The nilgai (Boselaphus tragocamelus), sometimes called nilgau, is an antelope, and is one of the most commonly seen wild animals of central and northern India and eastern Pakistan; it is also present in parts of southern Nepal. The species has become extinct in Bangladesh. The mature males appear ox-like and are also known as blue bulls. The nilgai is the biggest Asian antelope.
A blue bull is called a nil gai or nilgai in India, from nil meaning blue and gai meaning a bovine animal (literally 'cow'). In fact nilgai were known as the Nilghor (nil = blue, ghor = horse) during the rule of Aurangzeb (Mughal Era).
Nilgai stand at the shoulder and measure in head-body length, with a tail. Males are larger than females, weighing around , compared with the adult female weight of around .
Nilgai have thin legs and a robust body that slopes down from the shoulder. They show marked sexual dimorphism, with only the males having horns. Adult males have a grey to bluish-grey coat, with white spots on the cheeks and white colouring on the edges of the lips. They also have a white throat bib and a narrow white stripe along the underside of the body that widens at the rear. The tips of the long tufted tail and of the ears are black. They also possess a tubular shaped "pennant" of long, coarse, hair on the midsection of the throat.
The males have two black conical horns, arising close together just behind the eyes. The horns are project upwards, but are slightly curved forward; they measure between in a fully grown adult. Although the horns are usually smooth, in some older males they may develop ring-shaped ridges near the base.
In contrast, females and young are tawny brown in colour, although otherwise with similar markings to the male; they have no horns and only a very small "pennant". Both sexes have an erectile mane on the back of the neck, terminating in a bristly "hog-tuft" just above the shoulders.
Nilgai antelopes are found throughout most of India, from the base of the Himalayas in the north, down to the state of Karnataka in the South, being absent only in eastern Bengal, Assam, the Malabar Coast, and regions close to the Bay of Bengal. They are found in small numbers along the Indian borders with Pakistan and Nepal.
They inhabit the Gir forest and from all along the entire eastern length of Pakistan and over across the border of Rajasthan in the West to the states of Assam and West Bengal in the East. In Nepal, they occur patchily in the southern lowlands.
Historic notes mention the nilgai in southern parts of India but there have also been suggestions that they may be a feral population:
The population density of nilgai in central India is .
Nilgai pursued by dholes
, as drawn by Robert Armitage Sterndale in Denizens of the Jungles
Nilgai have existed north of Bangalore and probably still do.
Nilgai were introduced in the US state of Texas in the 1920s by the King Ranch for recreational purposes. Over the years some escaped and they are now free ranging in various southern portions of the state.
Habitat and diet
Nilgai are habitat generalists, living in grasslands and woodlands where they eat grasses, leaves, buds, and fruit. They avoid dense forest and prefer the plains and low hills with shrubs, but may also be found in cultivated areas.
Blue bulls are usually found in their favoured areas of scrub jungle (acacia forests) grazing upon succulent kader grass. They are not averse to crossing marshlands.
Nilgai (blue bull): Leaf from the Shah Jahan Album, Mughal, Jahangir period (1605 27), ca. 1620
Nilgai are diurnal, and tend to form single sex herds outside of the breeding season. Herds are not of fixed composition, with individuals joining and re-joining through the year. Female herds typically contain three to six adults, together with their calves, whereas bulls form herds of anything from two to eighteen individuals. In winter, male blue bulls form herds of 30 to 100 animals in northern India.
Nilgai herds in Texas have been reported to have an average home range of . Both males and females mark their territory by defecating in fixed locations on open ground, with piles building up to reach at least in diameter. They also possess scent glands on the legs and close to the feet, which they may use to scent mark their daily resting places. They are generally quiet animals, but have been reported to make short guttural grunts when alarmed, and for females to make clicking noises when nursing young.
Nilgai can be seen with black buck in the open plains, and in the lower Terai regions they may be seen together with chital and hog deer. The chital and hog deer, being comparatively smaller in size, usually keep a respectful distance from the much larger nilgai. Sambar frequent hills and dense forests and are rarely found in the same habitat as nilgai.
Predators of nilgai include tigers and leopards, although the latter are only capable of capturing calves, and not fully grown adults. scat analysis has shown that lions, although present in some parts of the nilgai's range, generally do not prey on the animals, with nilgai comprising less than 3% of their diet. Other predators include wolves and striped hyenas.
A blue bull can survive for days without water, but they live close to waterholes. The deserts earlier limited their range, but the extension of irrigation canals and proliferation of tube-wells in the Thar desert have helped them colonise the desert districts of Jodhpur, Barmer, Jaisalmer, Bikaner and Ganganagar.
Nilgai female and calves
Male fighting Breeding occurs in late autumn to early winter. Prior to the rut, males compete to establish dominance. Males display to each other by holding their head erect and presenting the white patch and tassel on their throats. They may also rush towards one another, holding their heads down so that their horns project forwards. Such displays often escalate to direct conflict, including head-butting and neck-fighting. Although bulls have thick skin on their heads and necks, which helps protect them in such fights, serious injury can nonetheless occur. Females also compete to establish dominance around the time of the rut, including neck-fighting, and butting rivals on their shoulders or flanks.
Males mate with several females over the course of the breeding season, but do not establish clear harems, instead wandering between different all-female groups. Courtship lasts about 45 minutes, with the male adopting a stiff gait with tail held erect, and the female responding with a flehmen gesture and raised tail before permitting mounting.
Gestation lasts 243 to 247 days, resulting in the birth of twins in about 50% of cases, although births of one or three do occur. Females become solitary towards the end of their pregnancy, and hide their young from other nilgai for the first month of their life. The calves are precocious, being able to stand within forty minutes of birth, and they begin to forage during their fourth week of life. Calves usually weigh at birth.
Females reach sexual maturity at around two years of age, and males by their third year, although the most reproductively active bulls are typically at least four or five years old. They live for around twelve or thirteen years in the wild, but have survived for up to 21 years in captivity.
Tamed nilgai, male, Lakeshwari, Gwalior district The estimated population of nilgai in India is approximately 100,000. Wild populations also exist in the US states of Alabama and Texas and the Mexican state of Tamaulipas where they have escaped from private exotic ranches. The population around the Texas-Mexico border is estimated to be around 30,000 and the King Ranch where Nilgai were first released now has around 10,000 of them.
Like many Indian animals, nilgai are often victim to vehicular accidents, and their carcasses are often seen on major highways in northern India. The main threat to this species is the loss of habitat due to human population growth. However, nilgai are a crop menace, causing large-scale damages especially along the Gangetic belt, especially in the Rohilkhand division of Uttar Pradesh. It has been declared as vermin in northern India, and they may be legally hunted after obtaining a permit. Nevertheless the local belief, that nilgai are a cow and hence sacred, has protected it against hunting.
Some Texas "exotic ranches" offer nilgai hunting. Nilgai meat is said to resemble beef, but with lower fat content and less flavour; one study showed that tasting panels preferred wieners made from 30% nilgai meat mixed with beef to those with higher nilgai meat content.
Distinctive white marks are clearly seen on the feet of this male nilgai
- Menon, Vivek. A Field Guide to Indian Mammals. Dorling Kindersley, Delhi, 2003.
- Sheffield, William J., et al. The Nilgai Antelope in Texas (College Station: Texas Agricultural Experiment Station, Texas A&M University System, 1983).
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