Effect of Fruit Scarcity on Use of Spatial Memory in a Seed Predator, White-faced Saki (Pithecia pithecia)

Many studies have shown that primates use spatial memory to travel efficiently between important resources such as trees with ripe fruit or water holes. White-faced sakis (Pithecia pithecia) have shown strong evidence of spatial memory as they travel efficiently to feed on the seeds of highly productive fruit trees and the ripe fruit of a highly preferred tree species and to drink from natural cisterns in trees. Researchers theorize that primates rely less on memory when they feed on more evenly dispersed food. Here we examine the use of spatial memory in a group of wild white-faced sakis during a month of fruit scarcity when they foraged for desiccated seeds, leaves, insect material, and flowers. We used logistic regression and three computer models (the geometric model, the step model, and the change point model) to analyze their movement patterns. We find that the focal group does not demonstrate the use of memory. These results are in contrast to results from a study of spatial memory with the same focal group in the two immediately preceding months. The results conform to theories on the role of nutritionally dense and patchy foods in driving the use of memory during travel between feeding sites. They demonstrate that, within a short time, a group of primates can vary from a strong reliance on spatial memory to no demonstrable use of spatial memory.