Infant socialization in Primates

This review considers evolutionary trends, functions, stages, and current issues in Primate socialization. The concept of social “set” is discussed in the context of the interactional nature of socialization, where the infant is regarded as a primary effector in its own socialization. Laboratory approaches and measurement techniques are reviewed briefly.     

Stone Anvil Damage by Wild Bearded Capuchins (Sapajus libidinosus) during Pounding Tool Use: A Field Experiment

We recorded the damage that wild bearded capuchin monkeys (Sapajus libidinosus) caused to a sandstone anvil during pounding stone tool use, in an experimental setting. The anvil was undamaged when set up at the Fazenda Boa Vista (FBV) field laboratory in Piauí, Brazil, and subsequently the monkeys indirectly created a series of pits and destroyed the anvil surface by cracking palm nuts on it. We measured the size and rate of pit formation, and recorded when adult and immature monkeys removed loose material from the anvil surface. We found that new pits were formed with approximately every 10 nuts cracked, (corresponding to an average of 38 strikes with a stone tool), and that adult males were the primary initiators of new pit positions on the anvil. Whole nuts were preferentially placed within pits for cracking, and partially-broken nuts outside the established pits. Visible anvil damage was rapid, occurring within a day of the anvil''s introduction to the field laboratory. Destruction of the anvil through use has continued for three years since the experiment, resulting in both a pitted surface and a surrounding archaeological debris field that replicate features seen at natural FBV anvils.     

Influence of a skilled model on the behavior of conspecific observers in tufted capuchin monkeys (Cebus apella)

We analyze how the presence of a skilled juvenile capuchin monkey interacting with a mechanical puzzle requiring sequential actions affected the behavior of group-mates towards the puzzle. Using this study as an example, we suggest a methodological approach to the evaluation of social enhancement of activity and imitation. We suggest that this design could be useful in determining if social and demographic factors influence the occurrence of these phenomena. © 1995 Wiley-Liss, Inc.     

Development of maze navigation by tufted capuchins (Cebus apella)

Theories of spatial navigation hypothesize that animals use vector or topological information to choose routes, often including detours, to move objects or themselves to goals. We assessed adult capuchin monkeys’ (Cebus apella) navigation through 192 virtual two-dimensional mazes that incorporated detour problems. Six monkeys initially were significantly less likely to choose the correct paths when detours were required than when not. Three of the six monkeys repeatedly practiced the 192 mazes to asymptotic mastery; the other three did not practice the mazes again. In a subsequent transfer test, each monkey made correct choices equivalently often on familiar and novel mazes, which suggests that they used general planning skills for maze navigation. Of the three monkeys that practiced the 192 maze-set repeatedly, one efficiently detoured and the other two significantly improved detouring compared to their initial performance. Two monkeys, contrary to their performance when completing the 192 maze-set for the first time, made correct choices at the same rate as chimpanzees. Some evidence suggested that two monkeys used topological information, but utilization of vector information was obvious for all monkeys. Our findings suggest that the boundaries of any individual's navigational abilities are not predicted by species, but depend on experience.     

Introduction and integration of strangers into captive groups of tufted capuchins (Cebus apella)

We introduced two to four unfamiliar animals into three established groups (N = 6–9 per group) of tufted capuchins (Cebus apella).We present findings on the behavioral consequences of introductions as a function of age, sex, and residency status and long-term consequences for health and reproduction. No morbidity from aggression occurred at the time of introductions or during several months following, and reproduction was not compromised. Activity budgets and patterns of social spacing and interaction were little changed following the introductions except for increases in vigilance behavior, especially by newly introduced adult females. Adult females exhibited the strongest and longest-lasting response to changes in group composition. The results indicate that in this species (1) introductions of adult females can be carried out with acceptable risk to the newcomers provided that careful monitoring occurs, so that the onset of severe aggression instigated by resident females toward new females can be avoided, (2) juveniles can be introduced with minimal risk, and (3) adult males can be introduced into groups lacking resident adult males with minimal risk. Capuchins differ in important ways from the better-studied Old World monkeys in their response to introductions of strangers. The differences are instructive with regard to processes supporting species-typical social structure, which is less overtly hierarchical in capuchins than in macaques.     

Comparison of Development and Life History in Pan and Cebus

We examined growth and development in capuchins and chimpanzees in relation to weaning, onset of reproduction, and reproductive life span. Striking differences are evident in neurobehavioral status at birth (more mature in capuchins), the relative duration of infancy (longer in chimpanzees), and the proportional weight of the infant at the time of weaning (greater in capuchins). Although capuchins and chimpanzees spend a similar proportion of life in a weaned but reproductively immature state, chimpanzees spend so much more of their lives as nursing infants that reproductive output per individual is much lower than in capuchins. Discussion centers around tolerated transfers of food (food-sharing) as a potential adaptation to limited foraging success by immature foragers. Perhaps food transfers from adult to infant, which is a more prominent feature of behavior in chimpanzees than in capuchins in natural environments, allow a very small weanling chimpanzee to survive.     

Characteristics of hammer stones and anvils used by wild bearded capuchin monkeys (Cebus libidinosus) to crack open palm nuts

Capuchins living in Boa Vista (Piauì, Brazil) crack open hard palm nuts on hard, level surfaces (anvils) using stones (hammers) as percussive tools. This activity leaves diagnostic physical remains: distinctive shallow depressions (pits) on the surface of the anvil, cracked shells, and stone hammers on the anvil. To initiate comparison of percussive stone tool use and interpretation of the artifacts it produces across capuchins, chimpanzees, and hominins, we describe a sample of the anvils and hammer stones used by capuchin monkeys at our site. Anvils (boulders and logs) were located predominantly in the transition zone between the flat open woodland and ridges, in locations that offered some overhead coverage, and with a tree nearby, but not necessarily near palm trees. Anvils contained shallow, hemispherical pits with smooth interiors. Hammers represent a diverse assemblage of ancient rocks that are much harder than the prevailing sedimentary rock out of which they eroded. Hard stones large enough to serve as hammers were more abundant on the anvils than in the surrounding area, indicating that capuchins transport them to the anvils. Capuchins use hammers weighing on average more than 1 kg, a weight that is equivalent to 25-40% of the average body weight for adult males and females. Our findings indicate that capuchins select stones to use as hammers and transport stones and nuts to anvil sites. Wild capuchins provide a new reference point for interpreting early percussive stone tool use in hominins, and a point of comparison with chimpanzees cracking nuts.