Sumatran orangutans plan their trips through the Indonesian jungle in advance, according to a new paper published in PLOS ONE. The new research upends yet again the belief that humans are unique in the animal kingdom, suggesting that orangutans, like humans, can plan for the future, at least to some degree.
“There are many scientists (mainly working on human cognition) assuming that only humans are capable of thinking about the future,” said Karin Isler, a researcher at the Anthropological Institute and Museum in Zurich, Switzerland and a co-author on the paper, said in an email interview.
But, according to this latest research, that isn’t the case, with orangutans joining us in planning their routes with forward-thinking aplomb – and without the gentle guidance of Apple’s Siri.
Orangutans, the red-haired, big-bellied primates, have often roiled prevailing theories of what makes a human a human, flagrantly displaying abilities that remind us of, well, us.
In a 2003 paper, published in Science, researchers reported that orangutans exhibited what could be construed as “culture,” proposing that separate groups of animals’ unique rituals were not just adaptive strategies suited to their different environments, but were cultural practices. Then, a 2006 paper, also published in Science, found that captive orangutans and chimpanzees can choose and store tools and then remember to use them 14 hours later.
But whether or not orangutans can plan their routes in advance has been unclear. The distinction between orangutans truly planning ahead, as opposed to just acting on their immediate needs, is difficult to tease out.
“Many animals know where they are heading, but it's difficult to say whether these plans are beyond their current motivation (e.g. being hungry or thirsty, and moving directly to a food or water source),” says Dr. Isler.
Over a period of five years, researchers from the Anthropological Institute and Museum at the University of Zurich collected 1,169 long calls from flanged male orangutans in Suaq Balimbing, a peat swamp forest in Gunung Leuser National Park in Indonesia. (“Flanged” means that the orangutans are sexually mature and can emit calls using their throat pads.)
About 696 of those calls, emitted on 320 days, came from a dominant male, the orangutan that commands female attention in his group, as opposed to the unfortunate, submissive males who do not win the hearts of girl orangutans.
The researchers found that flanged, dominant male orangutans emit long calls in the direction of their planned travel route, emitting a new call before each change in direction. The orangutan’s commitment to its called direction held true even after a night’s rest, proving that the calls did not represent immediate needs but long-term plans, the authors say. If an orangutan sounded a directional call at night and then went to sleep, it would resume travel in the direction indicated the night before upon waking the next morning. In fact, the orangutan would continue in that direction for 22 hours after the directional call was given.
“These findings therefore indicate that flanged male Sumatran orangutans make their travel plans at least a day in advance and announce them through their spontaneous long calls,” write the scientists, in the paper. “He remembers the main travel direction in the face of numerous distractions, sometimes lasting for hours, or even overnight.”
The paper authors also note that orangutan’s directional planning differs from that exhibited in migrating birds and homing pigeons, as the orangutan is capable of changing his route and destination throughout the trip.
These calls have an audience: female orangutans. The researchers propose that the females use the dominant male’s calls to tail their preferred mates and avoid the lower-status male orangutans pining for them. After hearing the call, females moved closer to the dominant, call-emitting males, remaining within earshot, the researchers found. The subordinate males, however, plodded away from the stronger male’s given destination.
The researchers do not identify the mechanisms responsible for the planning, noting that the position of the sun, a mental map, or some form of magnetic orientation abilities could be factors in the orangutan’s route mapping. And the results do not necessarily suggest that orangutans are like humans in setting distant goals and pondering the future.
“Planning travel routes does not directly allow for inferring other planning abilities,” says Isler.
The researchers expect that route planning abilities could be found in apes and other large-brained animals. Still, proving that to be true will be complicated, as other animals, unlike the orangutan, might not be so vocal about their plans, the authors write.