|Male four-horned antelope|
|Female four-horned antelope|
The four-horned antelope (Tetracerus quadricornis), or chousingha, is a species of small antelope found in open forest in India and Nepal. It is the only species currently classified in the genus Tetracerus. Standing only 55 to 64 cm (22 to 25 in) at the shoulder, it is the smallest of Asian bovids. Males of the species are unique among extant mammals in that they possess four permanent horns. The species is listed as Vulnerable by the IUCN due to habitat loss.
The four-horned antelope is among the smallest Asian bovids, standing just 55 to 64 cm (22 to 25 in) tall at the shoulder, and weighing 17 to 22 kg (37 to 49 lb). It has a generally slender build, with thin legs and a short tail. The coat is yellow-brown or reddish, fading to a whitish colour on the underparts and the insides of the legs. A black stripe of hair runs down the anterior surface of each leg, with black patches on the muzzle and the backs of the ears. Females have four teats, located far back on the abdomen.
The most distinctive feature of the animal is the presence of four horns; a feature unique among extant mammals. Only the males grow horns, usually with two between the ears and a second pair further forward on the forehead. The first pair of horns appear at just a few months of age, and the second pair generally grow after 10 to 14 months. The horns are never shed, although they may be damaged during fights. Not all adult males have horns; in some individuals, especially those belonging to the subspecies T. q. subquadricornis, the forward pair of horns is absent or represented only by small, hairless bumps. The hind pair of horns reaches 7 to 10 cm (2.8 to 3.9 in) in length, while the forward pair is usually smaller, at just 2 to 5 cm (0.79 to 2.0 in).
Most wild four-horned antelope are found in India, with small, isolated populations in Nepal. Their range extends south of the Gangetic plains down to the state of Tamil Nadu, and east as far as Odisha. They also occur in the Gir Forest National Park of western India.
Four-horned antelope live in a variety of habitats across their range, but prefer open, dry, deciduous forests in hilly terrain. They tend to remain in areas with significant vegetation cover from tall grasses or heavy undergrowth, and close to a supply of water. They generally stay away from human-inhabited areas. Predators of four-horned antelopes include tigers, leopards, and dholes.
Three subspecies of four-horned antelope, Tetraceros quadricornis quadricornis, are recognized: 
Four-horned antelope are generally solitary animals, although they are occasionally found in groups of up to four individuals. They are sedentary, rather than nomadic, and may defend exclusive territories. Males tend to become very aggressive towards other males during mating seasons. Adults make alarm calls that sound like a husky 'phronk', and other, quieter calls to communicate with young or other adults. They also communicate through scent marking, leaving piles of droppings in their territories, and marking vegetation using large scent glands in front of the eyes.
They are herbivorous, feeding on soft leaves, fruits, and flowers. Although the precise details of their diets in the wild are unknown, they have been observed to prefer plants such as Indian plum, Indian gooseberry, Bauhinia, and Acacia in artificial trials.
The breeding season lasts from May to July, and males and females generally remain apart for the remainder of the year. Courtship behaviour consists of the male and female kneeling and pushing at each other with intertwined necks, followed by ritual strutting by the male. Gestation lasts about eight months, and results in the birth of one or two young. At birth, the young are 42 to 46 cm (17 to 18 in) long, and weigh 0.74 to 1.1 kg (1.6 to 2.4 lb). Young remain with the mother for about a year, and reach sexual maturity at around two years.
The four-horned antelope is currently regarded as the only species in the genus Tetracerus. Both genetic and morphological studies, however, confirm it as one of only two living members of the tribe Boselaphini, with its closest living relative being the nilgai. This group originated at least 8.9 million years ago, in much the same area where the four-horned antelope lives today, and may represent the most "primitive" of all living bovids, having changed the least since the origins of the family.
Living in a densely populated part of the world, the four-horned antelope is threatened by loss of its natural habitat to agricultural land. In addition, the unusual four-horned skull has been a popular target for trophy hunters. Only around 10,000 four-horned antelope are estimated to remain alive in the wild, although many are in protected animal conservation areas. The species is protected under the Indian Wildlife Protection Act and the Nepalese population is listed in Appendix III of CITES. The four-horned antelope is considered Vulnerable by the IUCN, primarily due to increasing habitat loss.
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