Humans pride ourselves on our ability to make plans for the future. But it turns out that we're not the only animals who think ahead. Scientists have observed wild orangutans planning their travel routes a day in advance, and communicating their itinerary to community members.
In the last decade, research has begun to show that some large-brained animals have the ability to plan for future needs — at least in captivity. The most famous example of this comes from Santino, the dominant male chimpanzee at Furuvik Zoo in Sweden. Zoo officials found that in the morning, before the zoo opened up, Santino would collect and cache stones from an adjacent waterbed. Later in the day, he would use those stashed stones as ammunition against zoo visitors. Last year, scientists also discovered that Santino hides his stone caches behind logs and rocks, and under small mounds of hay he creates.
In lab experiments, scientists have found that, when given a choice between tools, orangutans and chimpanzees chose the correct tool to get a reward an hour later. Other research has shown that captive orangutans and bonobos could choose, transport and save appropriate tools to use up to 14 hours later.
Some corvids are also known to think ahead. For example, in 2007, scientists found that western scrub-jays store food in places they know they'll have access to the next morning. And if they're given two types of food at night, they'll preferentially store the type of food they know they won't receive the next morning.
Despite the evidence that great apes and corvids (and potentially some rodents) can plan for the future in experimental tests, it's unclear if animals use this ability — which requires the synergy of self-control and mental time travel — in the wild. And if they do plan ahead in their natural setting, what shape does this preparation take?
To find out, anthropologists at the University of Zurich in Switzerland decided to take a look at flanged Sumatran orangutans (Pongo abelii) in a peat swamp forest in Indonesia. The primates are semi-sedentary and often out of sight of other orangutans in their population, but they do stay in vocal contact with one another.
Once they hit sexual maturity, males may grow flanges, which are wide pads on their cheeks made of cartilage. These flashy males will emit loud vocalizations, called "long calls," an average of four times a day. The long calls are audible for over 1 km (0.62 miles), lure in sexually active females and chase away lower-ranking males. But they also attract higher-ranking males.
"If he hears a call from a low-ranking male (they recognize the individual calls), he would probably approach and chase the 'intruder,'" study researcher Karin Isler told io9 in an email. "Unflanged males don't even call at all, to not attract attention."
The vocalizations are acoustically different depending on context. That is, males have different long calls for when they push over a dead tree, respond to another male's long call (or other stimulating event, such a tree falling) or just do spontaneously.
The spontaneous calls are particularly interesting because the males rigidly face a single direction while performing the vocalizations, which can last for up to four minutes. Additionally, their cheek flanges act as a kind of megaphone, amplifying the call in the forward direction — females in the wrong spot may hear only a faint call and have to move toward the male to remain in earshot.
Isler and her colleagues wondered if the flanged males are actually using the spontaneous long calls to broadcast the direction of their future travel — they roam around each day to find the semi-scarce fruits they survive on — to the females. They reasoned that the females could only stay in contact if they knew where the male was going.
Planning a Trip
The team analyzed nearly 1200 long calls of 15 flanged males, and looked at how the calls correlated with the movements of the males and other orangutans in the community. As expected, they found the direction of the males' spontaneous long calls during the day predicted the general path the orangutans were going to take for the next few hours (the orangutans had meandering routes with an overall direction because they can only travel along branches that hold their weight, rather than in a simple straight line). They gave a new call if they decided to change direction, though why they would alter their routes is unclear.
"Perhaps they hear other orangs that human observers don't hear," Isler said. "Or they just change their minds where to find food."
Sometimes the males would call out at night before going to bed — these vocalizations predicted their travel direction for up to 22 hours. The next day, females travelled in the same direction as the males without needing any reminders. Subordinate males, on the other hand, moved in opposite directions.
The study suggests flanged males plan their trips a day in advance, and communicate their itineraries to other orangutans, females especially. Males benefit from this practice by allowing sexually receptive females to reach them; females benefit by being able to stick close to the moving male and avoid being harassed — and forcefully mated — by subordinate males.
The researchers think the ability to plan for the future may be common in all wild great apes, and maybe even other wild animals. "Although difficult to demonstrate, it is likely that other large-brained animals, such as elephants or whales, also have a sense of past and future," Isler said.
Check out the full study over in the journal PLOS ONE.
Top image via puliarf/Flickr. Inset image via University of Zurich.