Boselaphus tragocamelus (Pallas, 1766)

Don E. Wilson & Russell A. Mittermeier, 2011, Bovidae, Handbook of the Mammals of the World – Volume 2 Hoofed Mammals, Barcelona: Lynx Edicions, pp. 444-779 : 591-592

15.

Nilgai

Boselaphus tragocamelus

French: Nilgaut / German: Nilgau / Spanish: Nilgo

Other common names: Blue Bull, Bluebuck, White-footed Antelope

Taxonomy. Antilope tragocamelus Pallas, 1766 ,

Bengal, India.

Pallas’s description was based on earlier accounts of the “tragelaphus” and on the description of a male Nilgai in London (the lectotype), which had been brought to Bengal from a very remote part of the “Mogul’s Dominions.” Monotypic.

Distribution. NE Pakistan, lowland areas of S Nepal, and Peninsular India. Introduced into Italy near Rome (extirpated during World War II), South Africa, S USA (Texas), and N Mexico (Coahuila, Nuevo Leon, Sonora, Tamaulipas & Veracruz).

Descriptive notes. Head-body 180-210 cm (males) and 170 cm (females), tail 46-53 cm (males) and 45 cm (females), shoulder height 120-140 cm; weight 200-288 kg (males) and 120-212 kg (females). The Nilgai is a large bovid, somewhat equine in appearance, with a deep and compressed neck, a tufted tail reachling the hocks, hindlimbs that are shorter than the front legs, and high withers. Males and females vary greatly in coloration, and mass. Only males have horns, which characteristically arise close together just behind the orbits and are directed upward. They are short (15-24 cm at maturity), black, generally smooth, sharp, and nearly straight, with no catching arch. Horns are subconical above and triangular at the base (circumference about 20 cm) with a flat posterior side and a ridge in the front; they may develop one or more base rings annually after 3—4 years of age. Horn characteristics of adult males are core surface, 70-8 cm?; sheath surface, 100-7 cm?; and sheath thickness, 0-38 cm. The adult male pelage is dark gray, but can vary from bluish to brownish-gray. The mane, terminal half of the outside of the ear, two spots inside the ear, and the tip of the tail are black. A patch on the throat (gular patch), two spots on each cheek, and the lips, chin, inside of the ears (except for the two black spots), lower surface of the tail, the abdomen, and two rings above and below the fetlock are white. Females, calves, and young males are tawny brown with the same white markings as males. Males have a pronounced beard of coarse hair directly beneath the white gular patch; it is rudimentary in females. Both sexes have a short, bristly mane that extends the length of the neck and terminates in a tuft at the nape of the neck. The mane and terminal tuft are darker and more prominent in adult males than in females and other age classes. Preorbital glands are small, with no lachrymal fossa. Interdigital and unguicular glands are present, but there are no inguinal glands. Frontals and parietals of the skull are almost in a single plane, forming a right angle with the occipital. Dental formulais 10/3, C0/1,P 3/3, M 3/3 (x2) = 32. The molars are very hypsodont, with tall crowns and a large accessory column on upper molars. Nilgai can be aged by the eruption pattern and wear of their teeth: 1-2 year olds, M* within alveoli, M*just erupted, and milk dentition weakly to moderately worn; three year olds, premolars unworn,last milk tooth worn, and M?just erupted; 4-5 year olds, full permanent dentition in first stages of wear; and more than six years old, full permanent dentition in advanced stages of wear.

Habitat. In its native range, mainly in India and Nepal, the Nilgai is a habitat generalist, preferring level to undulating terrain with scattered short trees and brush interspersed with open grassy plains. They rarely occur in dense forest. Nilgai can be pests in agricultural areas, depredating fields at night and returning to cover during the day. Densities in India are 0-2-11-4 ind/km?®, depending on habitat conditions, predation, degree of protection, and competition with livestock. Where exotic in southern Texas, USA, Nilgai avoid dense woodlands and frequent improved pastures, sparse forests of live oak (Quercus virginianus) and scrub, and coastal prairies. Densities in southern Texas are 3-1-4-8/km®. On both continents, availability of free water limits Nilgai distribution. All sexes and age classes visit water sources regularly and are not averse to entering water to drink. In captivity neonates begin to drink at three weeks of age. Nilgai also have been translocated to Mexico, South Africa, and Italy (now extirpated) and occur in various states of confinement or have escaped and are free-ranging.

Food and Feeding. Nilgai are herbivorous and seasonally semi-frugivorous. Their premaxillary shape suggests a mixed feeder. Dietary selection varies seasonally and includes grasses (Cenchrus, Cynodon dactylon, Desmostachya bipinnata, Scirpus tuberosus, Vetioeria zizanoides), woody vegetation (Acacia nilotica, A. senegal, A. leucophloea, Clerodendrum phlomidis, Crotalaria burhia, Indigofera oblongifolia, Morus alba, Zizyphus nummularia), and herbaceous species (Cocculus hirsutus, Euphorbia hirta, Sida rhombifolia). Woody vegetation dominates Nilgai diets in dry tropical forests of India. Frugivory occurs seasonally; in Keoladeo National Park, India, seeds of 34 plant species germinated from Nilgai feces. Seeds of Paspalum distichum occurred in feces year-round, seeds of Acacia nilotica and Prosopis juliflora (both with fleshy fruits, but the latter an invasive exotic species in India) occurred in feces during the hot-dry season, and seeds of Enchinochloa crus-galli occurred in feces during the monsoon. In Texas, Nilgai consume at least 167 species of plants: 66 grasses, 89 herbaceous species, and twelve woody plants. The average annual diet in Texas is 66% grass, 25% herbaceous species, and 15% browse. Generally, adult males eat more grass throughout the year than adult females, and subadults eat more herbaceous vegetation than adults of either sex. Seeds, mainly from mesquite (Prosopis glandulosa), are seasonally important to Nilgai in Texas. In Ranthambhore National Park, India, Nilgai and Deccan Chinkara ( Gazella bennettii) form a bovid guild and select Acacia—Butea habitats during summer and winter, in contrast to sympatric Chital (Axis axis) and Sambar (Rusa unicolor), which prefer Anogeissus—Grewia forests. In contrast to the cervids, Nilgai tolerate livestock grazing and associated degradation of grass cover.

Breeding. The breeding and birthing seasons of Nilgai are extended: generally October-February and June-Octoberin India and August-December and April-August in Texas (where neonates can be observed throughout the year). Female sexual maturity typically occurs at two years of age, with the first parturition after three years. Gestation is 243-247 days. Twinning is common; 50% ofbirths are twins in southern Texas, and triplets are occasionally noted. Females can breed shortly after parturition. Interparturition intervals for three captive females were 319-664 days (sample eight litters) and averaged 436 days; one captive female produced seven litters in seven years and eight months. Generally, males 4-5 years old are the most active breeders, but testes are histologically active by three years of age. As rut approaches, adult males interact aggressively, and vigorous fights establish dominance among them. Solitary breeding males try to maintain an area of dominance around them as they move among different groups of females, which generally results in mutual avoidance among breeding males. Dominance interactions between breeding males include lateral displays with various head and neck displays that maximize appearance of the chest, white gular patch, and beard (arched-necked display, straight-necked display) and frontal head-erect displays (similar to alert posture), often at distances of greater than 75 m between conspecifics. Threats are more serious than dominance displays and include a straight-necked threat displayed frontally and usually within 10 m of a conspecific (while stationary, walking, or running toward opponent) and a rush threat from a normal stance or after a lateral display with lowered neck, head toward the ground, and horns horizontal. During such interactions, contact and goring of the thighs or flank are common, and chases of up to 750 m have been observed. While displaying, males may circle one another crouched and with a stiff posture. Two types of fights occur between males: head butting with horns, and neck fighting, either in standing or kneeling position. The thick dermal shield on the neck and chest of the male Nilgai is protective, but fighting of either type can result in serious goring and mortality; puncture wounds and even protruding viscera have been observed. Females also neck fight and display intrasexual agonistic behavior by rushing, head butting other females on their shoulders, flanks, or sides, and threatening with flattened ears and stretched neck. During breeding, generally only one mature male accompanies a female group at a time, sometimes for only a few hours. Even during the breeding season, female groups usually do not have a breeding male present. Males do not attempt to form or defend harems in a spatially defined breeding territory. Courtship is simple and may last only 45 minutes; a breeding male will approach a female stiffly, body stretched lengthwise and tail erect, with the tuft at a right-angle kink; the female typically holds her head close to the ground and meanders forward; the male then licks and nuzzles the female’s perineum. If she is receptive, the female will raise her tail and elicit a flehmen (lip curl) response from the male, who then rests his chin on her rump, pushes his chest forward to touch her, and mounts. Copulation is terminated by the female; no post-copulation display has been noted. Pregnant females become solitary as parturition approaches and keep neonates hidden from other conspecifics for about one month. Neonates nurse from a reverse parallel position, and average nursing bouts can last as long as seven minutes; offspring show interest in forage during their fourth week. Maximum life span is 12-13 years in the wild and 20-21 years in captivity.

Activity patterns. Mainly crepuscular, but can be active throughout the day and night. Where Nilgai use agricultural fields, they can be largely nocturnal. Nilgai can be very wary, likely related to human harassment, but early accounts from Hindu-dominated areas in India, where they were not hunted or harassed, described them as very tame. Handreared individuals have been used in feeding and nutritional evaluations. In southern Texas, males and females are equally likely to flee approaching vehicles; mean flight distance was about 300 m, but a galloping flight response (up to 48 km /h) was noted even up to 700 m. Individuals did not seek cover but ran away from the disturbance.

Movements, Home range and Social organization. Nilgai are non-migratory, but individuals are capable of moving considerable distances if ambient conditions such as drought or restricted food availability dictate. No home range information exists for Nilgai in their native range, but in Texas, home ranges in a 5680ha fenced area averaged 4-3 km?® (0-6-8-1 km?). Males were transient, often traversing their entire home range daily. Nilgai are not as gregarious as other herding ungulates and occur in relative small groups throughout the year. Adult males segregate from females and subadults during non-breeding. Annual group sizes in India are 1-9-2-9 individuals; observations of male prevalence in groups during breeding in Nepal found one male in 37% of the groups, two males in 28%, three males in 20%, and more than four males in 15%. Outside of the breeding season in India, herd composition changes constantly, and includes small groups of 1-2 adult females and their offspring; mixed herds of 3-6 adult females, yearling females, and an occasional calf; and male groups of 2-18 individuals. Play behavior among young Nilgai is apparent but not frequent. Play activities in Nilgai as young as three months old include bounding with a spring start and landing stiff-legged, chasing, and play-fighting (rudimentary neck fighting) with erecttails. Communication and social interactions among groups and individuals are maintained with various guttural and low-pitched vocalizations and by repeated defecation in conspicuous fecal piles (suggesting a form of advertisement) that are often more than 3 m and up to 6 m in diameter. In southern Texas,fresh feces are added to a pile, on average, every 3-7 days. Defecation postures of Nilgai are characteristic and exaggerated; males stand with their rear legs spread 0-6-1 m, rump lowered,tail erect at least above horizontal and often near vertical, and head and neck erect and forward. This position is often maintained for more than ten seconds after defecation. Forward spraying of urine by males often accompanies defecation. Females defecate in a similar manner, but their posture is less exaggerated than in males and, unlike males, females will defecate while walking.

Status and Conservation. Classified as Least Concern on The IUCN Red List. There are about 100,000 Nilgai in India, very few in Pakistan, and they were extirpated from Bangladesh; introduced population in southern Texas numbers about 37,000. Various references to “cow” and “bull” in its common name have led to local Hindu beliefs that the Nilgai is sacred and should be protected from hunting. Although generally protected from hunting in India, such protection is often waived to minimize depredation complaints. As an exotic in Texas, unlimited numbers of Nilgai can be harvested throughout the year by hunters with a valid hunting license.

Bibliography. Ables & Ramsey (1972), Acharjyo & Misra (1975b), Alvarez-Romero & Medellin (2005), Bagchi, Goyal & Sankar (2003a, 2003b, 2004), Berwick (1974), Blanford (1888), Bohra et al. (1992), Dinerstein (1979, 1980), Fall (1972), Goldman & Stevens (1980), Gosling (1985), Huffman (2006a), Jones (1982), Kostopoulos (2005), Leslie (2008), Lever (1985), Lochmiller & Sheffield (1989), Long (2003), Lundrigan (1996), Lydekker & Blaine (1914), Mallon (2008a), Middleton & Mason (1992), Mungall & Sheffield (1994), Picard et al. (1996), Pocock (1910), Prater (1980), Rahmani (2001), Sankar et al. (2004), Schaller (1967), Sclater & Thomas (1900), Sharma (1981), Sheffield (1983), Sheffield, Ables & Ball (1971), Sheffield, Fall & Brown (1983), Shrestha (2001), Solounias & Moelleken (1993).

Figures

14. Saola (Pseudoryx nghetinhensis), 16. Chowsingha (Tetracerus quadricornis), 17. Nyala (Nyala angasii)

Distribution. NE Pakistan , lowland areas of S Nepal , and Peninsular India . Introduced into Italy near Rome (extirpated during World War II), South Africa , S USA (Texas), and N Mexico (Coahuila, Nuevo Leon, Sonora, Tamaulipas & Veracruz).