The yak is a bovine with long hair. Wild male yaks are about 2–2.2 meters at the shoulder, females about 1 meter. Yaks of the domestic sort are shorter, both males and females being 1 - 2 meters. The long, thick hair of yaks keeps them warm. Wild yaks are mostly black or brown, though some are grey, white, roan or piebald.
Domesticated yaks are found in the Himalayan region in southern Central Asia, on the Tibetan Plateau and also as far north as Russia and Mongolia. Wild yaks are mostly found in western Qinghai and northern Tibet, with some populations in the very south of Xinjiang, and in Ladakh in India. Small populations of wild yak can be found in eastern Qinghai, western Tibet and Sichuan nearer to Huanglong.
Yaks are a social animal which gathers in herds numbering over 100 individuals, though groups of 10–20 are also common. Adult males will often travel with females and their young, although older males may form groups of 2–5, traveling separately from maternal herds. After the mating period bulls will separate themselves from the herd, climbing to the most remote areas high in the mountains, either alone or with other bulls. Researchers have noted that wild yaks in the Tibetan mountains will graze separately during winter until spring.
Mating takes place mostly in mid-July. Solitary bulls will return to the herd at this time. If several bulls return at the same time, fighting may occur, competing to be the dominant animal in the herd. Frightened or defeated bulls don't give up the competition; but leave for 2-3 days grazing and then return to fight again. Bulls mostly associate with one cow only during the mating season. The gestation period is between 257 to 270 days. Females typically give birth once every other year to only one calf. The calf can walk about ten minutes after being born. Weaning takes place at one year and calves become independent soon after.
Uncontrolled hunting is a major threat for wild yak. 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 population is concentrated in Chang Tang Reserve in Tibet. The population in India is a maximum of around 110 wild yaks in Ladakh region. The ICUN classifies the wild yak as "Vulnerable", with a decreasing population trend.
Yaks are among the most important domesticated animals in central Asia. Their great ability to survive at high altitudes contributed to making human settlement of the Tibetan Plateau possible. They provide meat, milk, pack energy and, dung, the latter most important in the arid, cool climate, being a critical factor for colonization in this region. The yak is thought to have been domesticated during the first millennium B.C in Tibet. Currently in Central Asia's highlands there are over 14 million domestic yaks.