When growing up, male orangutans will leave their natal home range and move into a new area. There they will first go through a so-called unflanged stadium. This phase can last anything from a couple of years to several decades. For most of the time, unflanged males are only marginally bigger than females. Only when they are about to go through their secondary growth spurt and develop flanges they will slowly get bigger and bulkier.
At Suaq there is an exceptionally large number of unflanged males: unlike in other populations, there are much more unflanged males than flanged males. The Suaq unflanged males are also uniquely sociable and like to hang out together. We mostly find them in small groups of 2-5 males, whereby the compositions of these groups change constantly.
The Suaq unflanged males also like to hang out with females and adolescents. Since the unflanged males originally come from other areas we suspect that by spending time with resident orangutans, they will learn about the local diet and traditions.
However, unflanged males are also known to sneak copulate with the local females, which is most of the time against the females will. The unflanged males have to make sure that they are not caught by the locally dominant flanged male who will defend his females.