Anthropologists at the University of Zurich say both captive and wild-living orangutans, to attract females and repel male rivals, call in the direction in which they are going to be traveling.
Many scientists have long thought only humans had the ability to anticipate future actions, whereas animals were believed to be trapped in the here and now, but experiments with great apes in zoos have shown they remember past events and can plan for their future actions.
The Swiss researchers, following wild orangutans for several years through the dense tropical swamplands of Sumatra, have found they also display planning skills. While orangutans generally journey through the forest alone, they also maintain social relationships, and adult males will emit loud, long calls to attract females and repel rivals.
Using their cheek pads as a funnel for amplifying the sound in the same way as a megaphone, wild orangutans were observed directing the calls in particular directions and then moving off on that heading, the Swiss researchers said.
"To optimize the effect of these calls, it thus would make sense for the male to call in the direction of his future whereabouts, if he already knew about them," Carel van Schaik said. "We then actually observed that the males traveled for several hours in approximately the same direction as they had called."
The direction of calls made around nesting time in the evening predicted the travel direction of the next day, van Schaik said, suggesting orangutans plan their route up to a day ahead.
"Our study makes it clear that wild orangutans do not simply live in the here and now, but can imagine a future and even announce their plans," he said. "In this sense, then, they have become a bit more like us."