After tracking the chimpanzees over the span of 4 to 8 weeks, the scientists made another discovery: travelling chimps would swerve toward their favorite trees long before they could have sensed the fruit. (The siren smells or sights of the five-star fruiting trees, in other words, weren't attracting the chimps.) It was the memory of the good food, the scientists believe, that lead these chimps back to their favorite trees.
This indicates "a daily use of an exceptionally long-term prospective memory," the study authors write. Although researchers have noted that rats and pigeons can remember tasks, these are in the shorter term -- ranging from 10 seconds to 15 minutes. When the chimps acted on their memories, it was an average 80 minute-long walk away from their favorite trees. Good fruit, it seems, makes a lasting impression on chimpanzees.