Perception Channels: tactile ; chemical
There are many factors that are currently leading to a decline in the number of wild B. grunniens, which is currently estimated at around 15,000. Perhaps one of the largest has been hunting by humans. According to Schaller and Wulin (1995), while the Tibet Forest Bureau is making substantial efforts to protect yak (including fines of up to $600), "Hunting is difficult to suppress without a mobile patrol force, as the recent decimation of wildlife in the Arjin Shan Reserve has shown."
Also, as pastoralists are starting to change their habits from a nomadic to sedentary lifestyle their habit is beginning to become fenced off. The introduction of domesticated yaks (via the pastoralists) also presents problems in regards to the transmission of disease (e.g. brucellosis), and possible increased competition for the same grazing land (Schaller & Wulin, 1995).
Domesticated yak are not listed as endangered due to their large numbers.
US Federal List: endangered
CITES: appendix i; no special status
There are several negative economic impacts on humans. Where wild and domesticated B. grunniens live in close proximity to one another, wild yak have been known to break down fences. In some extreme circumstances, wild yaks have been known to kill domesticated yak (Buchholtz, 1990).
The possibility of the transmission of disease between domestic and wild B. grunniens is also a concern in areas where the two live fairly close to one another, and perhaps have limited contact (Schaller & Wulin, 1996).
Negative Impacts: causes or carries domestic animal disease
Domestic:
With wide hooves and the ability to carry large weights at high elevations, domesticated yak serve as beasts of burden for many inhabitants of the Tibetan plateau. The finer fur of the young is used for clothing, while the longer fur of the adult is used in making blankets, tents, etc. Also, in some areas where firewood is particularly sparse, the dung is used as fuel. In some areas, milk from the cow is used to produce large amounts of butter and cheese for export (Buchholtz, 1990).
Wild:
The wild counterpart of B. grunniens serves many of the same economic functions, although to a lesser degree due to their rather sparse availability and obvious non-domestication. While penalties have been set by China, hunting of the wild yak still takes place, especially in the winter where some local farmers find them the only source of meat during harsh winter months (Schaller & Wulin, 1996).
Positive Impacts: food ; body parts are source of valuable material; produces fertilizer
Through their grazing activities, yaks play an important role in nutrient recycling and in generating intermediate levels of disturbance in their ecosystems. They are also an important prey species for wolves.
Bos grunniens is a grazer, with a diet composed mainly of various low-lying grasses and grass-like plants, including shrubs, forbs, cushion plants, etc., found on the Tibetan plateau, though they will also consume lichen, mosses, and forbs (Schaller & Wulin, 1995).
Plant Foods: leaves; bryophytes; lichens
Primary Diet: herbivore (Folivore )
While their domesticated counterparts can be found in a much more varied area in the oriental region, the main geographic range of wild B. grunniens is limited to the Tibetan Plateau, which includes "...the western edge of Gansu Province, Qinghai Province, the southern rim of the Xinjiang Autonomous Region, and the Tibet Autonomous Region." (Schaller & Wulin, 1995).
Biogeographic Regions: palearctic (Native ); oriental (Native )
The habitat of B. grunniens can vary, but mainly consists of three areas with different vegetation: Alpine meadow, alpine steppe, and desert steppe (Schaller & Wulin, 1996). Each habitat features large areas of grassland, but differ in the type of grasses/small shrubs, amount of vegetation, average temperature, and precipitation.
The habitat for B. grunniens can also be dependent on the season. Some herds will migrate large distances seasonally to feed on grass, moss, and lichens. However, B. grunniens by most accounts does not care for warm weather and, preferring the colder temperatures of the plateaus, will return when seasonal temperatures start to warm (Buchholtz, 1990).
In more recent years, B. grunniens has been increasingly confined to the desert steppe. This is in part due to the fact that farmers moving into the region don't find the land and minimal precipitation (50-100 mm/yr) desirable. Yaks are thus not disturbed by human activities in this region (Schaller & Wulin, 1996).
Range elevation: 3200 to 5400 m.
Average elevation: 4500 m.
Habitat Regions: temperate ; polar ; terrestrial
Terrestrial Biomes: tundra ; mountains
In the wild, the maximum lifespan of B. grunniens is limited to about 25 years.
Range lifespan
Status: wild: 25 (high) years.
Average lifespan
Sex: female
Status: wild: 25.0 years.
Wild yak males can be up to 3,250 mm in length and more than 2,000 mm in height. Average weight for male B. grunniens is 1,000 kg with the female being around 300 kg (Nowak, 1999). Domestic yaks can be considerably smaller in weight, with males ranging from 350 to 580 kg and females between 225 to 255 kg (Buchholtz, 1990).
Other physical features of B. grunniens include: a blackish brown pelage, large black upward curving horns, and long hair covering the body including the tail (Nowak, 1999). In contrast, domesticated populations have shorter legs, broader hooves, more varied pelage coloration, and weaker horns which sometimes can be absent altogether (Buchholtz, 1990).
Both wild and domesticated yaks possess large lungs, a high red blood cell count, and higher concentration of hemoglobin than most other bovids. All of these factors allow the yak to live and thrive in higher elevations that would give other, non-acclimated animals elevation sickness (Summers, 1997).
Range mass: 300 to 1000 kg.
Range length: 3250 (high) mm.
Other Physical Features: endothermic ; bilateral symmetry
At signs of danger, wild herds of B. grunniens will run from the threat. Other actions that they will take include loud snorting and charging at the perceived threat (Buchholtz, 1990).
Known Predators:
For most of the year, male and female wild yaks spend their time in separate herds. While females and young (occasionally including some young males) usually stay in large herds, males tend to either spend their time alone or in small groups. During the mating season, males leave their groups and join with the female herds. Males compete for access to receptive females, often violently. (Nowak, 1999; Buchholtz, 1990)
Mating System: polygynous
The mating season for B. grunniens starts in September, with births usually occuring in June (Buchholtz, 1990).
In the wild, the female B. grunniens have one calf every other year. Gestation is about 9 months, weaning occurs at one year, and full size is obtained in 6-8 years. At this age sexual maturity is also attained. For the domesticated yak the reproductive cycle is more varied, with the cow sometimes giving birth to more than one calf per year (Nowak, 1999).
Breeding season: In wild yak the mating season begins in September, with births occurring in June (Nowak, 1999).
Range number of offspring: 1 (low) .
Average number of offspring: 1.
Average gestation period: 9.33 months.
Range weaning age: 5 to 9 months.
Range age at sexual or reproductive maturity (female): 6 to 8 years.
Range age at sexual or reproductive maturity (male): 6 to 8 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); viviparous
Average birth mass: 18000 g.
Average gestation period: 274 days.
Average number of offspring: 1.
Most of the parental care of young is done by the female due to the nature of wild female and male B. grunniens to spend the majority of the year in separate groups (Buchholtz, 1990). Young are born able to stand and walk within several hours after birth.
Parental Investment: altricial ; female parental care
The domestic yak (Bos grunniens), also known as the Tartary ox, grunting ox[1] or hairy cattle,[2] is a species of long-haired domesticated cattle found throughout the Himalayan region of the Indian subcontinent, the Tibetan Plateau, Gilgit-Baltistan (Kashmir), Tajikistan and as far north as Mongolia and Siberia. It is descended from the wild yak (Bos mutus).[3]
The English word "yak" originates from the Tibetan: གཡག་, Wylie: g.yag. In Tibetan and Balti it refers only to the male of the species, the female being called Tibetan: འབྲི་, Wylie: bri, Tibetan: འབྲི་, Wylie: dri or Tibetan: གནག, Wylie: g.nag in Tibetan and Tibetan: ཧཡག་མོ་, Wylie: hYag-mo in Balti. In English, as in most other languages that have borrowed the word, "yak" is usually used for both sexes, with "bull" or "cow" referring to each sex separately.
Belonging to the genus Bos, Yaks are related to cattle (Bos primigenius). Mitochondrial DNA analyses to determine the evolutionary history of yaks have been inconclusive.
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.[4] Apparent close fossil relatives 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.[5]
The species was originally designated as Bos grunniens ("grunting ox") by Linnaeus in 1766, but this name is now generally considered to refer only to the domesticated form of the animal, with Bos mutus ("mute ox") being the preferred name for the wild species. Although some authors still consider the wild yak to be a subspecies, Bos grunniens mutus, the ICZN made an official ruling in 2003[6] permitting the use of the name Bos mutus for wild yaks, and this is now the more common usage.[7][5][8]
Except where the wild yak is considered as a subspecies of Bos grunniens, there are no recognised subspecies of yak.
Yaks are heavily built animals with bulky frames, sturdy legs, rounded, cloven hooves, and extremely dense, long fur that hangs down lower than the belly. While wild yaks are generally dark, blackish to brown in colouration, domestic yaks can be quite variable in colour, often having patches of rusty brown and cream. They have small ears and wide foreheads, with smooth horns that are generally dark in colour. In males (bulls), the horns sweep out from the sides of the head, and then curve backward; they typically range from 48 to 99 cm (19 to 39 in) in length.
The horns of females (cows) are smaller, at 27 to 64 cm (11 to 25 in) in length, and have a more upright shape. Both sexes have a short neck with a pronounced hump over the shoulders, although this is larger and more visible in males.[5] Males weigh 350 to 585 kg (772 to 1,290 lb), females weigh 225 to 255 kg (496 to 562 lb). Wild yaks can be substantially heavier, bulls reaching weights of up to 1,000 kilograms (2,200 lb).[9] Depending on the breed, domestic yak males are 111–138 centimetres (44–54 in) high at the withers, while females are 105–117 centimetres (41–46 in) high at the withers.[10]
Both sexes have long shaggy hair with a dense woolly undercoat over the chest, flanks, and thighs to insulate them from the cold. Especially in bulls, this may form a long "skirt" that can reach the ground. The tail is long and horselike rather than tufted like the tails of cattle or bison. Domesticated yaks have a wide range of coat colours, with some individuals being white, grey, brown, roan or piebald. The udder in females and the scrotum in males are small and hairy, as protection against the cold. Females have four teats.[5]
Yaks are not known to produce the characteristic lowing (mooing) sound of cattle, but both wild and domestic yaks grunt and squeak, which inspired the scientific name of the domestic yak variant, Bos grunniens (grunting bull). Nikolay Przhevalsky named the wild variant Bos mutus (silent bull) believing that it did not make a sound at all, but it does.[11]
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,[12][13] due to the persistence of foetal haemoglobin throughout life.[14] Conversely, yaks have trouble thriving at lower altitudes,[15] and are prone to suffering from heat exhaustion above about 15 °C (59 °F). Further adaptations to the cold include a thick layer of subcutaneous fat, and an almost complete lack of functional sweat glands.[12]
Compared with domestic cattle, the rumen of yaks is unusually large, relative to the omasum. This likely allows them to consume greater quantities of low-quality food at a time, and to ferment it longer so as to extract more nutrients.[12] Yak consume the equivalent of 1% of their body weight daily while cattle require 3% to maintain condition. They are grazing herbivores, with their wild ancestors feeding primarily on grass and sedges,[16] with some herbs and dwarf shrubs.[17]
Yaks mate in the summer, typically between July and September, depending on the local environment. For the remainder of the year, many bulls wander in small bachelor groups away from the large herds, but, as the rut approaches, they become aggressive and regularly fight among each other to establish dominance. In addition to non-violent threat displays, bellowing, and scraping the ground with their horns, bull 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.[5] Females enter oestrus up to four times a year, and females are receptive only for a few hours in each cycle.[18]
Gestation lasts between 257 and 270 days,[12] so that the young are born between May and June, and results in the birth of a single calf. The cow finds a secluded spot to give birth, but the calf is able to walk within about ten minutes of birth, and the pair soon rejoin the herd.[12] Females of both the wild and domestic forms typically give birth only once every other year,[5] although more frequent births are possible if the food supply is good.
Calves are weaned at one year and become independent shortly thereafter. Wild calves are initially brown in color, and only later develop the darker adult hair. Females generally give birth for the first time at three or four years of age,[19] and reach their peak reproductive fitness at around six years. Yaks may live for more than twenty years in domestication or captivity,[5] although it is likely that this may be somewhat shorter in the wild.
Domesticated yaks have been kept for thousands of years, primarily for their milk, fibre and meat, and as beasts of burden. Their dried droppings are an important fuel, used all over Tibet, and are often the only fuel available on the high treeless Tibetan Plateau. Yaks transport goods across mountain passes for local farmers and traders and are an attraction for climbing and trekking expeditions: "Only one thing makes it hard to use yaks for long journeys in barren regions. They will not eat grain, which could be carried on the journey. They will starve unless they can be brought to a place where there is grass."[20] They also are used to draw ploughs.[21] Yak's milk is often processed to a cheese called chhurpi in Tibetan and Nepali languages, and byaslag in Mongolia. Butter made from yaks' milk is an ingredient of the butter tea that Tibetans consume in large quantities,[22] and is also used in lamps and made into butter sculptures used in religious festivities.[23]
Small numbers of herds can be found in the United States and Canada, as well as New Zealand and some parts of Europe. Yaks have generated interest outside the Himalayas as a commercial crop and by cattle breeders. The main interest of North American yak breeders is lean meat production by "hybridizing" with other cattle, followed by yak fiber wool production.[24]
The Indian government established a dedicated centre for research into yak husbandry, the ICAR-National Research Centre on Yak, in 1989. It is located at Dirang, Arunachal Pradesh, and maintains a yak farm in the Nyukmadung area at an altitude of 2,750 metres (9,020 ft) above MSL.[25]
In Nepal, Tibet and Mongolia, domestic cattle are crossbred with yaks. This gives rise to the infertile male dzo མཛོ། as well as fertile females known as མཛོ་མོ། dzomo or zhom, which may be crossed again with cattle. The "Dwarf Lulu" breed, "the only Bos primigenius taurus type of cattle in Nepal" has been tested for DNA markers and found to be a mixture of both taurine and zebu types of cattle (B. p. taurus and B. p. indicus) with yak.[26] According to the International Veterinary Information Service, the low productivity of second generation cattle-yak crosses makes them suitable only as meat animals.[27]
Crosses between yaks and domestic cattle (Bos primigenius taurus) have been recorded in Chinese literature for at least 2,000 years.[5] Successful crosses have also been recorded between yak and American bison,[27] gaur, and banteng, generally with similar results to those produced with domestic cattle.[5]
Jacques et al. (2021)[28] show that most elaborate yak-related terminologies are found within Tibetic and Gyalrongic languages. Both branches also have native terms for yak-cattle hybrids, suggesting that Tibetic and Gyalrongic speakers may have independently cross-bred yaks and cattle, predating the proto-Gyalrongic split (3221 [2169-4319] BP[29]) from Tibeto-Gyalrongic.
In Nepal, there is an annual festival held to drink fresh blood of yak in a belief that it cures varieties of disease such as gastritis, jaundice and body sprain.[30][31] The fresh blood is extracted from the neck of a yak without killing it. The cut is healed after the ceremony is over.[32] The ritual is believed to be originated in Tibet and Mustang.[33]
In parts of Tibet and Karakorum, yak racing is a form of entertainment at traditional festivals and is considered an important part of their culture. More recently, sports involving domesticated yaks, such as yak skiing or yak polo, are being marketed as tourist attractions in South Asian countries, including in Gilgit-Baltistan, Pakistan.
Yaks in Manali, Himachal Pradesh, India saddled for riding
Train of pack yaks at Litang monastery in Garzê Tibetan Autonomous Prefecture, Sichuan, China
Yaks plowing fields in Tibet
A Tibetan Yak in Russia
Yaks in Gilgit-Baltistan, Pakistan
Domestic yak in Mao County, China
Girl on Yak in Yunnan Province, China
A yak at Mount Siguniang Scenic Area, Sichuan, China
The domestic yak (Bos grunniens), also known as the Tartary ox, grunting ox or hairy cattle, is a species of long-haired domesticated cattle found throughout the Himalayan region of the Indian subcontinent, the Tibetan Plateau, Gilgit-Baltistan (Kashmir), Tajikistan and as far north as Mongolia and Siberia. It is descended from the wild yak (Bos mutus).
