If you're ever lost in the jungle, follow a chimpanzee. New research suggests the great apes keep a geometric mental map of their home range, moving from point to point in nearly straight lines.

"The kind of striking thing when you are with the chimpanzees in the forest is that we use a compass or GPS, but obviously these guys know where they are going," says Christophe Boesch, a primatologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig.

With the aid of GPS, he and colleague Emmanuelle Normand shadowed the movements of 15 chimpanzees in Côte d'Ivoire's Taï National Park for a total of 217 days.

In a given day, a single animal might visit 15 of the roughly 12,000 trees in its 17-square-kilometre range, Boesch says. "They are kind of nomads."

Chimp tracking

Each morning, researchers woke before a chimpanzee, and then tailed the animal until it went to sleep at day's end – often in a different nest. Researchers recorded their GPS position once a minute.

"We were able to do this study now because of the new GPS technology that works perfectly in the tropical forest. That was not the case five years ago," Boesch says.

After analysing all this data, he and Normand found good evidence that the animals chose their routes using a mental map built around geometric coordinates, as opposed to a navigation style based on landmarks for well-travelled routes.

While darting from fruit tree to fruit tree, individuals tended to move in straight lines, slowing only once they neared their destination. Chimps also visited trees from an angle that depended on current location.

This suggests the chimpanzees do not rely exclusively on landmarks such as specific trees and streams to navigate. These markers could come in handy once a chimp nears its destination.

Travelling in styles

Previous research and everyday experience suggests that humans, too, employ both styles of navigation, depending on their environment.

"In a city you can use roads, which are the classical landmarks, whereas if you are a Pygmy in the tropical rainforest or an Eskimo in the Arctic, where you have nothing as a landmark, then you will learn to get by using more sophisticated means," Boesch says.

Paul Garber, a biological anthropologist at the University of Illinois in Urbana-Champaign, thinks that point-to-point distance might not be the only factor involved in a chimpanzee's choice of route.

Quantity and quality of food, as well as competition, could play a role in route choice. Also, like travelling salesmen who optimize their travels, chimpanzees may be thinking about navigation with an eye to the future, Garber says. "They may be planning not just one step in a route, but many, many steps ahead."

Journal reference: Animal Behaviour (DOI: 10.1016/j.anbehav.2009.01.025)

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