The Wild yak is a large wild bovid native to the Himalayas. They are among the largest bovids and are second only to the gaur in shoulder height. They are also the largest native animal in their range. Wild yaks are heavily built animals with a bulky frame, sturdy legs, and rounded cloven hooves. Both sexes have long shaggy hair with a dense woolly undercoat over the chest, flanks, and thighs for insulation against the cold. In males especially, this undercoat may form a long "skirt" that can reach the ground. The tail is long and horse-like. The coat is typically black or dark brown covering most of the body, with a grey muzzle, although some wild golden-brown individuals have been reported. Wild yaks with gold-colored hair are known as the Wild Golden yak.
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Wild yaks are found primarily in northern Tibet and western Qinghai (Northwestern China), with some populations extending into the southernmost parts of Xinjiang, and into Ladakh in India. Small, isolated populations are also found farther afield, primarily in western Tibet and eastern Qinghai. The primary habitat of Wild yaks consists of treeless uplands, dominated by mountains and plateaus. They are most commonly found in alpine tundra with a relatively thick carpet of grasses and sedges rather than the more barren steppe country.
Wild yaks are social animals that live in herds. Their herds can contain several hundred individuals, although many are much smaller. Herds consist primarily of females and their young, with a smaller number of adult males. Wild yaks are active during the day. On average females graze 100 m higher than males. Females with young tend to choose grazing ground on high, steep slopes. The remaining males are either solitary or gather in smaller groups, averaging around six individuals. Groups move into lower altitude ranges during the winter. Although wild yaks can become aggressive when defending young, or during the rut, they generally avoid humans and may flee for great distances if approached.
Wild yaks are polygynous; this means that males mate with more than one female in a single breeding season. They breed from July to September. Prior to mating, there is a period called "rut". During this time solitary males return to the herd and become highly competitive with each other. If several males return at the same time, fighting may occur, competing to be the dominant animal in the herd. Frightened or defeated males don't give up the competition, but leave for 2-3 days grazing and then return to fight again. Females typically give birth once every other year to only one calf. The gestation period is between 257 to 270 days. Calves are born fully developed and are able to walk about ten minutes after being born. Weaning takes place at one year of age and calves become independent soon after. Young Wild yaks become reproductively mature between 4 to 6 years of age.
Uncontrolled hunting is a major threat to Wild yaks; males are particularly impacted because of their more solitary habits. Disturbance by and interbreeding with livestock herds are also common. Further threats are loss of habitat and diseases from domestic yaks and livestock. The main natural predator was the Tibetan wolf, but snow leopards and brown bears are also predators in some areas.
According to IUCN, as of 2008, the wild yak population is estimated to be at no more than 10,000 mature individuals. The majority of the population is concentrated in Chang Tang Reserve in Tibet. The population in India is a maximum of around 110 individuals in the Ladakh region. Currently, wild yaks are classified as Vulnerable (VU) on the IUCN Red List and their numbers today are decreasing.