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Captive yak, Tianzhu, Gansu, China (Jianlin Han)

Yak (Bos mutus)

Physical characteristics

There is a high degree of sexual dimorphism between males and females. Body mass of a wild male yak is estimated to be between 800–1200kg.5,9,11,12 Females weigh around 350kg.13 Males stand at 175–203cm shoulder height and females 137–156cm.13 The yak’s horns vary a lot in size and shape, with the males having far larger horns than the females. Generally have a wide lateral sweep, turning forward and finally upward and slightly bent inward. Smooth except for a few ridges at the base.12,14 Adult yak generally have black pelage with rust-brown hues and sometimes a sprinkling of gray on the head and neck.12 Yak are adapted for life in extremely low temperatures, high elevation, extreme solar radiation, relatively arid conditions, and low oxygen.12

Life history 

  • Longevity: Captive individuals live for around 20 years, and this is probably comparable to in the wild.12 Studies of reliably aged wild yaks found that the oldest died at 16 years old.11
  • Sexual maturity and gestation: Females breed for the first time between the ages of 3 and 4, and gestation lasts 258–270 days.12 Peak productivity of females occurs at 5–6 years old and declines after 9 years.9,12