Wednesday, 12 October 2011
The wild yak has a dense undercoat of soft, close-matted hair which is covered by generally dark brown to black outer hair. Its long, shaggy coat reaches almost to the ground. The wild yak can weigh up to 1000 kg (2200 lb) with a shoulder height of over 2 m (6.5'). It occurs in treeless uplands, including plains, hills, and mountains, from as low as 3200 m (10,500') up to the limit of vegetation at about 5400 m (18,000'). It stays in high areas with permanent snow during the warmer months of August and September, and spends the rest of the year at lower elevations. The wild yak grazes on grasses, herbs and lichens. Ordinarily it gathers in groups of 10 - 30 or more, but it may occasionally be observed in large groups of 100 - 200.
The wild yak was once numerous and widespread on the entire Tibetan plateau north of the Himalayas. Currently it is found in remote areas of the Tibetan plateau and adjacent highlands, including Gansu Province, China, with a few having been observed in the Chang Chenmo Valley of Ladakh (eastern Kashmir, India). Wild yak distribution is highly clumped, with most animals in widely scattered herds, concentrated in the areas with little disturbance by humans. A survey conducted in 2003 found increasing populations of wild yak compared to previous surveys taken 10 years earlier.
Uncontrolled hunting by natives and military personnel is the main reason for the wild yak's decline. Its range has been reduced by more than half during this century. Poaching remains the main current threat. The wild yak has lost most of the best alpine meadow and steppe habitat to pastoralists. Problems are also caused by habitat disturbance, hybridization and competition with domestic yaks, and disease transmitted by domestic yaks.
The yak was probably domesticated in Tibet during the first millennium B.C., and domesticated animals now occur throughout the high plateaus and mountains of Central Asia, in association with people. Yaks found in zoos are usually of the domesticated variety, which is smaller than the wild yak. There are now more than 12 million domestic yaks in the highlands of Central Asia.
The wild yak is supremely well adapted to the harsh highlands with its thick coat, great lung capacity, and ability to clamber nimbly over rough terrain. Even its blood cells are designed for high elevations - they are about half the size of those of cattle and are at least three times more numerous, thus increasing its blood’s capacity to carry oxygen. Its thick coat and low number of sweat glands are also efficient adaptations for conserving heat. (Schaller 1998)
*** In winter the yak survives temperatures as low as - 40 deg C (- 40 deg F).
*** Wild yak herds travel on snow in single file, carefully stepping on footprints left by the lead yak.
Status and Trends
1960's - 1994: Endangered
2000 - 2004: Vulnerable (Criteria: A1cd+2cd, C1) (Population Trend: Decreasing) (IUCN 2004)
Countries Where the Wild Yak Is Currently Found:
2004: Occurs in China and India. May be extinct in Nepal. (IUCN 2004)
[Note: Figures given are for wild populations only.]
1995: A preliminary estimate of around 15,000 (Schaller 1998)
2003: Likely to be less than 10,000 mature individuals (IUCN 2004)
History of Distribution:
The wild yak was once numerous and widespread on the entire Tibetan plateau north of the Himalayas, in central China, India (Ladakh), Bhutan and Nepal. By around 1970 it was thought to occur only in remote areas, mainly in the northern and especially the northeastern parts of Tibet above 4000 m (13,000'), with a few animals still existing in Sikkim.
Currently it is found in remote areas of the Tibetan plateau and adjacent highlands, including Gansu Province, China, with a few having been observed in the Chang Chenmo Valley of Ladakh (eastern Kashmir, India). Wild yak distribution is highly clumped, with most animals in widely scattered herds, concentrated in the areas with little disturbance by humans.
For the most part, the wild yak's eastern limit now lies at the transition zone between alpine meadow in the east and alpine steppe in the west. From here its range extends westward through southwestern Qinghai Province, China. The western limit of the wild yak's distribution lies between the Karakoram and Kunlun Ranges in an area known as the Aksai Chin. (Oakland Zoo, Schaller 1998) A recent survey conducted on the Tibetan plateau by American and Chinese scientists found increasing populations of wild yak compared to previous surveys taken 10 years earlier. Tibet's Forestry Department has apparently made wildlife protection a priority, with the result that populations of rare animals are rebounding. (Schaller 2003)
Distribution Map (4 Kb GIF) (Huffman 2004)
Threats and Reasons for Decline:
Uncontrolled hunting is the main reason for the wild yak's decline, and it is still the most serious current threat. Its range has been reduced by more than half during this century. In addition, the wild yak has lost most of the best alpine meadow and steppe habitat to pastoralists. Problems are also caused by hybridization and competition with domestic yaks, as well as by disease transmitted by domestic yaks.
Data on Biology and Ecology
Size and Weight:
The male wild yak can weigh up to 1000 kg (2200 lb); females are 1/3 that size. Its shoulder height can reach over 2 m (6.5').
The wild yak occurs (or has occurred) in treeless uplands, including plains, hills, and mountains, from as low as 3200 m (10,500') up to the limit of vegetation at about 5400 m (18,000'). It reached its greatest abundance on alpine meadows. On alpine steppe, herds were also large on occasion but were more widely dispersed, and in desert steppe they were scarce. (Schaller 1998)
The wild yak is one of the species that live in both the Mountains of Southwest China Biodiversity Hotspot (Cons. Intl. 2005) and the Tibetan Plateau Steppe Global 200 Ecoregion. (Olson & Dinerstein 1998, Olson & Dinerstein 1999)
Age to Maturity:
In domestic yaks, females first conceive at the age of 3 - 4 years. Full size is reached at 6 - 8 years.
Approximately 260 days (Bhatnagar 2002).
Most births would be expected to occur from April through June (Schaller 1998). Mating occurs in September (Bhatnagar 2002).
Domestic yaks give birth to single calves in alternate years, but in areas of poor grazing, a few may give birth only once every three years, according to local informants. Wild yaks probably have a similar calving interval. (Schaller 1998)
Weaning takes place about 1 year after birth (Bhatnagar 2002).
Young become independent after about 1 year.
23 years (Bhatnagar 2002).
The wild yak grazes on grasses, herbs, mosses, and lichens, and crunches ice or snow as a source of water (Burnie & Wilson 2001).
The wild yak feeds mostly in the morning and evening. Due to the sparseness of vegetation in its environment, the yak must travel long distances to obtain its needed nourishment. It is a sure-footed climber. The wild yak is extremely sensitive to heat and coordinates its seasonal movements with the temperature and food supply. While in the highlands, the wild yak withstands violent winds and snowstorms for hours at a time. It can tolerate temperatures of -40° C (-40° F [Ed. note: Yes, the Fahrenheit and Centigrade temperature scales are the same at -40°!]). It also bathes in lakes and streams in severe cold. The wild yak stays in high areas with permanent snow during the relatively warm months of August and September and spends the rest of the year at lower elevations.
The wild yak is generally wary - if a herd is disturbed, the yaks will flee for a long distance, galloping with their tails held erect (Bhatnagar 2002).
Most wild yak cows are in large herds with their young with up to 100 or more animals of all ages and usually both sexes. Herds are not stable units: they readily split, or two or more may join. In the Aru Basin, mean herd size (n = 64 herds, excluding solitary individuals) is 24.5 and the median is 58.1; elsewhere in the Chang Tang reserve, mean herd size (n = 109 herds) is 11.3 and the median is 26.5. (Schaller 1998)
The wild yak is highly gregarious. Females and young congregate in large herds, which formerly were reported sometimes to contain thousands of individuals, while adult males spend most of the year alone or in groups of as many as 12. (Tan 1996)
Density and Range:
About 12% of the Chang Tang reserve in Tibet, China is composed of areas of moderate-to-high wild yak density of about 13 sq km/yak (5.0 sq mi/yak). Low-density areas in the reserve may average about 30 sq km/yak (12 sq mi/yak) with an estimated 100 sq km/yak (39 sq mi/yak) in very low density areas. Based on rough calculations, the reserve had a density of about 42 sq km/yak (16 sq mi/yak). (Schaller 1998)