Two’s company, six is a crowd??


MSc student, Sophie Kirklin, had a very eventful orangutan follow recently. Six wild orangutans, one close encounter, one tree pushed over, one uncooperative mating and one distressed infant, and all before lunch!

The morning started as usual; up at 3:40am to reach the orangutan’s night nest before it was abandoned.  The walk was quick as Aman (OuTrop field assistant) and I rushed through the forest to get to the nest.  After arriving, we soon realised that our focals, Teresia and her son Trevor, were no longer in their nest. We split up to search and it didn’t take us long to find the pair.

Suddenly, we heard trees rustling all around us.  Two more orangutans were approaching from opposite directions.  We identified a small juvenile female as Timi, the independent daughter of Teresia.  The other was a flanged male, who we did not recognise. This was my first sighting of a flanged male and, as if he knew, he headed straight toward me to take a closer look.
Unknown adult flanged male in the Sabangau Forest. Photo by Andrew Walmsley/OuTrop.
He stopped directly above where I was sitting and began growling deeply. I dropped to the ground and pretended to eat leaves, acting as submissive as possible. He soon lost interest and carried on swinging through the trees; turning his attention to Teresia.
Soon after this, another group of researchers from the OuTrop team, showed up, right behind a second flanged male. With two large males in the same area, they both attempted to display their great strength. The newest arrival began to shake a huge tree and we all rushed back, just before it came crashing to the ground! 
Male orangutan showing he means business! Photo by David Ehlers Smith/OuTrop.
After the males moved on, we heard long calls from both males, which continued for a few hours. Orangutan long calls can travel up to 1km through the forest, but these were coming from 100 metres away, and at times as close as 20 metres! The males use long calls to advertise their presence to females, and to other males who may also be in the area.  An ‘impressive’ long call can deter a rival male from competing for a female with the caller. 
Just after these calls ended, a small unflanged male appeared. He headed straight for Timi, who was feeding in a nearby tree.  She is a juvenille, but may be old enough to be sexually mature, and so he mated with her, although she protested.  I have read that unflanged males are sneaky, as they are relatively unappealing to females, so they will often force uncooperative mating.

The male then clambered towards Teresia.  When he got close, her small son Trevor began to cry.  The male investigated Teresia, but given the young age of Trevor, Teresia is unable to conceive at this time. As soon as he moved away, Trevor stopped crying and Teresia resumed her normal activities.
Following a very eventful start to the day, we continued recording data never knowing what was around the next tree!
Teresia and Trevor. Photo by Emily Boucker/OuTrop.