Ecology and behaviour
Where gaur have not been disturbed, they are basically diurnal. In other areas, they have become largely nocturnal due to forest molestation caused by people. In central India, they are most active at night, and are rarely seen in the open after 8 o'clock in the morning. During the dry season, herds congregate and remain in small areas, dispersing into the hills with the arrival of the monsoon. While gaur depend on water for drinking, they do not seem to bathe or wallow.
In January and February, gaur live in small herds of eight to 11 individuals, one of which is a bull. In April or May, more bulls may join the herd for mating, and individual bulls may move from herd to herd, each mating with many cows. In May or June, they leave the herd and may form herds of bulls only or live alone. Herds wander 2–5 km (1.2–3.1 mi) each day. Each herd has a nonexclusive home range, and sometimes herds may join in groups of 50 or more. The average population density is about 0.6 animals per square kilometre (1.5 animals per square mile), with herds having home ranges of around 80 km2 (31 sq mi).
Gaur herds are led by an old adult female, the matriarch. Adult males may be solitary. During the peak of the breeding season, unattached males wander widely in search of receptive females. No serious fighting between males has been recorded, with size being the major factor in determining dominance. Males make a mating call of clear, resonant tones which may carry for more than 1.6 km (0.99 mi). Gaur have also been known to make a whistling snort as an alarm call, and a low, cow-like moo.
In some regions in India where human disturbance is minor, the gaur is very timid and shy despite their great size and power. When alarmed, gaur crash into the jungle at a surprising speed. However, in Southeast Asia and South India, where they are used to the presence of humans, gaur are said by locals to be very bold and aggressive. They are frequently known to go into fields and graze alongside domestic cattle, sometimes killing them in fights. Gaur bulls may charge unprovoked, especially during summer, when the intense heat and parasitic insects make them more short-tempered than usual. To warn other members of its herd of approaching danger, the gaur lets out a high whistle for help.
Feeding ecology
Wild gaur graze and browse on a wider variety of plants than any other ungulate species of India, with a preference for the upper portions of plants, such as leaf blades, stems, seeds and flowers of grass species, including kadam.
During a survey in the Bhagwan Mahaveer Sanctuary and Mollem National Park, 32 species of plants were identified as food for gaur. They consume herbs, young shoots, flowers, fruits ofelephant apple (Dillenia ssp.) with a high preference for leaves. Food preference varies by season. In winter and monsoon, they feed on preferably fine and fresh grasses and herb species of the legume family, such as tick clover (Desmodium triflorum), but also browse on leaves of shrub species such as karvy (Strobilanthes callosus), Indian boxwood (Gardenia latifolia),mallow-leaved crossberry (Grewia abutifolia), East-Indian screw tree (Helicteres ssp.) and the chaste tree (Vitex negundo). In summer, they also feed on bark of teak (Tectona grandis), on fruit of golden shower tree (Cassia fistula), and on the bark and fruit of cashew (Anacardium occidentale). Gaur spent most of their daily time feeding. Peak feeding activity was observed between 6:30 and 8:30 am and between 5:30 and 6:45 pm. During the hottest hours of the day, 1:30 to 3:30 pm, they rest in the shade of big trees.
They may debark trees due to shortages of preferred food, and of minerals and trace elements needed for their nutrition, or for maintaining an optimum fiber/protein ratio for proper digestion of food and better assimilation of nutrients. They may turn to available browse species and fibrous teak bark in summer as green grass and herbaceous resources dry up. High concentrations of calcium (22400 ppm) and phosphorus (400 ppm) have been reported in teak bark, so consumption of teak bark may help animals to satisfy both mineral and other food needs. Long-term survival and conservation of these herbivores depend on the availability of preferred plant species for food. Hence, protection of the historically preferred habitats used by gaur is a significant factor in conservation biology.
Reproduction
Gaur have one calf (or occasionally two) after a gestation period of about 275 days, about nine months, a few days less than domestic cattle. Calves are typically weaned after seven to 12 months. Sexual maturity occurs in the gaur's second or third year. Breeding takes place year-round, but typically peaks between December and June. The lifespan of a gaur in captivity is up to 30 years.
Natural enemies
Due to their formidable size and power, gaurs have few natural enemies besides humans. Leopards (Panthera pardus) and dhole (Cuon alpinus) packs occasionally attack unguarded calves or unhealthy animals, but only thetiger (Panthera tigris) and the saltwater crocodile (Crocodylus porosus) have been reported to kill a full-grown adult. The habitat of gaurs and saltwater crocodiles seldom overlaps in recent times due to the decreasing range of both species. Tigers hunt young or infirm gaur, but have been reported to have also killed healthy bulls weighing at least 1,000 kg (2,200 lb). When confronted by a tiger, the adult members of a gaur herd often form a circle surrounding the vulnerable young and calves, shielding them from the big cat. A herd of gaur in Malaysia encircled a calf killed by a tiger and prevented it from approaching the carcass. In Nagarahole National Park, upon sensing a stalking tiger, a herd of gaur walked as a menacing phalanx towards it, forcing the tiger to retreat and abandon the hunt. Gaur are not as aggressive toward humans as wild water buffaloes.
A video of a tiger killing a female gaur was recorded in the Bandipur Tiger Reserve in October 2013.
Threats
In Laos, gaurs are highly threatened by poaching for trade to supply international markets, but also by opportunistic hunting, and specific hunting for home consumption. In the 1990s, they were particularly sought by Vietnamese poachers for their commercial value.
In Thailand, gaurs are highly threatened by poaching for commercial trade in meat and trophies.
Conservation
In captivity
• On 2 August 2011, a 17-year old male gaur named "Mani" was found gored to death in his enclosure, by a younger male allegedly over fight for mate at the Arignar Anna Zoological Park, Chennai. The zoo officials reported Mani was the oldest of the herd of gaur living in the zoo, and added that this is an unusual incident.
• On 8 January 2001, the first cloned gaur was born at Trans Ova Genetics in Sioux Center, Iowa. The calf was carried and brought successfully to term by a surrogate mother, adomestic cow (Bos taurus). While healthy at birth, the calf died within 48 hours of a common dysentery, most likely unrelated to cloning.