WILD YAK

Bos grunniens or Bos mutus

Physical Description

The Wild Yak is the ancestor of the domestic yak that Tibetans have relied upon for centuries. Yaks belong to the Bovini tribe, which also includes bisons, buffaloes, and cattle. Though there are over 12 million domestic yaks in the Central Asian highlands, fewer than 10,000 Wild yaks survive. The only zoo in the world that has a Wild yak is in China. Wild yaks are larger and shier than domestic yaks and their coats are usually a different color.

Domestic yaks are usually solid white, grey, or brown, or black with patches of white, grey, and brown. The Wild Yak, on the other hand, is typically solid black, with rust-brown overtones, and is very rarely golden. Young Wild yaks are dark brown.

The Wild Yak has a grey area above the tip of its muzzle. The Wild Yak’s coat has an inner layer of dense, short, wooly fur beneath coarse guard hairs. A long fringe of hair grows from the Yak’s lower neck, chest, sides, and thighs. The Wild Yak has a large, bushy tail.

The Wild Yak’s horns are grey to black and curve outwards, forwards, back, and slightly inward. The horns of males are larger than those of females. The horns of male Wild yaks average 42.6 centimetres (16.8 inches) in length, from tip-to-tip, and 35.2 centimetres (13.9 inches) in circumference. The horns of females average 32.2 centimetres (12.7 inches) from tip-to-tip and 19.5 centimetres (7.68 inches) in circumference.

The Wild Yak’s thick coat and its relatively small number of sweat glands help the Yak to conserve heat. The Yak can tolerate temperatures as low as minus 40 degrees Celsius. The Wild Yak’s large lungs and its blood’s high red blood cell count and high concentration of hemoglobin enable the Yak to do well at high altitudes. The Wild Yak’s broad hooves and strong legs allow it to adeptly climb steep, rocky slopes. The Wild Yak has poor eyesight, but this is compensated for with its well-developed sense of smell and outstanding hearing. The Yak responds to sounds several kilometres away.

The Yak has a hump just behind its neck. Males are larger than females. Wild yak males measure 175 to 203 centimetres (5.7 to 6.6 feet) tall at the shoulder and 358 to 381 centimetres (11.7 to 12.5 feet) long. Females, in contrast, measure 137 to 156 centimetres (4.5 to 5.1 feet) tall and average 305 centimetres (10 feet) long. Wild yaks weigh between 300 and 1000 kilograms (660 to 2,200 pounds).

 

Habitat

The Wild Yak inhabits treeless plains, hills, and mountains, from 3,200 to 5,400 metres (10,500 to 17,700 feet) in elevation. The Yak generally avoids arid and warm areas, preferring alpine meadows, and, to a lesser extent, the alpine steppe. The Wild Yak migrates from lower to higher elevations for the warmest months of the year, August and September.

The Wild Yak is endemic to the Tibetan Plateau. The Wild Yak could be found almost everywhere in Tibet prior to 1949. Today, the Wild Yak is mostly confined to the remote northwestern part of the Tibetan Plateau, including North and Northwest Tibet and the southern fringes of the Xinjiang Uygur Autonomous Region. The highest concentration of Wild yaks is found within the 284,000 square-kilometer Chang Tang Nature Reserve. A few Wild yaks seasonally migrate into Ladakh and, possibly, into northern Nepal.

 

Eating Habits

The herbivorous Wild Yak eats grasses, sedges, herbs, and, occasionally, lichens and tubers. In the summer, the Yak drinks water frequently. In the winter, the Wild Yak eats snow to hydrate itself.

 

Behaviour and Reproduction

The Wild Yak is active during the day. The Yak spends most of its time browsing, often travelling considerable distances. Wild Yak males are often found alone or in all-male herds. Females are usually found in all-female herds or mixed herds. The size of herds ranges from about five yaks to above 100 yaks. Females are usually found on higher, more protected slopes than the males.

The Wild Yak reaches sexual maturity between four to six years of age, but females may begin breeding at just 3 years of age. The Wild Yak’s rut occurs from July to September. During this season, yaks may be heard making one of their few vocalizations, a grunting noise. The Wild Yak’s gestation period is 258 to 270 days. Most births take place between April and June. Each dri mother gives birth to one calf. Wild yak calves are able to stand immediately after birth and learn how to walk within a few hours. Mothers wean their calves after a year and calves grow to adult size by two years of age.

The Wild Yak lives for a maximum of 25 years. The Yak’s only natural predator is the wolf. Wild yaks flee from danger, often up steep slopes, and as far away from the threat as 20 kilometres (12 miles). Yaks also use their massive horns to defend themselves. Wild yaks in herds sometimes respond to the approach of a predator by huddling closely together, with the yaks on the outside of the circle lowering their horns as if ready to attack. Wild yaks will also try to scare predators away by charging.

 

Present Status

The Wild Yak is categorized as Vulnerable in the 2003 IUCN Red List of Threatened Species and is listed under Appendix I of CITES. The Yak is under first class protection in China and is included in Schedule II, Part I of the Indian Wild Life (Protection) Act of 1972. The Wild Yak’s population has declined at least 20% of the last 20 years. In 1995, the number of Wild yaks was estimated at around 15,000. Today, probably fewer than 10,000 mature Wild yaks remain.

 

Threats to Survival

The most serious threat to the Wild Yak’s survival is casual and market hunting. The Yak is hunted for its meat, horns, and other materials. It is illegal to kill a Wild yak in Tibet without a permit from the government, but because the regions where Wild yaks are found are so remote, it is difficult for officers to enforce this law. Male yaks tend to be easier targets than females because they inhabit more open terrain.

The spread of pastoralists and their livestock into areas of Tibet that were previously uninhabited by humans poses additional problems for the Wild Yak. Wild yaks in areas encroached upon by pastoralists now have to compete with livestock for pasture. In other cases, pastoralists may build fences and simply shut the Wild Yak out of its previous grazing lands. Wild yaks have also contracted viral and bacterial diseases from livestock, such as Brucellosis, which can result in spontaneous abortion. Furthermore, Wild yaks may interbreed with domestic yaks, resulting in hybridization. Other areas of the Wild Yak’s habitat have been degraded as a result of mining operations.

 

References

Hedges, S., 2000: Bos grunniens. In: IUCN, 2003: 2003 IUCN Red List of Threatened Species, http://www.redlist.org, Aug 2004.

Huffman, Brent, March 2004: Yak, http://www.ultimateungulate.com/Artiodactyla/Bos_grunniens.html, Sept 2004.

Oliphant, M., 2003: Bos grunniens, Animal Diversity Web, http://animaldiversity.ummz.umich.edu/site/accounts/information/

Bos_grunniens.html, Sept 2004.

Sathyakumar, S., and Bhatnagar, Y.V., eds., 2002: Mountain Ungulates, ENVIS Bulletin: Wildlife and Protected Areas, Vol. 1, No. 1, http:/

/www.wii.gov.in/envis/ungulates/chapter2.htm, Sept 2004.

Schaller, George B., 1998: Wildlife of the Tibetan Steppe, The University of Chicago Press, London.

UNEP World Conservation Monitoring Centre, Oct 2001: Wild Yak – Bos grunniens, http://www.unep-wcmc.org/species/data/

species_sheets/yak.htm, Sept 2004.

By: Environment and Development Desk, DIIR, CTA.