 1990s, not a single rhino had been born in the program, and most of its proponents agreed the program had been a failure. In 1997, the IUCN's Asian rhino specialist group, which once endorsed the program, declared it had failed "even maintaining the species within acceptable limits of mortality", noting that, in addition to the lack of births, 20 of the captured rhinos had died. In 2004, a surra outbreak at the Sumatran Rhinoceros Conservation Centre killed all the captive rhinos in Peninsular Malaysia, reducing the population of captive rhinos to eight.
Seven of these captive rhinos were sent to the United States (the other was kept in Southeast Asia), but by 1997, their numbers had dwindled to three: a female in the Los Angeles Zoo, a male in the Cincinnati Zoo, and a female in the Bronx Zoo. In a final effort, the three rhinos were united in Cincinnati. After years of failed attempts, the female from Los Angeles, Emi, became pregnant for the sixth time, with the zoo's male Ipuh. All five of her previous pregnancies ended in failure. Researchers at the zoo had learned from previous failures, though, and with the aid of special hormone treatments, Emi gave birth to a healthy male calf named Andalas (an Indonesian literary word for Sumatra) in September 2001. Andalas's birth was the first successful captive birth of a Sumatran rhino in 112 years. A female calf, named "Suci" (Indonesian for "pure"), followed on July 30, 2004. On April 29, 2007, Emi gave birth a third time, to her second male calf, named Harapan (Indonesian for "hope") or Harry. In 2007, Andalas, who had been living at the Los Angeles Zoo, was returned to Sumatra to take part in breeding programs with healthy females, leading to the siring and June 23, 2012 birth of male calf Andatu, the fourth captive-born calf of the era; Andalas had been mated with Ratu, a wild-born female living in the Rhino Sanctuary at Way Kambas National Park.
Despite the recent successes in Cincinnati, the captive-breeding program has remained controversial. Proponents argue the zoos have aided the conservation effort by studying the reproductive habits, raising public awareness and education about the rhinos, and helping raise financial resources for conservation efforts in Sumatra. Opponents of the captive breeding program argue the losses are too great; the program is too expensive; removing rhinos from their habitat, even temporarily, alters their ecological role; and captive populations cannot match the rate of recovery seen in well-protected native habitats.