Abstract: In primate species with unidirectional dominance relationships, rank order restricts the access of nondominant females to clumped resources. However, females might attempt to bypass the rank order by reaching feeding sites before the highest ranking individuals (early arrival tactic) when there are net benefits. We therefore analyzed the order of arrival to the feeding site of the adult members of a captive group of long-tailed macaques. We used 2 experimental conditions that differed in the spatial distribution of a fixed amount of food (large vs. small patch). Though each condition induced contest competition, it was stronger in the small-patch condition. Arrival order does not correlate with dominance rank in either experimental condition. The α-male and α-female reached the feeding site 10-30 s after the beginning of the test. Some females seized on opportunities to reach the feeding site before them, especially in the large-patch condition. They used the early arrival tactic when the risks of aggression were relatively low, which subjects accomplished either by being dominant or by being nondominant but tolerated by the α-male. Social tolerance may provide individuals with an alternative means to obtain resources. In sum, variation in food abundance and distribution may affect the extent to which rank order determines order of arrival to feeding sites. A higher rank may confer priority in the choice of tactics, but not necessarily priority of access to the resources themselves.

Abstract: Abstract  We studied sex differences in the nature of aggression and dominance behaviour in two newly formed groups of 1-year-old Icelandic horses. One herd contained nine geldings, the other nine mares. The groups were matched with regard to dominance-determining traits such as age, weaning age, composition of native herd, social experience, genetic origin, body condition and maternal dominance status. High-ranking individuals of both sexes were more aggressive, high-ranking males were older, and high-ranking females had a better body condition. Frequencies of aggressions were similar in both groups. The mares reacted significantly more by showing submission upon an aggression rather than by not responding or by escalating the aggression. For the geldings, this difference was not observed due to a lower tendency to submit. A linear dominance hierarchy was found in both groups. David`s scores provided additional information regarding cardinal rank distances and were used to calculate steepness of hierarchies. The female hierarchy was somewhat steeper compared to the male hierarchy, suggesting somewhat lower despotism among males. This was mainly a consequence of the lower unidirectionality in male submission. Male contests occurred predominantly between dyads at top and mid positions, suggesting a low degree of acceptance of the hierarchy.

Abstract: 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 significantly 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 efficiently 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.

Abstract: Abstract  Many wild primates occupy large home ranges and travel long distances each day. Navigating these ranges to find sufficient food presents a substantial cognitive challenge, but we are still far from understanding either how primates represent spatial information mentally or how they use this information to navigate under natural conditions. In the course of a long-term socioecological study, we investigated and compared the travel paths of sympatric spider monkeys (Ateles belzebuth) and woolly monkeys (Lagothrix poeppigii) in Amazonian Ecuador. During several field seasons spanning an 8-year period, we followed focal individuals or groups of both species continuously for periods of multiple days and mapped their travel paths in detail. We found that both primates typically traveled through their home ranges following repeatedly used paths, or “routes”. Many of these routes were common to both species and were stable across study years. Several important routes appeared to be associated with distinct topographic features (e.g., ridgetops), which may constitute easily recognized landmarks useful for spatial navigation. The majority of all location records for both species fell along or near identified routes, as did most of the trees used for fruit feeding. Our results provide strong support for the idea that both woolly and spider monkey use route-based mental maps similar to those proposed by Poucet (Psychol Rev 100:163-182, 1993). We suggest that rather than remembering the specific locations of thousands of individual feeding trees and their phenological schedules, spider and woolly monkeys could nonetheless forage efficiently by committing to memory a series of route segments that, when followed, bring them into contact with many potential feeding sources for monitoring or visitation. Furthermore, because swallowed and defecated seeds are deposited in greater frequency along routes, the repeated use of particular travel paths over generations could profoundly influence the structure and composition of tropical forests, raising the intriguing possibility that these and other primate frugivores are active participants in constructing their own ecological niches. Building upon the insights of Byrne (Q J Exp Psychol 31:147-154, 1979, Normality and pathology in cognitive functions. Academic, London, pp 239-264, 1982) and Milton (The foraging strategy of howler monkeys: a study in primate economics. Columbia University Press, New York, 1980, On the move: how and why animals travel in groups. University of Chicago Press, Chicago, pp 375-417, 2000), our results highlight the likely general importance of route-based travel in the memory and foraging strategies of nonhuman primates.