Exploring New Areas: How Important is Long-Term Spatial Memory for Mangabey (Lophocebus albigena johnstonii) Foraging Efficiency?

Studies of primate foraging efficiency during the exploration of new areas can provide important insights into the adaptive value of long-term spatial memory. After 6 yr of observation of a group of gray-cheeked mangabeys (Lophocebus albigena johnstonii) in Kibale National Park, Uganda, we observed exploration of a new area, followed 7 mo later by a group split. We recorded their ranging and foraging behavior for 22 mo after the first exploration. Controlling for weather variables, we found that mangabeys moved longer daily travel distances, explored more area per day, and had larger group spreads in the new area compared to the old area in both parent and daughter groups. The increase in search swath in the new area likely enabled the monkeys to counteract their lack of knowledge of food locations in the new area, as the efficiency in finding fruit in general did not differ between the old and new areas. We did, however, find a lower efficiency in finding fruit from preferred fig trees whose edibility could not be assessed by visual cues in the new area. Fig finding efficiency remained lower, even when we controlled for potential differences in fig density. In addition, mangabeys traveled and foraged less often on the ground in the new compared to the old area. However, when the monkeys became more familiar with the new area, terrestrial behavior increased. Our results are consistent with the hypothesis that when monkeys move into an area in which they have no experience, an absence of knowledge acquired via long-term spatial memory decreases their foraging efficiency.