Chimpanzees are Wired for Long-Term Memory to Hunt for Food

Chimpanzees have to scavenge for food daily, and a part of that is remembering which trees have fruit and which don't. But what do chimps do when all of the fruits are gone from their favorite food tree? Scientists have discovered that chimpanzees use long-term memory to remember the size and location of fruit trees and feeding experiences from previous seasons using a memory window which can be two months to three years ago.

In order to examine how chimpanzees remember which trees are best to harvest for food, the researchers examined chimps in the Tai National Park in Cote d'Ivoire. In all, they recorded the behavior of five chimp females for continuous periods of four to eight weeks, totaling 275 complete days, throughout multiple fruiting seasons.

During the course of their observations, the scientists found that chimpanzees fed on significantly larger trees than other reproductively mature trees of the same species, especially if their fruits emitted an obvious smell. Trees that were merely checked for edible fruit were also larger, despite not having smells. In fact, researchers discovered that 13 percent of trees were approached in a goal-directed manner while the chimps were traveling.

These targeted approaches in particular interested the researchers. They were unlikely initiated by visual cues, which suggests that this monitoring was guided by a long-term "what-where" memory of the location of large potential food trees. This, in turn, suggests that these chimps are capable of such long-term memory.

"The present study on chimpanzees is the first to show that our close relatives use long-term memory during their search for newly produced tropical fruit, and remember feeding experiences long after trees have been emptied," said Karline Janmaat, one of the researchers, in a news release.

In fact, the researchers found that one female that was followed over three consecutive summers could remember feeding experiences across fruiting seasons. In addition, long-term phonological data on individual trees showed that the interval between successive fruiting seasons, and thus the "memory window" of chimpanzees, could vary from two months to three years.

"For a long time people claimed that animals, contrary to humans, cannot remember the past," said Christophe Boesch, one of the researchers, in a news release. "This study helps us to understand why chimpanzees and other primates should remember events over long periods in time. And guess what? It also shows they do!"

The findings are published in the journal Animal Behavior.