Like in all orangutan populations, adult females at Suaq have a more or less fixed home range in which they spend most of their time. Those home ranges are heavily overlapping with the home ranges of multiple other females. Daughters usually settle in an area close to their mother’s home range. Males, on the contrary, leave their natal area when they grow up.

Xenix, a big unflanged male. Photo credit: Caroline Schuppli, 2010.

Flanged and unflanged males

When reaching adulthood, young males fist go through an unflanged stadium where they are only marginally bigger than females. At Suaq, this stadium can last anything from a couple of years to multiple decades. However, most likely dependent on the presence or absence of flanged males in the area, or the physical condition of those, unflanged males eventually go through a secondary growth spurt during which they grow cheek pouches as well as a throat sack and gain a lot of weight.

Pluto, a subordinate flanged male at the Suaq research area. Photo credit: Christiaan Conradie, April 2014.

At Suaq there is always one dominant flanged male in the area

The resident flanged male defends his territory against other males with long distance calls, so called long calls. Long calls can be heard through the forest over a distance of up to 1 km. Females actively seek the protection of their local dominant flanged male. When they get into their receptive phase, females voluntarily copulate with the local flanged male. He will be the father of the majority of their offspring.

Ellie and Rakus, hanging out together. Photo credit: Caroline Schuppli, December 2010.

Friendships between males and females?

Whereas at other sites females almost only associate with their female relatives, at Suaq they also tolerate unrelated unflanged and flanged males very close by. Regularly we find them to spend multiple days in a row in close and peaceful association without copulation attempts. With our research, we want to find out more about the association patterns of and social interactions between males and females.