The Indian Rhinoceros, scientifically known as Rhinoceros unicornis, is a notable species native to the Indian subcontinent. Also referred to as the greater one-horned rhinoceros or simply the Indian rhino, it ranks as the second largest living rhinoceros species. Adult males typically weigh between 2.07 to 2.2 tonnes, while females weigh around 1.6 tonnes. These rhinos possess thick, grey-brown skin with pinkish folds. A distinguishing feature is the single horn on their snout, which can grow up to 57.2 cm (22.5 in). Wart-like bumps cover their upper legs and shoulders, and they are mostly hairless except for eyelashes, ear fringes, and a tail brush.

Physical Characteristics of Indian Rhinoceros
Indian rhinoceroses boast a thick grey-brown skin adorned with pinkish folds and a single horn on their snout. Their upper legs and shoulders are characterized by wart-like bumps, while they possess minimal body hair, except for eyelashes, ear fringes, and a tail brush. Bulls exhibit significant neck folds.

The skull of Indian rhinos is substantial, with a basal length exceeding 60 cm and an occiput over 19 cm. Their nasal horn, slightly back-curved, has a base measuring approximately 18.5 cm by 12 cm, tapering rapidly until a smooth, even stem part begins about 55 mm above the base. In captivity, the horn often wears down to a thick knob. Both male and female Indian rhinos possess a single horn, absent in newborn calves. Composed of pure keratin, akin to human fingernails, the horn typically emerges around six years of age. In adults, the horn typically reaches about 25 cm in length, although lengths of up to 57.2 cm and weights of 3.051 kg have been recorded.

Among terrestrial land mammals native to Asia, Indian rhinos rank second in size only to the Asian elephant and are the second-largest living rhinoceros species, behind only the white rhinoceros. Bulls typically measure 368–380 cm in head and body length, with a shoulder height of 163–193 cm, while cows measure 310–340 cm in head and body length, with a shoulder height of 147–173 cm. Bulls weigh on average about 2,070–2,200 kg, heavier than cows, which average about 1,600 kg.

The pinkish hue of the skin is due to the rich presence of blood vessels underneath the tissues in folds. These folds serve to increase the surface area and aid in regulating body temperature. Despite the thick skin, Indian rhinos are vulnerable to bloodsucking Tabanus flies, leeches, and ticks. Reports suggest that the largest individuals may weigh up to 4,000 kg.

Distribution in India
The Indian rhinoceros, historically, occupied the northern regions of the Indian subcontinent, along the basins of the Indus, Ganges, and Brahmaputra rivers. Its habitat primarily consisted of the alluvial grasslands of the Terai and the Brahmaputra basin. However, due to habitat destruction and climatic changes, its range gradually diminished. By the 19th century, it was only found in the Terai grasslands of southern Nepal, northern Uttar Pradesh, northern Bihar, northern West Bengal, and the Brahmaputra Valley of Assam.

In modern times, the range of the Indian rhinoceros has further contracted to a few isolated areas in southern Nepal, northern West Bengal, and the Brahmaputra Valley. Its habitat is now surrounded by human-dominated landscapes, leading to its presence in cultivated areas, pastures, and secondary forests in many regions. In the 1980s, Indian rhinos were frequently observed in the narrow plain area of the Manas River and the Royal Manas National Park in Bhutan.

As of 2022, the total population of Indian rhinoceroses was estimated at 4,014 individuals, showing an increase from 2,577 individuals recorded in 2006. Of these, 3,262 are located in India, while the remaining 752 are distributed across Nepal and Bhutan. Bhutan does not have a permanent rhino population, but occasional sightings occur as small rhino groups cross from the Manas National Park or Buxa Tiger Reserve in India.

In India, Assam harbors the largest population, with approximately 2,885 individuals. This includes 2,613 in Kaziranga National Park, 125 in Orang National Park, 107 in Pobitora Wildlife Sanctuary, and 40 in Manas National Park. West Bengal hosts 339 individuals, with 287 in Jaldapara National Park and 52 in Gorumara National Park. Dudhwa National Park in Uttar Pradesh has a population of only 38 individuals.

By 2014, the population in Assam had increased to 2,544 Indian rhinos, marking a 27% rise since 2006, despite the loss of more than 150 individuals to poaching during this period. In Kaziranga National Park, the population was estimated at 2,048 individuals in 2009. By the same year, the population in Pobitora Wildlife Sanctuary had increased to 84 individuals within an area of 38.80 km2.

Ecology of Indian Rhinoceros
Indian rhinoceroses primarily graze on grasses but their diet also includes leaves, twigs, and branches of shrubs and trees such as Lagerstroemia indica, as well as flowers, fruits like Ficus religiosa, and submerged and floating aquatic plants.

These rhinos exhibit various social groupings. Bulls are typically solitary, except during mating and fighting. Cows are mostly solitary when without calves, but mothers remain close to their calves for up to four years after birth, sometimes allowing older calves to accompany them even after a new calf is born. Subadult bulls and cows also form consistent groups. Groups of young bulls, usually two or three, often form on the periphery of dominant bulls` territories, presumably for added protection. Young cows are slightly less social. Short-term groupings, especially at forest wallows during the monsoon season and in grasslands during March and April, are also common. These groups can consist of up to 10 rhinos, typically a dominant male with females and calves.

Indian rhinos produce a range of vocalizations, including snorting, honking, bleating, roaring, squeak-panting, moo-grunting, shrieking, groaning, rumbling, and humphing. They also use olfactory communication. Regular bathing is part of their behavior, with their skin folds trapping water even after exiting wallows. They are proficient swimmers and can run at speeds of up to 55 km/h for short periods. Despite their excellent hearing and sense of smell, their eyesight is relatively poor.

Males have home ranges of approximately 2 to 8 km2, overlapping with each other. Dominant males tolerate the passage of other males through their territories except during mating season, when conflicts may arise. Indian rhinos face few natural predators, with tigers posing the most significant threat, particularly to unguarded calves. However, adults are less vulnerable due to their size.

Diseases spread by parasites like leeches, ticks, and nematodes, including Bivitellobilharzia nairi, pose risks to Indian rhinos. Anthrax and sepsis are also known to occur among their populations.

Threats to Indian Rhinoceros
The Indian Rhinoceros is classified as Vulnerable on the IUCN Red List due to habitat fragmentation and restriction to less than 20,000 km2 of area. According to estimates from August 2018, the global population stood at approximately 3,588 individuals. Historically, these rhinos roamed across the entire Indo-Gangetic Plain. However, extensive hunting and agricultural expansion drastically reduced their range to just 11 sites in northern India and southern Nepal. By the early 1990s, their population dwindled to an estimated 1,870 to 1,895 individuals. Conservation efforts initiated by the government have since led to a population increase, though poaching remains a persistent threat.

Sport hunting emerged as a prevalent activity during the late 19th and early 20th centuries, significantly contributing to the decline of Indian Rhinoceros populations. These rhinos were relentlessly targeted and hunted down. Poaching for their horns emerged as the primary factor driving the decline of Indian Rhinoceros populations, even after conservation efforts were initiated at the beginning of the 20th century, leading to the cessation of legal hunting.

Conservation of Indian Rhinoceros
The Indian rhinoceros is classified as vulnerable by the IUCN Red List as of 2018 and has been globally listed in CITES Appendix I since 1975. Both the Indian and Nepalese governments have made significant efforts toward the conservation of Indian Rhinoceros populations, particularly with assistance from organizations such as the World Wide Fund for Nature (WWF) and other non-governmental organizations. In 1910, all rhino hunting in India was prohibited, marking a crucial step in rhinoceros conservation efforts.