Male orangutans announce their travel plans to others up to one day before embarking, scientists have found after observing the animals in the wild.
The capacity for long-term planning, which involves higher order cognitive abilities like self-control, was once thought to be a uniquely human trait. Recent experiments have shown that, like humans, some great apes and other species are able to plan for the future, however. In one case from 2009, a chimpanzee in a zoo in Sweden collected and stored stones and pieces of concrete, later using them as ammunition on park visitors. The current research, published in PLoS One, provides more evidence that great apes like orangutans have skills needed for long-term planning, and describes a situation in which the ability to plan is adaptively beneficial.
Anthropologists from the University of Zurich observed and recorded the travel habits of Sumatran orangutans in Suaq Balimbing, a tropical forest in Indonesia. Orangutans live a nomadic, semi-solitary lifestyle. A single male will typically control an area that is also home to a handful of females, who either live alone or with their offspring. Dominant males grow wide flaps around their faces, called flanges, and emit loud, “long calls” about four times a day. Flanges may help to amplify the males’ calls, which are audible for over one kilometer and serve to alert other orangutans in the area to their movements.
Using a sample of 1169 calls emitted by 15 males over 320 days, the researchers examined whether long calls predicted an orangutan’s future movements, indicating an ability to plan ahead. To make that determination, the researchers measured the angle between the direction of an orangutan’s call and the direction of its journey. They found that the direction of an orangutan’s long call predicted its movement up to 22 hours later, even after breaks for eating and sleeping. Furthermore, when a dominant orangutan would change direction, he would often emit another long call, which predicted his new path better than the original.
The researchers also recorded the movements of the orangutans in the vicinity of the dominant male. When the call was faint, they noticed that females would move in the same direction to catch up with the dominant male. Subordinate males, on the other hand, would move in the opposite direction of the call to get out of the dominant male’s way.
Since solitary orangutans must maintain contact with others while ranging through large tracts of forest in search of food, it makes evolutionary sense that they would have the ability to plan and communicate their future movements, the researchers said.