Rhinoceros unicornis, Linnaeus, 1758

Don E. Wilson & Russell A. Mittermeier, 2011, Rhinocerotidae, Handbook of the Mammals of the World – Volume 2 Hoofed Mammals, Barcelona: Lynx Edicions, pp. 144-181 : 178-179

3.

Greater One-horned Rhinoceros

Rhinoceros unicornis

French: Rhinocéros indien / German: Panzernashorn / Spanish: Rinoceronte indio

Other common names: Indian Rhinoceros

Taxonomy. Rhinoceros unicornis Linnaeus, 1758 ,

India, Assam, Terai.

This species is monotypic.

Distribution. Nepal and India.

Descriptive notes. Head-body 335-346 cm, tail 66 cm, shoulder height 175— 200 cm; weight of adult males ¢. 2000 kg; females less. Few data exist on body mass of wild individuals. Males born in zoos are often more than 25 cm taller at the shoulder and considerably larger in mass than females. Like other perissodactyls, wild adult males and females show near monomorphism. Reduced size dimorphism in free-ranging animals may be explained by greater stress on males, and poor nutrition during the long non-breeding interval, when young adults are harassed by dominant males and excluded from prime grazing areas. Adult males develop longer mandibular incisors (tusks) and greater neck musculature than females. The lower outer incisors are 4-5 cm long, more than 3 cm at the base (females) and longer in males (if entire, 5:1.8-9 cm) or often broken. Long incisors (rather than horns), powerful neck and shoulder muscles, and extensive neck and shoulder skin folds figure prominently in fights and displays between breedingage males. The incisors are formidable offensive and defensive weapons, and are used rather than the horn in combat. Horn length averages 25 cm in adult males and 24 cm in adult females, but females often have longer (though slightly narrower) horns than the males that breed with them. Horn wear in adult males is common. This species has two distinct skin folds that drape over the sides of the front and hindlegs. Deep scars on anal folds, extra skin folds known as epidermal knobs, cuts on the ears, and missing tail tips allow for easy recognition of adults. Hair is limited to fringes ofears, eyelashes, and tail tip. Body color is gray and a mosaic-like pattern on the skin is quite noticeable on rump. Pedal scent glands are present.

Habitat. Greater One-horned Rhinos flourish in what are arguably the world’s tallest grasslands, in protected areas along the main river systems in the lowlands of the Himalayas. The rhinos generally avoid upland Shorea robusta forest, a dominant forest type, except during monsoon inundations, when these forests serve as temporary refugia. Oxbow lakes and other water features are important for wallowing and feeding on aquatic plants; this species is rarely found more than 2 km from water.

Food and Feeding. Greater One-horned Rhinos are primarily grazers, with the grass Saccharum spontaneum comprising a major part of the diet in all months of the year. During the winter months, rhinos browse much more frequently, as determined by fecal analysis and direct observation. In winter, scrub vegetation that is often found along the buffer zones on the edge of parks holds a particular attraction for the animals. They feed heavily on several browse species prevalent there, including Callicarpa macrophylla and Cassia tora. Even the stick-tight fruits and stems of the weedy Xanthium stromarium, an introduced weed normally dispersed on animal fur, are sought out by the rhino. Croplands attract rhinos and all of the other ungulates, and require nightly vigilance by farmers to scare animals away. Rhinos are partial to rice, corn, and wheat at ripening. They seek out and devour hot chilli plants, but feed only sparingly on the mustard crop. Most of their damage to crops occurs within a kilometer from park boundaries. Greater One-horned Rhinos ingested the fruits of at least 23 species of herbaceous and woody plants. Seeds manured into grassland latrines used by the rhinos yielded distinct assemblages of dicotyledonous plants. Trewia nudiflora, the most common riverine forest tree in Chitwan, and C. tora, an herb, accounted for most of the herbaceous cover. Although unattractive to arboreal and volant frugivores (monkeys, bats, and birds), Trewia fruit is an important food source for the rhino during the monsoon. The rhino plays an important role in dispersal and recruitment of woody species in riverine grasslands. Greater One-horned Rhinos have other profound effects on their landscape—they exert strong selective pressure on forest structure and canopy composition by inhibiting vertical growth of saplings, by frequent browsing and trampling.

Breeding. Males form dominance hierarchies. An alpha male’s tenure is short in comparison with his life span. The long mean interbirth interval (46 months), long gestation (16 months), and the presence of a small number of breeding age females in a population indicate that breeding opportunities are probably few for individual males. Limited chances for copulation probably heighten aggressive behavior when a female cycles into estrus. Non-breeding males seldom use prime grazing areas dominated by the grass S. spontaneum and occupied by dominant males. Dominant males attack young adult males if they remain in areas where breeding females concentrate. In contrast, females may occupy such areas even as subadults, and continue to occupy the maternal home range as adults. During fights to determine dominance, the males slash and gouge one another with the razor-sharp lower outer incisors, rather than relying on the horn. Three dominant males in Royal Chitwan National Park maintained their status with broken horns but intact incisors. No distinct season of parturition was detected based on births of 53 calves born during an intensive study conducted between 1984 and 1988 in which all breeding age females were photographed and monitored. Age at first reproduction for two known-age females was between 7-0 and 7-5 years. Interbirth intervals based on 13 females whose calves survived to independence were 45-6 + 1-8 months (range 34-51 months) Predation by Tigers (Panthera tigris) accounted for about 10% of calf mortality in one study where the two species overlapped. All calves killed by tigers were less than eight months old.

Activity patterns. It is a challenge for very large herbivores in subtropical or tropical habitats to find enough to eat and to stay cool during hot weather. Rhinos forage 47-54% of the 24hour cycle with distinct differences observed between sexes. Females are often pregnant or nursing. Adult males devote time to defending or patrolling areas where females congregate, so spend less time foraging. Rhinos feed both day and night. This species spends less time feeding than the other grazing rhino, the White Rhinoceros ( Ceratotherium simum ), perhaps because the grasses that account for the bulk ofits diet are much more abundant. Rhinos graze extensively during the day in the hottest, driest month of the year (April) and use wallows infrequently, counter to what might be predicted based on thermoregulatory behavior of other megaherbivores. Conversely, during hot, humid periods (monsoons), the rhinos spend much of the day in wallows, presumably to avoid heat stress. Several factors probably contribute to increased heat stress during the monsoon. The days are longer then, and thus total solar radiation is greater. Wind speed is also reduced, so that heat loss through evaporative cooling is less. Most importantly, the high humidity reduces the ability of large-bodied herbivores to use evaporative cooling to deal with heat stress. Wallowing behavior, which peaks in the monsoon, is correlated with changes in vapor pressure density, a measure of the ability of air to hold water vapor at different temperatures. Thus, the problem of heat stress, combined with easy access to preferred forage, probably restrict Greater One-horned Rhinos to riverine habitats during the monsoon.

Movements, Home range and Social organization. In prime habitat, adult females rarely travel more than 5 km during a 24hour period in any season. Adult breeding males travelled slightly longer distances during a 24hour period. Their movements were sufficient to allow them to cover most of their core areas of occupancy in a few days. Rarely does this species venture farther than 2 km from the river’s edge or another source of water. Translocated animals wandered over long distances (sometimes more than 25 km) before establishing a permanent home range. Home range data for radiocollared individuals revealed that Greater One-horned Rhinos may have the smallest annual and seasonal home ranges of any large herbivore. Annual home ranges of breeding females averaged 3-5 km?*; males’ ranges were only only 4-3 km®. The smallest home ranges were recorded for females during the monsoon, two females occupying core areas of only 22 ha and 28 ha, respectively. Females congregate in areas of excellent grass forage close to river banks. Males are notstrictly territorial, but form dominance hierarchies and attempt to defend areas where females congregate. Subadult males sometimes group together on the fringes of the best grazing areas. Adult males frequently fight, often resulting in serious injury and sometimes death.

Status and Conservation. CITES Appendix I. Classified as Vulnerable on The IUCN Red List. The Greater One-horned Rhino was once to be found right across the northern part of the Indian subcontinent,its range taking in the Indus, Ganges, and Brahmaputra river basins, and extending from Pakistan to the Indo-Burmese border, including parts of Nepal, Bangladesh, and Bhutan. It is also possible that it existed in Myanmar, southern China and Indochina, though this is unconfirmed. Common in north-western India and Pakistan up to about 1600, the species vanished from the region not long after that date. From 1600 to 1900 it suffered a sharp decline in numbers in the rest of its range, coming close to extinction at the start of the 20" century. The number of populations (13) and the total global population of this species (now approaching 2700 individuals) have climbed steadily over the past two decades. Intensive translocation efforts since 1984 and natural dispersal have expanded the western populations from the single source population, Chitwan, in Nepal, to two other reserves in western Nepal and three in India. Translocations from some of the smaller reserves in Assam and Bengal are also underway. Despite these accomplishments, only two populations currently contain more than 100 individuals, Kaziranga, with about 2000 rhinos, and Chitwan, with about 420. In some parts of the range, poaching has been intense. All of the 85 animals translocated to the Babai Valley in Bardia National Park were poached during the ten-year Maoist insurgency that ended in 2008. A small population remains in another part of Bardia and Sukla Phanta. Nevertheless, this species is much better off than the other two Asian species. Its recovery is still in question because populations occupy what could become prime agricultural habitat (floodplains), and the species still faces intense poaching pressure for its body parts. Nevertheless, the increases in Chitwan and Kaziranga and the establishment of new populations provide some of the best evidence that large, slow-breeding mammals can still undergo rapid expansion. This offers hope for the restoration of other endangered large mammals if they enjoy similar efforts at protection.

Bibliography. Amin et al. (2009), Anonymous (1909), Cooch Behar & Maharajah (1908), Dinerstein (1991a, 1991b, 1992, 2003), Dinerstein & Gyawali (1993), Dinerstein & McCracken (1990), Dinerstein & Price (1991), Dinerstein & Wemmer (1988), Dinerstein, Rijal et al. (1999), Dinerstein, Shrestha & Mishra (1990), Foose & van Strien (1997), Gee (1953), Gyawali (1986), IUCN (1994), Laurie (1978, 1982), Laurie et al. (1983), Martin & Vigne (1995), Menon (1996), Olson & Dinerstein (1998), Owen-Smith (1988), Prothero & Schoch (1989), Seidensticker (1976), Syangden et al. (2008), Wikramanayake & Dinerstein (1998), Yonzon (1994).

Figures

1. White Rhinoceros (Ceratotherium simum), 2. Black Rhinoceros (Diceros bicornis), 3. Greater One-horned Rhinoceros (Rhinoceros unicornis), 4. Javan Rhinoceros (Rhinoceros sondaicus), 5. Sumatran Rhinoceros (Dicerorhinus sumatrensis)

Distribution. Nepal and India .