Written by Ika (BNF Primate Scientist) and Supian (BNF Red Langur Project Coordinator)
Communication has a very important role in the social life of primates, such as individual identification; sharing information on predators and food availability; and facilitating social interaction within a group and with other groups closeby.
This includes the two red langur groups we study in the Sabangau Forest. BD Group and Mafia Group are the two most habituated red langur groups in Sabangau, and they have very unique habits related to their loud call.
Male red langurs give a loud call every morning that serves as a wake up call; the purpose is to tell the other members of the group to wake up and start their activities, like feeding.
Some anthropogenic factors around the forest can also trigger a loud call from the male in the group. Sabangau Forest’s close proximity to the airport in Palangka Raya (± 30 min car ride), makes it possible for us to hear the sound of the airplane engines when they fly above the forest.
When the planes fly above the red langurs’ home range, the male of BD Group will run away to avoid the grumbling sound of the engine, making a loud call, and when the plane has disappeared into the distance he will resume his activities.
A few years ago, there was a helicopter which carried water from the Sabangau River to extinguish a forest fire near Sabangau. The male of BD gave a loud call whenever he heard the sound of the helicopter’s propeller. The females and juveniles of the group also sometimes vocalise to respond to the male’s loud call.
Things are slightly different with the Mafia Group. We’ve been observing them for some time now and we found that the male of the group always gets ‘excited’ whenever there is heavy rain. The male will run around the area while making a loud call, more like a celebration, while the females will try to find shelter.
We’re still investigating the causes of the loud calls from BD’s male. It could be just a mere response to disturbance, or perhaps he thought that the sounds were from predators and they felt threatened. We are also curious as to what causes the male from Mafia to get ‘excited’ with the presence of heavy rain. Who’s interested to find out more? Stay tuned as we share more of our discoveries from the forests of Borneo.
You can hear a red langur loud call here!