About male orangutans

In an orangutan context, "dominance" refers to the social hierarchy or status of an individual within a population.

Dominant male orangutans produce higher amounts of testosterone compared to their submissive counterparts, which determines the likelihood of flanges appearing. Although unflanged males can still engage in mating and father offspring, their testosterone levels are lower than those of dominant males.

Flanges are distinct facial features that develop on the sides of male orangutan faces, extending from their cheekbones to their temples. They demonstrate maturity and can develop during puberty. Flanges serve multiple purposes, such as amplifying vocalizations, displaying dominance to other males, and attracting females during mating season. The size and shape of flanges can vary among different orangutan species and individuals.

The average time for flanges to develop is one - two years. Here is a photographic timeline of Malim, a wild, dominant male who visits Sepilok regularly.