The YAK (Bos grunniens and Bos mutus) is a long-haired bovine found throughout the Himalayan region of south Central Asia, the Tibetan Plateau and as far north as Mongolia and Russia. Most yaks are domesticated animals, usually referred to as Bos grunniens. There is also a small, vullnerable wild yak population, referred to as Bos mutus. In the 1990s, a concerted effort was undertaken to help save the wild yak population.
The English word "yak" derives from the Tibetan 'g.yag' or 'gyag' - in Tibetan this refers only to the male of the species, the female being called a 'dri' or 'nak'. In English, as in most other languages which have borrowed the word, 'yak' is usually used for both sexes.
Yaks belong to the genus Bos, and are therefore related to cattle. Mitochondrial DNA analyses to determine the evolutionary history of yaks have been somewhat ambiguous. The yak may have diverged from cattle at any point between one and five million years ago, and there is some suggestion that it may be more closely related to bison than to the other members of its designated genus. Apparent close fossil relative of the yak, such as Bos baikalensis, have been found in eastern Russia, suggesting a possible route by which yak-like ancestors of the modern American bison could have entered the Americas.
Yak physiology is well adapted to high altitudes, having larger lungs and heart than cattle found at lower altitudes, as well as greater capacity for transporting oxygen through their blood due to the persistence of foetal haemoglobin throughout life. Conversely they do not thrive at lower altitudes and begin to suffer from heat exhaustion above about 15C (59F). Further adaptations to the cold include a thick layer of subcutaneous fat and an almost complete lack of sweat glands.
Yaks mate in the summer, typically between July and September, depending on the local environment. For the remainder of the year, many males wander in small bachelor groups away from the large herds, but as the rut approaches, they become aggressive and regularly fight each other to establish dominance. In addition to non-violent threat displays, bellowing, and scraping the ground with their horns, male yaks also compete more directly, repeatedly charging at each other with heads lowered or sparring with their horns. Like bison, but unlike cattle, males wallow in dry soil during the rut, often while scent-marking with urine or dung. Females enter oestrus up to four times a year, and are receptive only for a few hours in each cycle.
Gestation lasts between 257 and 270 days, so the young are born between May and June, and results in the birth of a single calf. The female finds a secluded spot to give birth but the calf is able to walk within about 10 minutes of birth and the pair soon rejoin the herd. Calves are weaned at one year and become independent shortly afterwards. Wild calves are initially brown in colour and only later develop the darker adult hair. Females generally give birth for the first time at three or four years of age and reach their peak reproductive fitness at around six years. Yaks may live for more than 20 years in domestication or captivity, although it is likely this may be somewhat shorter in the wild.
Contrary to popular belief, yaks and their manure have little to no detectable odour when maintained appropriately in pastures or paddocks with adequate access to forage and water. Yak's wool is naturally odour resistant.
I have found some interesting information about the wild yak which has quite fascinated me and I will continue this in part 2 of the yak story.