Today we are in Sarawak in Borneo and finally found a mature male orangutan. WOW! It was easy to notice they have strange flappy face-pads called flanges, which females find attractive – yet males may wait 20 years before developing them.

Mature male orangutans have large flappy cheek-pads, known as flanges. As far as females are concerned, they prefer males with them, over those without. Fully mature males are also twice the size of females and grow large throat sacs, all of which are characteristics associated with dominance. The long vocalizations of the flanged males also set them apart from an unflanged male Bornean orangutan. The long vocalizations help males to attract females.

But these traits can take a while to show. Some wild male orangutans take 20 years to grow flanges. Fully mature males are also twice the size of females and grow large throat sacs, all of which are characteristics associated with dominance.

A new study tries to explain why males take so long to grow their flanges. To discover this, researchers collected poo from 17 wild Bornean orangutans. The researchers then analyzed the hormone levels in the orangutans’ poo.

As soon as males begin to develop bigger cheek pads, their testosterone levels peak. “The very high testosterone levels of the one developing male in the study was a bit surprising but indicates the need for high testosterone levels to develop secondary sexual characteristics [such as cheek-pads]”. When a male becomes “fully-flanged”, his testosterone levels out again. As well as an advantage when it comes to finding mates, studies show that those with larger cheek pads are also healthier. Weaker and older males have shrunken flanges.

Check out the the collage at the end of the post.