Infant carrying by nulliparous female vervet monkeys (Cercopithecus aethiops).

We examined allomaternal behavior in vervet monkeys (Cercopithecus aethiops) in order to understand its developmental consequences. For 3 years before our study, all but 1 newborn infant had been removed. Thus, the animals had little experience with infants. During 2 summers and the intervening fall, we scored animals' proximity (     

Silhouettes elicit alarm calls from captive vervet monkeys (Cercopithecus aethiops).

In Part 1, alarm calls produced by captive vervets in response to naturally occurring stimuli were analyzed. Females and juveniles regularly alarm called to airplanes, birds, and barking dogs. Juvenile females accounted for 60% of these alarm calls. In Part 2, several monkeys from the colony were isolated and presented with life-sized silhouettes of a leopard, snake, eagle, baboon, vervet, and goose. Adult monkeys alarm called more than did juveniles. Alarm calls were elicited by leopard, snake, baboon, and vervet silhouettes, but none were elicited by eagle or goose silhouettes. Some leopard and snake alarm calls matched those recorded in the wild in the context of the vervets' natural predators. Results indicate that silhouette stimuli are a useful technique for eliciting monkey vocalizations in the laboratory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of foraging behavior in wild vervet monkeys (Cercopithecus aethiops): Social interactions and survival.

The ontogeny of feeding behavior was explored by making observations of 32 vervet monkey infants in Amboseli National Park, Kenya. In contrast to adults and juveniles, infants appear to treat all primary food products in their diet as equally valuable. These age-related differences may reflect differences in food preference. To assess social influences, feeding synchrony between mother and infant was explored. From birth to 2 mo, infants typically fed asynchronously with respect to their mother's feeding bouts. From 2–22 mo, however, most infants fed at the same time and on the same food items as their mothers. Among infants there was a significant positive association between the proportion of synchronous, same food bouts and the probability of survival. Variation among infants in access to resources and encounter rates with predators did not, however, have a significant effect on survival. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hand preferences in unimanual and coordinated-bimanual tasks by tufted capuchin monkeys (Cebus apella).

Hand preferences in 26 capuchin monkeys (Cebus apella) were examined in 2 reaching-for-food tasks under 2 postural conditions. In the 1st task (unimanual), monkeys were required to reach for food from both a quadrupedal and an upright posture. A right-hand bias was found for the upright but not for the quadrupedal condition. In the 2nd task (coordinated bimanual), monkeys were required to extract the food from a hanging Plexiglas tube from both a crouched and an upright posture. A right-hand bias was found for both conditions. A significant increase in right-hand use was noted from the unimanual, quadrupedal, reaching task to the coordinated-bimanual task, with females exhibiting a greater right-hand preference than males. In addition, a significant effect of task complexity on strength in laterality was found. Results are discussed in the context of recent theories on primate laterality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hand preference and performance on unimanual and bimanual tasks in capuchin monkeys (Cebus apella).

Patterns of manual preference and the extent to which preference provided a benefit in performance (movement time) were evaluated in 7 young adult capuchin monkeys (Cebus apella). Directions of preference were inconsistent within individual animals across home-cage activities, unimanual, and bimanual experimental tasks. Preferences were more strongly expressed in the experimental tasks than in the home cage. A left bias in the population for prehension, predicted by recent theories, was not evident in any setting. Movement time was moderately negatively correlated with degree of preference within experimental tasks. The benefit to performance conferred by lateral preference was not dependent on whether the right or the left hand was preferred. Lateralization of prehension appears to be a flexible process in these monkeys, which can result in quickly realized benefits in some conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acoustic classification of alarm calls by vervet monkeys (Cercopithecus aethiops) and humans (Homo sapiens): I. Natural calls.

A 2-choice, operant-conditioning-based classification procedure was developed in which vervet monkeys (Cercopithecus aethiops) categorized species-typical snake and eagle alarm calls recorded from individually identified free-ranging animals. After preliminary training with a pair of calls from a single animal, 2 vervets were tested with novel exemplars produced by a variety of callers. Experiment 1 combined testing with continued training in routine classification of 14 new calls. In Experiment 2, the Ss were tested with 48 novel calls in rapid succession. Human (Homo sapiens) control Ss participated in the 1st study without extended preliminary training. Monkey and human Ss both showed immediate transfer to classification of unfamiliar alarm calls, despite variations both in voice characteristics and reproduction quality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acoustic classification of alarm calls by vervet monkeys (Cercopithecus aethiops) and humans (Homo sapiens): II. Synthetic calls.

In 2 experiments classification of synthetic versions of species-typical snake and eagle alarm calls by vervet monkeys (Cercopithecus aethiops) and human (Homo sapiens) control Ss was investigated. In a 2-choice, operant-conditioning-based procedure, this work followed up acoustic analyses that had used various digitally based algorithms (M. J. Owren and R. H. Bernacki; see record 1989-10972-001). All Ss were first tested with alarm-call replicas that were based on analysis data. These models were classified in the same manner as natural stimuli, which verified the appropriateness of the acoustic charcterizations. Synthetic stimuli were then presented to test the importance of specific acoustic cues. Spectral patterning was found to be the most salient cue for classification by the monkeys, whereas results from the human Ss were mixed. Implications for the study of nonhuman primate vocalizations and P. Lieberman's (1984) theory of speech evolution are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogenetic changes in the comprehension and production of vervet monkey (Cercopithecus aethiops) vocalizations.

Factors underlying the development of the East African vervet monkeys' intergroup wrr vocalization were examined. Infants produced the intergroup wrr in appropriate social contexts between 10–28 months, but the acoustic morphology of this call differed significantly from those produced by adults. Auditory and social experience affected the age at which infants produced adult-like exemplars of the call, as well as the age at which they comprehended the call's meaning. Although the developmental time course for the production of intergroup wrrs is gradual, young infants (birth to 3 months) produce a wrr-like call in the context of distress which appears to be articulated in a more adult-like manner than older infants. It is hypothesized that maturational changes in vocal morphology, increasing motoric control and experience are important factors in the ontogeny of nonhuman primate vocal communication. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception of chirps by Sykes's monkeys (Cercopithecus albogularis) and humans (Homo sapiens).

Four Sykes's monkeys (Cercopithecus albogularis) and 4 humans (Homo sapiens) discriminated among 12 chirps presented in a repeating background paradigm. The test stimuli consisted of sets of 4 chirps recorded from Sykes's monkeys, red-tailed monkeys (C. ascanius), and small East African birds. Reaction times (RTs) were submitted to a multidimensional scaling analysis. All monkey listeners perceived the bird chirps as similar to each other and distinct from the monkey calls, whereas 3 of the 4 human listeners had difficulty distinguishing the bird chirps from the monkey calls. Both human and monkey subjects tended to perceive Sykes's and red-tailed monkey calls as very similar to one another, but the degree of perceived similarity was greatest for the monkey listeners. The data suggest that the perceptual map of these calls is influenced by their biological significance in nature. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Individual differences in response to a stranger: Social impulsivity as a dimension of temperament in vervet monkeys (Cercopithecus aethiops sabaeus).

Social impulsivity in response to a stranger was assessed in male vervet monkeys (Cercopithecus aethiops sabaeus) using the Intruder Challenge Test. Vervets (N?=?128, ages 3–18 years) were presented with an unfamiliar adult male at the periphery of the home enclosure. An index of impulsivity reflecting variation in the tendency to rapidly approach, engage, and challenge the intruder was derived from factor analysis of behavioral responses. Scale reliability (a?=?.84) and test–retest consistency (intraclass correlation?=?.83) were high, indicating that this index reliably and efficiently measures a stable aspect of temperament from impulsive to inhibited. Impulsivity scores peaked at age 4, when vervet males typically emigrate from the natal group. The highest ranking males in each group were more likely to score in the moderate range, whereas lower ranking males were more likely to score in the highest (impulsive) or lowest (inhibited) quartiles. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hand preference for a bimanual task in tufted capuchins (Cebus apella) and rhesus macaques (Macaca mulatta).

Examined hand preference for a bimanual task in 45 tufted capuchin (Cebus apella) and 55 rhesus macaque (Macaca mulatta) monkeys. Investigators presented subjects with plastic tubes lined with food and noted which hand the animals used to hold the tubes and which hand the animals used to remove the food. Several significant findings emerged from this investigation. First, rhesus macaques, but not tufted capuchins, exhibited a population-level bias toward use of the right hand (although the difference in direction of hand preference between species was not significant). Second, capuchins exhibited greater hand preference strength than did macaques. Third, among capuchins, but not among macaques, hand preference strength was greater for adults than for immatures. Finally, both species used their index digit to remove food most frequently when compared with other digits. Findings of hand preference direction and strength in this study were compared with other findings noted for chimpanzees which performed a bimanual tube task in a previous study. The authors conclude that using the same procedure to compare hand preference across species represents a powerful research tool that can lead to a more complete understanding of the evolution and ontogenesis of primate handedness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hand preferences for a coordinated bimanual task in 110 chimpanzees (Pan troglodytes): Cross-sectional analysis.

Hand preference for a coordinated bimanual task was assessed in a sample of 110 chimpanzees (Pan troglodytes). Subjects were presented with opaque tubes, the inside of which was coated with peanut butter. The hand and finger used to extract the peanut butter was recorded in 2 test sessions. A population right-hand bias was found. Juvenile and adolescent subjects were less lateralized than adults. All subjects primarily used their index finger to extract peanut butter. Use of the index finger was higher in adults and adolescents compared with juveniles. The results suggest that coordinated bimanual tasks (a) elicit strong hand preferences at the individual level and (b) elicit population level right-handedness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Socially Meaningful Vocal Plasticity in Adult Campbell's Monkeys (Cercopithecus campbelli).

Campbell's monkeys (Cercopithecus campbelli) frequently exchange vocalizations, the combined-harmonic calls, with individuals responding to one another's calls. Previous work has shown that these calls can be grouped into several structural variants. Adult females differ in their variant repertoires, which may change during their adult life, particularly after changes in the group composition. Playback of females' currently produced variants triggered vocal responses from other group members, whereas the same females' former, no longer used variants and those of stranger females never did. In contrast, former variants caused long-term cessation of vocal behavior, whereas stranger variants had no effect. Data showed that monkeys were able to distinguish between the different types of variants, indicating that these calls form part of a long-term social memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prototype abstraction by monkeys (Macaca mulatta).

The authors analyze the shape categorization of rhesus monkeys (Macaca mulatta) and the role of prototype- and exemplar-based comparison processes in monkeys' category learning. Prototype and exemplar theories make contrasting predictions regarding performance on the Posner-Homa dot-distortion categorization task. Prototype theory--which presumes that participants refer to-be-categorized items to a representation near the category's center (the prototype)--predicts steep typicality gradients and large prototype-enhancement effects. Exemplar theory--which presumes that participants refer to-be-categorized items to memorized training exemplars-predicts flat typicality gradients and small prototype-enhancement effects. Across many categorization tasks that, for the first time, assayed monkeys' dot-distortion categorization, monkeys showed steep typicality gradients and large prototype-enhancement effects. These results suggest that monkeys--like humans--refer to-be-categorized items to a prototype-like representation near the category's center rather than to a set of memorized training exemplars. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparisons of feeding behavior in captive squirrel and titi monkeys (Saimiri sciureus and Callicebus moloch).

In view of behavioral differences observed in natural environments, one might expect that feeding and foraging patterns draw on different behavioral tendencies in squirrel and titi monkeys. Some of these tendencies were identified in the present 4 studies. In the home cage and in the presence of abundant food, squirrel monkeys were rapid, wasteful, and relatively asocial feeders. Titis in the same setting were slower, more selective, thorough, and socially involved feeders. Passive sharing of food between titi pair-mates was common. When competition was increased by presenting a single food item, titis continued to rely on positive social interactions to obtain food; squirrel monkeys still relied mainly on asocial stratagems to obtain food. The species' food preferences in paired-comparison tests were quite similar, although their patterns of obtaining and consuming the foods were not. Squirrel monkeys took food more quickly but consumed less than titis. When the same foods were presented repetitively, squirrel monkeys remained more wasteful consumers and were satiated more quickly than titis, even with highly preferred foods. These differences are discussed in terms of their probable contributions to each species' modal foraging patterns in natural environments. The findings are placed in an adaptive profile framework for each species, based on data accumulated in a series of studies conducted over the last decade. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hand preference for food processing in wild western lowland gorillas (gorilla gorilla gorilla).

Western lowland gorillas (Gorilla gorilla gorilla) have not previously been represented in studies of laterality in wild great apes. The discovery of swampy clearings frequented by gorillas in northern Congo has provided the first opportunity to redress this imbalance. Hand preference data are presented from 33 gorillas in seated and standing postures, covering the procurement and processing of 2 to 4 plant species. Levels of hand preference exhibited were low. When data from all postures and plant species were pooled, 33% of gorillas showed hand preferences in excess of chance. In the standing posture, more gorillas exhibited significant left-hand preferences than right, but an overall population-level bias was not evident. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Use of olfactory cues in foraging by owl monkeys (Aotus nancymai) and capuchin monkeys (Cebus apella).

The authors tested free-ranging New World monkeys (nocturnal owl monkeys [Aotus nancymai] and diurnal capuchin monkeys [Cebus apella]) to determine the extent to which they use olfactory cues to locate food hidden in containers at 2 of 6 feeding sites within a 1?-ha forested enclosure. These 2 sites were selected randomly for each trial and then were baited with banana and banana peel residue. The 4 other sites were unbaited and unscented. In trials in which the food was not visible to the monkeys, Aotus monkeys located the baited sites at a level greater than expected by chance, whereas Cebus monkeys did not. Use of olfactory information by Aotus monkeys in foraging may be an adaptation for nocturnal foraging because olfactory cues are more salient than visual cues at low light levels. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Delay of gratification in capuchin monkeys (cebus apella) and squirrel monkeys (saimiri sciureus).

In two separate series of experiments four capuchin monkeys (Cebus apella) and four squirrel monkeys (Saimiri sciureus) were given demonstration trials in which a human transferred six pieces of food, one by one, from out of each monkey's reach to within reach. On test trials the monkey could reach for the transferred food at any time, an action that ended the trial. Therefore, it was in the monkey's interest to allow food items to accumulate before reaching for food. No capuchin monkey showed delay of gratification in the first phase of testing. An attempt to facilitate performance by presenting a single free food item immediately before the transfer failed (Phase 2). In Phase 3, when the transferred food items increased progressively in size, two capuchins maintained delays, and frequently waited for all 6 items to accumulate. One squirrel monkey started to delay gratification in Phase 1, and another did so in Phase 3. A return to single-sized food items did not impair the monkeys' ability to delay. Short (1 s) interitem delays were generally easier to maintain than longer delays (3 or 5 s). In both species the delaying individuals bridged the delays idiosyncratically. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of skilled detection and extraction of embedded prey by wild brown capuchin monkeys (cebus apella apella).

Brown capuchin monkeys (Cebus apella apella) in Suriname forage on larvae enclosed within healthy bamboo stalks. We applied the searching versus handling dichotomy of optimal foraging models to highlight developmental processes contributing to foraging on embedded prey. Larvae acquisition begins with search; selecting an appropriate stalk and locating the embedded larvae; followed by handling, ripping the stalk open, and extracting the larvae. Although extraction behaviors were present at low rates in infant capuchins' repertoire, we found that the acquisition of adequate detection techniques was fully completed in subadults, aged around 6. Selecting appropriate foraging substrates, requiring accurate assessment of the physical properties of bamboo stalks, gradually increased with age and experience. We showed that both components of searching required extended practice beyond that required to master the handling components. We conclude that the developmental sequence of skill acquisition goes counter to the preceding logical sequence of foraging process and suggest that searching components present greater challenges than handling components in extractive foraging. Specifying the searching components of foraging more precisely will enhance understanding of species variation in the developmental schedule of foraging skills. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Auditory frequency discrimination in primates: Species differences (Cercopithecus, Macaca, Homo).

Auditory frequency difference limens (DLs) at 2 kHz were measured in Old World monkeys (Cercopithecus, Macaca) and humans using a go/no-go repeating standard procedure and positive reinforcement operant conditioning techniques. Quantitative and qualitative differences occurred between monkey and human sensitivity. Best DLs for monkeys were 20–60 Hz, and for humans they were 3–4 Hz. Monkey sensitivity decreased as sensation level increased from 30 to 70 dB, whereas human sensitivity increased. Sensitivity differences also occurred in the various monkey species. Cercopithecus monkeys were generally more sensitive to frequency decrements, whereas Japanese macaques were more sensitive to frequency increments, as were humans. Results are related to other comparative psychoacoustic data and primate vocal communication, including human speech. (PsycINFO Database Record (c) 2010 APA, all rights reserved)