Nilgai antelope (Boselaphus tragocamelus Pallas) were apparently brought to the United States from India as zoo animals before the mid-1920s and were released in South Texas about 1930. The Hindi word nilgaw ("blue bull") refers to the bluish color of the adult male, and blue bull is another name for the animal. Nilgai probably evolved in open, dry Indian forests during the Tertiary geological period. They are classified as bovids (family Bovidae), and with their closest relative, the four-horned antelope (Tetracerus quadricornis), are the only living representatives of the tribe Boselaphini. Nilgai are the largest of the Indian antelopes. Adult bulls weigh 200–240 kilograms, occasionally more. Cows weigh 150–200 kilograms and calves about seven kilograms at birth. The generally blue-gray adult bulls have black legs, and some may be brown-tinged, particularly younger bulls. Cows and calves are pale brown. All have similar dark and white markings on their ears and legs. Only the males have horns, which are black-colored, short (about eighteen centimeters), sharp, and bicurved. The hair of adults is thin in density, wiry, and somewhat oily. Their skin is thick, particularly on the chest and neck of the bulls, where it forms a dermal shield. The eyesight and hearing of nilgai are considered equal to or better than that of white-tailed deer, but their sense of smell less acute. They have speed and endurance and, over rough terrain, may outrun a horse with rider. Nilgai make several low-volume vocalizations, including a short, guttural "bwooah" when alerted. Calves may bawl and may make a grunting sound while nursing. In India nilgai occur from the foothills of the Himalayan Mountains southward to Mysore. They live on a variety of land types from hillsides to level ground with scattered grass steppes, trees, and cultivated areas, but not in thick forests. Their habitats are characterized by paths, waterholes, defecation sites, and resting cover. Nilgai were common in India and parts of Pakistan during the 1880s and were hunted for sport by the British. Besides man, the tiger is their principal Asian predator. In the mid-1980s both nilgai and tigers had drastically declined because of overshooting and loss of habitat to development.
The King Ranch pioneered the release of nilgai in Texas. Between about 1930 and 1941 the ranch made several acquisitions of nilgai zoo stock and released them in Kenedy County. With limited hunting and predation, protection, and favorable habitat, nilgai adapted well. Their primary range now includes the area from Baffin Bay south to near Harlingen. They have been distributed to numerous counties by landowners releasing brood stock. Approximately 15,000 nilgai are now on Texas rangelands. They will probably not become widespread. They suffer in extreme cold, and even in temperate South Texas they may die during unusually cold winters when food is scarce.
Nilgai segregate into male and female groups except during the breeding season. Bulls do not maintain a fixed territory but defend a space around themselves. Fighting occurs between dominant bulls, and serious injury or death sometimes results. Nilgai make dung piles by defecating repeatedly on the same sites. The social and territorial significance of this habit is not known. Some breeding takes place year-round, but the principal breeding period in Texas is November through March. At that time breeding groups of one dominant bull and one to several cows are found. The peak calving period is September through November. Female nilgai breed at age two to three years, whereas males may not breed until their fourth year. The gestation period is approximately 245 days. Twinning is common, and triplets occur occasionally. The cow-to-calf ratio of Texas nilgai is approximately seventy-five to 100, and the sex ratio at birth is approximately even.
In Asia nilgai eat mainly woody plants supplemented by agricultural crops. Grass forms the bulk of their diet in Texas. They upgrade their diet nutritionally by eating forbs, browse, and plant parts (flowers, seeds, fruit, leaves, stem tips). In the absence of preferred food they readily alter their diet. Nilgai in Texas harbor low numbers of parasites. Gastrointestinal nematodes and ticks, including fever ticks, have been taken from them. In India they share certain diseases with livestock and wildlife. Perhaps the most universal of these are foot-and-mouth disease and malignant catarrhal fever. Although these diseases occur in Texas livestock, they have not been found in Texas nilgai. The species has not been intensively studied. Baseline studies of distribution, social organization, behavior, food habits, and population ecology have been published by Texas A&M University, but more ecological, economic, and management information is needed. The limited hunting of nilgai in Texas and their high rate of increase make the control of their numbers a major management concern. Developing economic uses may be the best means of controlling the nilgai and assuring their compatibility on Texas ranges. Currently, sport hunting and meat supply are the best potential uses for these antelope.