Yak (Bos mutus)

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

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.13Males 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.12Studies 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