In order to attract females and repel male rivals, orangutans call in the direction in which they are going to travel, researchers said.
Anthropologists at the University of Zurich have found that not only captive, but also wild-living orangutans make use of their planning ability.
For a long time it was thought that only humans had the ability to anticipate future actions, whereas animals are caught in the here and now.
Anthropologists have now investigated whether wild apes also have this skill, following them for several years through the dense tropical swamplands of Sumatra.
Orangutans generally journey through the forest alone, but they also maintain social relationships. Adult males sometimes emit loud 'long calls' to attract females and repel rivals. Their cheek pads act as a funnel for amplifying the sound in the same way as a megaphone.
Females that only hear a faint call come closer in order not to lose contact. Non-dominant males on the other hand hurry in the opposite direction if they hear the call coming loud and clear in their direction.
"We then actually observed that the males travelled for several hours in approximately the same direction as they had called," said van Schaik.
In extreme cases, long calls made around nesting time in the evening predicted the travel direction better than random until the evening of the next day.
Schaik and his team conclude that orangutans plan their route up to a day ahead.
In addition, the males often announced changes in travel direction with a new, better-fitting long call. Researchers also found that in the morning, the other orangutans reacted correctly to the long call of the previous evening, even if no new long call was emitted.
