The ancestor of the wild and domestic yak is thought to have diverged fromBos primigenius at a point between one and five million years ago.[2] The wild yak is now normally treated as a separate species from the domestic yak (Bos grunniens).[3] Based on genomic evidence, the closest relatives of yaks are considered to bebison, which have historically been considered members of their own titular genus, rendering the genusBos paraphyletic.[4]
Relationships of members of the genusBos based on nuclear genomes after Sinding, et al. 2021.[5]
The wild yak is among the largest extant bovid species. Adults stand about 1.6 to 2.05 m (5.2 to 6.7 ft) tall at the shoulder, and weigh 500–1,200 kg (1,100–2,600 lb). The head and body length is 2.4 to 3.8 m (7.9 to 12 ft), not counting the tail of 60 to 100 cm (24 to 39 in).[6] The females are about one-third the weight and are about 30% smaller in their linear dimensions when compared to bull wild yaks. Domesticated yaks are somewhat smaller.[7][8][9][10]
They are heavily built animals with a bulky frame, sturdy legs, and rounded cloven hooves. To protect against the cold, theudder in females and thescrotum in males are small, and covered in a layer of hair. Females have fourteats. 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, rather than tufted like the tails of cattle orbison. 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 coloured hair are known as the wild golden yak (Chinese:金色野牦牛;pinyin:jīnsèyě máoniú). They are considered an endangered subspecies in China, with an estimated population of 170 left in the wild.[11]
Two morphological types have been identified, so-calledQilian andKunlun.[6]
Wild yaks once ranged up to southernSiberia to the east ofLake Baikal,[12] with fossil remains of them being recovered fromDenisova Cave,[13] but became extinct in Russia around the 17th century.[14] Today, wild yaks are found primarily in northernTibet and westernQinghai, with some populations extending into the southernmost parts ofXinjiang, and intoLadakh in India. Small, isolated populations of wild yak are also found farther afield, primarily in western Tibet and eastern Qinghai. In historic times, wild yaks were also found inBhutan, but they are now considered extinct there.[1]
The primary habitat of wild yaks consists of treeless uplands between 3,000 and 5,500 m (9,800 and 18,000 ft), dominated by mountains andplateaus. They are most commonly found inalpine tundra with a relatively thick carpet of grasses and sedges rather than the more barrensteppe country.[15]
The wild yak was thought to be regionally extinct inNepal in the 1970s, but was rediscovered inHumla in 2014.[16][17] This discovery later resulted in the species being added to Nepal's currency.[18]
A painting of a wild yak, published byRowland Ward LTD in 1898.
The diet of wild yaks consists largely of grasses and sedges, such asCarex,Stipa, andKobresia. They also eat a smaller amount of herbs,winterfat shrubs, and mosses, and have even been reported to eatlichen. Historically, the main natural predator of the wild yak has been theHimalayan wolf, butHimalayan black bears,Himalayan brown bears andsnow leopards have also been reported as predators in some areas, likely of young or infirm wild yaks.[11]
Before long I was to see the vast herds of drongs with my own eyes. The sight of those beautiful and powerful beasts who from time immemorial have made their home onTibet's high and barren plateaux never ceased to fascinate me. Somehow these shy creatures manage to sustain themselves on the stunted grass roots which is all that nature provides in those parts. And what a wonderful sight it is to see a great herd of them plunging head down in a wild gallop across the steppes. The earth shakes under their heels and a vast cloud of dust marks their passage. At nights they will protect themselves from the cold by huddling up together, with the calves in the centre. They will stand like this in a snow-storm, pressed so close together that the condensation from their breath rises into the air like a column of steam. The nomads have occasionally tried to bring up young drongs as domestic animals, but they have never entirely succeeded. Somehow once they live together with human beings they seem to lose their astonishing strength and powers of endurance; and they are no use at all aspack animals, because their backs immediately get sore. Their immemorial relationship with humans has therefore remained that of game and hunter, for their flesh is very tasty.
Wild yaks areherd animals. 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. On average female yaks graze 100m higher than males. Females with young tend to choose grazing ground on high, steep slopes.[20] The remaining males are either solitary, or found in much smaller groups, averaging around six individuals. Groups move into lower altitude ranges during the winter.[1] Although wild yaks can become aggressive when defending young, or during therut, they generally avoid humans, and may flee for great distances if approached.[11]
The wild yak is currently listed asVulnerable on theIUCN Red List. It was previously classified asEndangered, but was downlisted in 1996 based on the estimated rate of population decline and current population sizes. The latest assessment in 2008 suggested a total population of no more than 10,000 mature individuals.[1]
The wild yak is experiencing threats applied by several sources. Poaching, including commercial poaching, has remained the most serious threat; males are particularly affected because of their more solitary habits. Disturbance by and interbreeding with livestock herds is also common. This may include the transmission of cattle-borne diseases, although no direct evidence of this has yet been found. Conflicts with herders themselves, as in preventive and retaliatory killings for abduction of domestic yaks by wild herds, also occur but appear to be relatively rare. Recent protection from poaching particularly appears to have stabilized or even increased population sizes in several areas, leading to the IUCN downlisting in 2008. In both China and India, the species is officially protected; in China it is present in a number of large nature reserves.[1]
^abHan Jianlin, M. Melletti, J. Burton, 2014, Wild yak (Bos mutus Przewalski, 1883), Ecology, Evolution and Behavior of Wild Cattle: Implications for Conservation, Chapter 1, p.203,Cambridge University Press
^Stanley J. Olsen, 1990, Fossil Ancestry of the Yak, Its Cultural Significance and Domestication in Tibet, p.75, Proceedings of the Academy of Natural Sciences of Philadelphia,Academy of Natural Sciences of Drexel University
^Daniel J Miller, Gui Quan. Cai, Richard B. Harris, 1994, Wild yaks and their conservation on the Tibetan plateau, Ecology, Evolution and Behavior of Wild Cattle: Implications for Conservation, Chapter 12, Cambridge University Press
^Tibet is My Country: Autobiography of Thubten Jigme Norbu, Brother of the Dalai Lama as told to Heinrich Harrer, p. 151. First published in German in 1960. English translation by Edward Fitzgerald, published 1960. Reprint, with updated new chapter, (1986).Wisdom Publications, London.ISBN0-86171-045-2.
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