Integrating information about location and value of resources by white-faced saki monkeys (Pithecia pithecia)

Abstract

Most studies of spatial memory in primates focus on species that inhabit large home ranges and have dispersed, patchy resources. Researchers assume that primates use memory to minimize distances traveled between resources. We investigated the use of spatial memory in a group of six white-faced sakis (Pithecia pithecia) on 12.8-ha Round Island, Guri Lake, Venezuela during a period of fruit abundance. The sakis' movements were analyzed with logistic regressions, a predictive computer model and a computer model that simulates movements. We considered all the resources available to the sakis and compared observed distances to predicted distances from a computer model for foragers who know nothing about the location of resources. Surprisingly, the observed distances were four times greater than the predicted distances, suggesting that the sakis passed by a majority of the available fruit trees without feeding. The odds of visiting a food tree, however, were signiWcantly increased if the tree had been visited in the previous 3 days and had more than 100 fruit. The sakis' preferred resources were highly productive fruit trees, Capparis trees, and trees with water holes. They traveled eYciently to these sites. The sakis choice of feeding sites indicate that they combined knowledge acquired by repeatedly traveling through their home range with 'what' and 'where' information gained from individual visits to resources. Although the sakis' foraging choices increased the distance they traveled overall, choosing more valued sites allowed the group to minimize intragroup feeding competition, maintain intergroup dominance over important resources, and monitor the state of resources throughout their home range. The sakis' foraging decisions appear to have used spatial memory, elements of episodic-like memory and social and nutritional considerations.

A socioecological perspective on primate cognition, past and present

“…Janson (2007) presents experimental data that shows that capuchins will skip a smaller resource if visiting the smaller site adds too much travel time to reaching a larger site. Cunningham and Janson (2007) present observational data indicating that the travel path of saki monkeys is determined by highly productive trees.…”

“…Episodic memory binds together where, what, and when information in a recollection of a personal event [see Clayton et al (2001) and Cunningham and Janson (2007) for a discussion of episodic memory]. So far, the ability to integrate all three aspects of episodic memory has been convincingly demonstrated only in food-caching jays (Clayton et al 2001(Clayton et al , 2003.…”

“…Valero and Byrne (2007), Cunningham and Janson (2007) and Janson (2007) look at the information that monkeys integrate when deciding on a foraging path. Valero and Byrne's analysis of the foraging routes of their study subjects, suggest that the spider monkeys plan their routes more than one step at a time.…”

“…There is abundant evidence that local availability of food may aVect social decisions, including the tendency to form subgroups ), number of animals in a feeding tree (Leighton and Leighton 1982), and levels of aggression (Cunningham and Janson 2007;McFarland Symington 1988). However, there is little evidence that actual foraging decisions diVer under distinct social circumstances.…”

“…Menzel's (1971) remarkable experiments indicated that, without any overt calls or gestures, chimpanzees were able to communicate to each other about the presence and quantity of hidden food. In nature, primate groups sometimes travel to more distant, more productive resources, instead of nearer, less productive ones (Cunningham 2003;Cunningham and Janson 2007;Garber 1989;Janson 1996Janson , 2007. Traveling to more productive trees can reduce competition within the group and facilitate group cohesion (Garber 1988;Janson 1988;White and Wrangham 1988;Whitten 1988).…”