The southern white-cheeked gibbon[1] (Nomascus siki) is a species of gibbon endemic to Laos and Vietnam.
- It is closely related to the yellow-cheeked gibbon (Nomascus gabriellae) and Northern white-cheeked gibbon (Nomascus leucogenys).
- It has already been identified as a subspecies of each of them.
- Southern white-cheeked gibbons are sexually dichromatic, meaning the hairiness of each sex is quite different, clearly distinguishing females from males despite being roughly the same size.
- Females have golden and reddish fur, black faces, and black or dark brown hair on the crown. They have white fur around their face, which looks like a halo.
- Males have thick black fur and black facial skin with white cheek fur. They also have distinctive hair crests on the top of their heads.
- Babies are born with whitish-beige fur that turns black after the first two years of life. When they reach sexual maturity, the males remain black while the females turn into a golden whitish coat.
- Gibbons are very acrobatic primates and perfectly adapted to an arboreal lifestyle. They have long arms and fingers that allow them to propel themselves through the forest at speeds of up to 3 meters per stroke.
- In particular, their shoulder joints allow greater freedom of movement when swinging.
