The ancestor of the wild and domestic yak is thought to havegenetically diverged from theaurochs (Bos primigenius) 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:[5]
The wild yak is heavily built 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, and the coat is typically black or dark brown, covering most of the body, with a grey muzzle. Wild golden-brown individuals have been reported, which are known as the wild golden yak (Chinese:金色野牦牛;pinyin:jīnsèyě máoniú). It is considered an endangered subspecies in China, with an estimated population of 170 wild individuals.[6]Two morphological types have been identified, so-calledQilian andKunlun.[7]
The wild yak is among the largest extant bovid species. Adults stand about 160 to 205 cm (63 to 81 in) tall at the shoulder, and weigh 0.5–1.2 t (0.55–1.32 short tons). The head and body length is 240 to 380 cm (94 to 150 in), not counting the tail of 60 to 100 cm (24 to 39 in).[7] 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.[8][9]
The wild yak once ranged up to southernSiberia to the east ofLake Baikal.[10]Fossil remains were recovered inDenisova Cave.[11] Today, the wild yak occurs primarily in northernTibet and westernQinghai, extending into the southernmost parts ofXinjiang and intoLadakh in India; small, isolated populations of wild yak also live farther afield, primarily in western Tibet and eastern Qinghai.[1] It was thought to be regionally extinct inNepal in the 1970s, but was rediscovered inHumla in 2014.[12]
The primary habitat of the wild yak consists of treeless uplands between 3,000 and 5,500 m (9,800 and 18,000 ft), dominated by mountains andplateaus. It is most common inalpine tundra with a relatively thick carpet of grasses and sedges rather than the more barrensteppe country.[13]
The wild yak is considered extinct inBhutan, and also in Kazakhstan, Mongolia and southern Russia, but it is not certain whether it occurred in these countries after the year 1500.[1]
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.[15] 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.[6]
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]
^abJianlin, H. (2014). "Wild yak (Bos mutus Przewalski, 1883)". In Melleti, M.; Burton, J. (eds.).Ecology, Evolution and Behavior of Wild Cattle: Implications for Conservation. Cambridge:Cambridge University Press. p. 194–215.doi:10.1017/CBO9781139568098.014.
^Boitani, L. (1984).Simon & Schuster's Guide to Mammals. Simon & Schuster, Touchstone Books.ISBN978-0-671-42805-1.
^Olsen, S. J. (1990). "Fossil ancestry of the Yak, its cultural significance and domestication in Tibet".Proceedings of the Academy of Natural Sciences of Philadelphia.142:73–100.JSTOR4064972.
^Norbu, T. J. (1986) [1961].Tibet ist mein Land [Tibet is My Country: Autobiography of the brother of the Dalai Lama as told to Heinrich Harrer] (First, English translation by Edward Fitzgerald ed.). London: Wisdom Publications.ISBN0-86171-045-2.
_BHL9370000.jpg)
