Experimental evidence for route integration and strategic planning in wild capuchin monkeys

Abstract

Both in captivity and the wild, primates are found to travel mostly to the nearest available resource, but they may skip over the closest resource and travel to more distant resources, which are often found to be more productive. This study examines the tradeoff between distance and reward in the foraging choices of one group of wild capuchin monkeys (Cebus apella nigritus) using feeding platforms in large-scale foraging experiments conducted over four years. Three feeding sites were arrayed in an oblique triangle, such that once the monkey group had chosen one site to feed, they had a choice between two remaining sites, a close one with less food and the other up to 2.3 times as far away but with more food. Sites were provisioned once per day. The capuchins generally chose the closer feeding site, even when the more distant site offered up to 12 times as much food. The distances to, rewards of, or various profitability measures applied to each alternative site individually did not explain the group's choices in ways consistent with foraging theory or principles of operant psychology. The group's site choices were predicted only by comparing efficiency measures of entire foraging pathways: (1) direct travel to the more rewarding distant site, versus (2) the longer 'detour' through the closer site on the way to the more distant one. The group chose the detour more often when the reward was larger and the added detour distance shorter. They appeared to be more sensitive to the absolute increase in detour distance than to the relative increase compared to the straight route. The qualitative and quantitative results agree with a simple rule: do not use the detour unless the energy gain from extra food outweighs the energy cost of extra travel. These results suggest that members of this group integrate information on spatial location, reward, and perhaps potential food competition in their choice of multi-site foraging routes, with important implications for social foraging.

A socioecological perspective on primate cognition, past and present

“…In an experimental Weld study, Janson (1998) found that capuchins were willing to travel further for more productive sites. 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.…”

“…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.…”

“…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).…”

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

“…For this reason, most observational and experimental Weld studies of spatial memory (e.g. Boesch and Boesch 1984;Garber 1988Garber , 1989Garber and Dolins 1996;Garber and Hannon 1993;Garber and Paciulli 1997;Janson 1996Janson , 1998Janson , 2007Menzel 1991;Noser and Byrne 2007;Pochron 2001;Robinson 1986;Sigg and Stolba 1981;Valero and Byrne 2007) and experimental captive studies (e.g. Gallistel and Cramer 1996;MacDonald and Wilkie 1990;Menzel 1973;Menzel 1999;Tinklepaugh 1932) have focused on primates which, in nature, inhabit large home ranges with widely dispersed resources.…”

“…It is less obvious whether in situations of high food-patch density, reliance on spatial memory is necessary (Janson 1996). Even when food patches are common, primates might rely on spatial memory to travel to highly productive or preferred resources, rejecting less productive but closer resources (Garber 1989;Janson 1998Janson , 2007. Conversely, certain trees might be avoided because they are distasteful (e.g.…”