The nilgai is the largest Asian antelope and is native to the Indian subcontinent. This sturdy thin-legged antelope is characterized by a sloping back, a deep neck with a white patch on the throat, a short mane of hair behind and along the back ending behind the shoulder, and around two white spots each on its face, ears, cheeks, lips, and chin. A column of coarse hair, known as the "pendant" can be observed along the dewlap ridge below the white throat patch. The tufted tail has a few white spots and is tipped with black. The forelegs are generally longer, and the legs are often marked with white "socks". While females and juveniles are orange to tawny, males are much darker - their coat is typically bluish-grey. A white stripe extends from the underbelly and broadens as it approaches the rump, forming a patch lined with dark hair. Males have thicker skin on their head and neck that protect them in fights. Only males possess horns, though a few females may be horned as well.
Nilgai occur in India, Nepal, and Pakistan. Significant numbers occur in the Terai lowlands in the foothills of the Himalayas. These antelopes are abundant across northern India. Nilgai prefer areas with short bushes and scattered trees in scrub forests and grassy plains. They are common in agricultural lands but hardly occur in dense woods. They can adapt to a variety of habitats. Though sedentary and less dependent on water, nilgai may desert their territories if all water sources in and around it dry up.
Nilgai are active mainly during the day. They are social animals and live in groups. These groups are generally small, with 10 or fewer individuals, though groups of 20 to 70 individuals can occur at times. Females and juveniles do not interact with males, except during the mating season. Nilgai mark their territories by forming dung piles as much as 50 centimeters (20 in) in radius. They have good hearing and eyesight but they do not have a good sense of smell. They are typically tame creatures but may appear timid and cautious if harassed or alarmed; instead of seeking cover they would flee up to 300-700 meters (980-2,300 ft) on galloping-away from the danger. Nilgai are generally quiet but will make short guttural grunts when alarmed, and females make clicking noises when nursing young. Alarmed individuals, mainly calves, give out a coughing roar that lasts half a second but can be heard by herds less than 500 meters (1,600 ft) away and responded to similarly. Fights take place in both sexes and involve pushing their necks against each other or ramming into one another using horns. Fights can be gory; despite the protective skin deep, lacerated wounds and even deaths might occur. Display behavior focuses on the throat patch and the beard and threatening opponents by pointing the horns toward them.
Nilgai mate throughout the year, with a peak in December-March. The time of the year when these peaks occur varies geographically. During this time rutting males move about in search of females. Males become aggressive and fight among themselves for dominance. These fights are characterized by displays of the enlarged chest, the throat patch and the beard while holding the head upright; and threatening the opponent by running with the horns pointed toward him and circling him. The victorious bull would protect the vicinity of the targeted female from other males. Females give birth to a single calf or twins after the gestation period that lasts 8 to 9 months. Calves are born precocial; they are able to stand within 40 minutes of birth and forage by the fourth week. Pregnant females isolate themselves before giving birth and newly born calves are kept in hiding for the first few weeks of their lives. Weaning occurs at 10 months of age and at this time young males leave their mothers to join bachelor groups. Females become reproductively mature at 3 years of age while males are ready to breed when they are 4-5 years old.
The main threats to nilgai include hunting, deforestation and habitat degradation. These antelopes are also considered an agricultural pest in several north Indian states. The populations of nilgai in India are so large that farmers have pleaded to the government to cull them. Nilgai herds raid and trample crop fields, often causing considerable damage and food shortages so farmers use live electric wires to guard their farms, which kills other animals as well.
According to IUCN, the nilgai is abundant and widespread throughout its range but no overall population estimate is available. However, there are estimates of its populations in specific areas: India - over 100,000 individuals; Texas, USA: Texas ranches - 37,000 feral nilgai; around Texas-Mexico border - 30,000 individuals. Currently, nilgai are classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.