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Tibetan yaks have fur ranging from brown to black in color. They have large horns that curve upward and long hair covering the body and tail. Domesticated Tibetan yaks differ from their wild counterparts in that they have shorter legs, wider hooves, more variations to fur color, and weaker horns. Both sexes have horns, with females having smaller horns.
Almost without exception, the Tibetan yaks seen in zoos (and here at the Alaska Zoo) are the domesticated variety. They are raised on farms for meat and used as pack animals for mountaineering in some cases.
Wild yaks spend most of their time grazing, living in herds from 20 to 200 individuals. Herds move down from alpine areas in July to feed along plateaus and then up in the mountains again in August as temperatures rise. They are always on the move to find plants due to the sparse vegetation in their alpine habitat. Tibetan yaks are very cold tolerant. During severe winter cold, yaks carry on and have even been seen bathing in lakes or streams in frigid temperatures. If a herd is disturbed, they will run for a long distance with tails held up in the air. They will bluff attack if a threat is in their path of travel. They are mainly active during the day.
Both wild and domesticated yaks possess large lungs, a high red blood cell count, and a higher concentration of hemoglobin than most other bovids. All of these factors allow the Tibetan yak to live and thrive in high, oxygen-deprived elevations that other animals could not tolerate.
In spite of their bulky appearance, yaks arequick on their feet and are excellent and sure-footed climbers. One of the few vocalizations they make is a loud grunt, made during the breeding season by wild yaks. Domestic yaks, however, "grunt" throughout the year. This grunting sound earned Tibetan yaks the scientific name "grunniens".
Yaks are grazers, with a diet composed mainly of various low-lying grasses and grass-like plants, including shrubs, forbs, etc., found on the Tibetan plateau. They will also consume lichen, mosses, tubers, and forbs.
During the mating season, males leave their groups and join the female herds. Males compete for access to receptive females, often violently. The mating season starts in September, with births usually occurring in June. In the wild, females have one calf every other year. Gestation is about nine months, weaning occurs at one year, and full size and sexual maturity is reached in six to eight years. For the domesticated yak, the reproductive cycle is more varied with the female sometimes giving birth to more than one calf per year. Most of the parental care is done by the female. Young are born able to stand and walk within several hours after birth.
Wild Tibetan yaks are listed as a Vulnerable species by the IUCN. There are many factors that are currently leading to a decline in the number of wild yak, which is currently estimated at around 15,000. Perhaps one of the largest has been hunting by humans. The introduction of domesticated yaks also presents problems in regards to the transmission of disease (e.g. brucellosis), and possible increased competition for the same grazing land.