Species accounts

Bos grunniens TAXONOMY

Bos grunniens Linnaeus, 1766, boreal Asia.

OTHER COMMON NAMES French: Yack.

PHYSICAL CHARACTERISTICS

Body length 94.4-127.9 in (240-325 cm); shoulder height 62.9-80.7 in (160-205 cm); tail length 23.6 in (60 cm); weight males 1,100-2,645 lb (500-1,200 kg), females 660-770 lb (300-350 kg). Moderate sexual dimorphism, with females weighing only about 33% of adult males; stocky, ox-like animals with a broad, low-hung head raising steeply to humped shoulders, which are followed by a lower back and rump. Both sexes have long, simple curved, black horns. In adult males, the horns extend up to 37.4 in (95 cm), whereas those of females normally only attain 19.6 in (50 cm). The pelage of wild yak is black with rusty-brown tints and, sometimes, gray hairs on the muzzle. The domesticated yak varies greatly in color from black to light yellow-brown, with many individuals having mottled white patches over parts of their sides and backs. The guard hair is relatively short on the back; on the sides, it can be up to 27.5 in (70 cm) in length, hanging down to form a fringed cape, which extends far enough to the ground to have the legs appear deceptively short. Their long tail is exceptionally bushy throughout.

DISTRIBUTION

The wild yak occurs on the Tibetan Plateau in northern Xizang Province (Tibet) and western Qinghai Province of China. Its historic range included mountains and plateaus of western China, northern India, Nepal, and parts of Mongolia.

Domesticated yak are distributed more broadly across the highlands of central Asia.

HABITAT

A species of the high altitudes, it is found on high elevation alpine steppes devoid of trees and bushes, down to elevations of 6,560-16,400 ft (2,000-5,000 m). In late summer, yaks exploit this alpine-tundra biome foraging on the pockets of natural pasture. As snow begins to accumulate during fall in these high elevations, they migrate to windswept areas of shallow snow or to lower elevations where there are greater amounts of accessible vegetation, such as in valleys and on plateaus.

BEHAVIOR

Yaks form herds, but they are segregated by sex. Female herds comprised of adult females, their calves, and juvenile females and males are typically 6-20 animals, but occasionally more than 100. When males become sexually mature, they leave these female groups and join with older bulls to form all-male herds that are generally 2-5 animals, with some as large as 19. Older bulls are often solitary. When threatened, group members either flee or bunch together and collectively face the predator. In either case, if young are present, they tend to be in the center of the group. During the rut in September, mature bulls join female groups during the four-week breeding season. Males compete for females, and rival males fight by trying to gore each other's flanks.

FEEDING ECOLOGY AND DIET

During summer, yaks consume a variety of growing grasses and forbs such as wildflowers, and supplement their diet with shrubs and lichen. During winter, they consume the dormant grasses and lichens, including some mosses. Yak make altitudi-nal migrations to exploit seasonal availability of forage.

REPRODUCTIVE BIOLOGY

Polygynous. Reproduction is timed to benefit from the relatively short season of plant growth and less inclement weather; they mate in September, and after a nine-month gestation period, the single calf is born in June. Females give birth every second year.

CONSERVATION STATUS

Classified as Vulnerable, wild yaks face habitat loss and degradation due to livestock grazing on their natural pastures. These alpine/tundra steppes are low in plant productivity and so competition with livestock is exacerbated. Hunting by local people for meat and hides continue to contribute to extirpation of wild yaks. Besides ecological factors, interbreeding between domestic yak and wild yak may pose additional threats to wild populations.

SIGNIFICANCE TO HUMANS

First domesticated over 4,000 years ago, they have supported human life throughout this time in harsh high elevation environments. They are still important to the society and economies of local peoples in many mountain areas in central Asia. Wild yaks are hunted in some areas for meat, wool, and other products. Domestic herds provide milk, cheese, meat, wool, and hides, as well as draft animals and for transporting goods. Their dung is collected for fuel. ♦

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