The Indian Rhinoceros (Rhinoceros unicornis) is also called Greater One-horned Rhinoceros and Asian One-horned Rhinoceros and belongs to the Rhinocerotidae family. Listed as a vulnerable species, the large mammal is primarily found in parts of north-eastern India and in protected areas in the Terai of Nepal, where populations are confined to the riverine grasslands in the foothills of the Himalayas. Weighing between 2260 kg and 3000 kg, it is the fourth largest land animal and has a single horn, which measures 20 cm to 57 cm in length.
These Rhinoceros once ranged throughout the entire stretch of the Indo-Gangetic Plain but excessive hunting reduced their natural habitat drastically. Today, about 3,000 Rhinos live in the wild, 2000 of which are found in Assam’s Kaziranga alone. These Rhinoceros can run at speeds of up to 55 km/h (34 mph) for short periods of time and is also an excellent swimmer. It has excellent senses of hearing and smell but relatively poor eyesight.
In size, the Indian Rhinoceros is equal to that of the white rhino in Africa; together they are the largest of all rhino species. Fully grown males are larger than females in the wild, weighing from 2,200 to 3,000 kg (4,900 to 6,600 lb). Female Indian rhinos weigh about 1,600 kg. The Indian Rhino is from 1.7 to 2 m (5 ft 7 in to 6 ft 7 in) tall and can be up to 4 m (13 ft) long. The record-sized specimen of this rhino was approximately 3,500 kg.
The Indian rhinoceros has a single horn; this is present in both males and females, but not on newborn young. The horn, like human fingernails, is pure keratin and starts to show after about 6 years. In most adults the horn reaches a length of about 25 centimeters, but has been recorded up to 57.2 centimeters in length. The nasal horn curves backwards from the nose. Its horn is naturally black. In captive animals, the horn is frequently worn down to a thick knob.
This prehistoric-looking rhinoceros has thick, silver-brown skin which becomes pinkish near the large skin folds that cover its body. Males develop thick neck-folds. Its upper legs and shoulders are covered in wart-like bumps. It has very little body hair, aside from eyelashes, ear-fringes and tail-brush.
In captivity, four are known to have lived over 40 years, the oldest living to be 47.
These rhinos live in tall grasslands and riverine forests but due to habitat loss they have been forced into more cultivated land. They are mostly solitary creatures, with the exception of mothers and calves and breeding pairs, although they sometimes congregate at bathing areas. They have home ranges, the home ranges of males being usually 2-8 square kilometers in size, and overlapping each other. Dominant males tolerate males passing through their territory except when they are in mating season, when dangerous fights break out. They are active at night and early morning. They spend the middle of the day wallowing in lakes, rivers, ponds, and puddles to cool down. They are extremely good swimmers.
Indian rhinos have few natural enemies, except for tigers. Tigers sometimes kill unguarded calves, but adult rhinos are less vulnerable due to their size. Humans are the only other animal threat, hunting the rhinoceros primarily for sport or for the use of its horn. Mynahs and egrets both eat invertebrates from the rhino's skin and around its feet. Tabanus flies, a type of horse-fly are known to bite rhinos. The rhinos are also vulnerable to diseases spread by parasites such as leeches, ticks, and nematodes. Anthrax and the blood-disease septicemia are known to occur.
The Indian Rhinoceros is a grazer. Their diet consists almost entirely of grasses, but the rhino is also known to eat leaves, branches of shrubs and trees, fruits and submerged and floating aquatic plants.
Feeding occurs during the morning and evening. The rhino uses its prehensile lip to grasp grass stems, bend the stem down, bite off the top, and then eat the grass. With very tall grasses or saplings, the rhino will often walk over the plant, with its legs on both sides, using the weight of its body to push the end of the plant down to the level of the mouth. Mothers also use this technique to make food edible for their calves. They drink for a minute or two at a time, often imbibing water filled with rhinoceros urine.
The Indian Rhinoceros forms a variety of social groupings. Adult males are generally solitary, except for mating and fighting. Adult females are largely solitary when they are without calves. Mothers will stay close to their calves for up to four years after their birth, sometimes allowing an older calf to continue to accompany her once a newborn calf arrives. Sub-adult males and females form consistent groupings as well. Groups of two or three young males will often form on the edge of the home ranges of dominant males, presumably for protection in numbers. Young females are slightly less social than the males. Indian Rhinos also form short-term groupings, particularly at forest wallows during the monsoon season and in grasslands during March and April. Groups of up to 10 rhinos may gather in wallows—typically a dominant male with females and calves, but no subadult males.
The one horned Indian Rhinoceros makes a wide variety of vocalizations. At least ten distinct vocalizations have been identified: snorting, honking, bleating, roaring, squeak-panting, moo-grunting, shrieking, groaning, rumbling and humphing. In addition to noises, the rhino uses olfactory communication. Adult males urinate backwards, as far as 3–4 meters behind them, often in response to being disturbed by observers. Like all rhinos, the Indian Rhinoceros often defecates near other large dung piles. The Indian Rhino has pedal scent glands which are used to mark their presence at these rhino latrines. Males have been observed walking with their heads to the ground as if sniffing, presumably following the scent of females.
In aggregations, Indian Rhinos are often friendly. They will often greet each other by waving or bobbing their heads, mounting flanks, nuzzling noses, or licking. Rhinos will playfully spar, run around, and play with twigs in their mouth. Adult males are the primary instigators in fights. Fights between dominant males are the most common cause of rhino mortality and males are also very aggressive toward females during courtship. Males will chase females over long distances and even attack them face-to-face. Unlike African Rhinos, the Indian Rhino fights with its incisors, rather than its horns.