Adult Chimpanzees Research Articles

Social bonds in the dispersing sex: partner preferences among adult female chimpanzees

In most primate societies, strong and enduring social bonds form preferentially among kin, who benefit from cooperation through direct and indirect fitness gains. Chimpanzees, Pan troglodytes, differ from most species by showing consistent female-biased dispersal and strict male philopatry. In most East African populations, females tend to forage alone in small core areas and were long thought to have weak social bonds of little biological significance. Recent work in some populations is challenging this view. However, challenges remain in quantifying the influence of shared space use on association patterns, and in identifying the drivers of partner preferences and social bonds. Here, we use the largest data set on wild chimpanzee behaviour currently available to assess potential determinants of female association patterns. We quantify pairwise similarities in ranging, dyadic association and grooming for 624 unique dyads over 38 years, including 17 adult female kin dyads. To search for social preferences that could not be explained by spatial overlap alone, we controlled for expected association based on pairwise kernel volume intersections of core areas. We found that association frequencies among females with above-average overlap correlated positively with grooming rates, suggesting that associations reflected social preferences in these dyads. Furthermore, when available, females preferred kin over nonkin partners for association and grooming, and variability was high among nonkin dyads. While variability in association above and below expected values was high, on average, nonkin associated more frequently if they had immature male offspring, while having female offspring had the opposite effect. Dominance rank, an important determinant of reproductive success at Gombe, influenced associations primarily for low-ranking females, who associated preferentially with each other. Our findings support the hypothesis that female chimpanzees form well-differentiated social relationships that are of potential adaptive value to females and their offspring.

Long-term effects of infant attachment organization on adult behavior and health in nursery-reared, captive chimpanzees (Pan troglodytes).

This research traces the long-term effects on health, well-being, personality, and behavior of adult chimpanzees as a function of their attachment to a primary human caregiver assessed when they were 1 year of age. Of the 46 chimpanzees assessed at 1 year of age, we assessed health in 43 individuals, adult behavior in 20 individuals, and adult well-being and personality in 21 individuals. Attachment disorganization was found to be a significant predictor of stereotypic rocking in adult chimpanzees, F(1, 18) = 7.50, p = .013. For those subjects (N = 24) with a full 20 years (birth through age 20 years) of health data available, both rearing experience and disorganized attachment were significant predictors of upper respiratory infection frequency, F(2, 21) = 8.86, p = .002. Chimpanzees with disorganized attachment exhibited average subjective well-being as adults, whereas chimpanzees with organized strategies exhibited higher than average subjective well-being as adults. These results support the findings of human attachment research and are in line with attachment-based predictions for chimpanzees, such that the consequences of an early history of disorganized attachment may be adverse and long lasting.

Single aggressive interactions increase urinary glucocorticoid levels in wild male chimpanzees.

A basic premise in behavioural ecology is the cost-benefit arithmetic, which determines both behavioural decisions and evolutionary processes. Aggressive interactions can be costly on an energetic level, demanding increased energy or causing injuries, and on a psychological level, in the form of increased anxiety and damaged relationships between opponents. Here we used urinary glucocorticoid (uGC) levels to assess the costs of aggression in wild chimpanzees of Budongo Forest, Uganda. We collected 169 urine samples from nine adult male chimpanzees following 14 aggressive interactions (test condition) and 10 resting events (control condition). Subjects showed significantly higher uGC levels after single aggressive interactions compared to control conditions, likely for aggressors as well as victims. Higher ranking males had greater increases of uGC levels after aggression than lower ranking males. In contrast, uGC levels showed no significant change in relation to aggression length or intensity, indicating that psychological factors might have played a larger role than mere energetic expenditure. We concluded that aggressive behaviour is costly for both aggressors and victims and that costs seem poorly explained by energetic demands of the interaction. Our findings are relevant for studies of post-conflict interactions, since we provide evidence that both aggressors and victims experience a stress response to conflict.

Vocal Learning in the Functionally Referential Food Grunts of Chimpanzees

One standout feature of human language is our ability to reference external objects and events with socially learned symbols, or words. Exploring the phylogenetic origins of this capacity is therefore key to a comprehensive understanding of the evolution of language. While non-human primates can produce vocalizations that refer to external objects in the environment, it is generally accepted that their acoustic structure is fixed and a product of arousal states. Indeed, it has been argued that the apparent lack of flexible control over the structure of referential vocalizations represents a key discontinuity with language. Here, we demonstrate vocal learning in the acoustic structure of referential food grunts in captive chimpanzees. We found that, following the integration of two groups of adult chimpanzees, the acoustic structure of referential food grunts produced for a specific food converged over 3 years. Acoustic convergence arose independently of preference for the food, and social network analyses indicated this only occurred after strong affiliative relationships were established between the original subgroups. We argue that these data represent the first evidence of non-human animals actively modifying and socially learning the structure of a meaningful referential vocalization from conspecifics. Our findings indicate that primate referential call structure is not simply determined by arousal and that the socially learned nature of referential words in humans likely has ancient evolutionary origins.

Cortical structure of hallucal metatarsals and locomotor adaptations in hominoids.

Diaphyseal morphology of long bones, in part, reflects in vivo loads experienced during the lifetime of an individual. The first metatarsal, as a cornerstone structure of the foot, presumably expresses diaphyseal morphology that reflects loading history of the foot during stance phase of gait. Human feet differ substantially from those of other apes in terms of loading histories when comparing the path of the center of pressure during stance phase, which reflects different weight transfer mechanisms. Here we use a novel approach for quantifying continuous thickness and cross-sectional geometric properties of long bones in order to test explicit hypotheses about loading histories and diaphyseal structure of adult chimpanzee, gorilla, and human first metatarsals. For each hallucal metatarsal, 17 cross sections were extracted at regularly-spaced intervals (2.5% length) between 25% and 65% length. Cortical thickness in cross sections was measured in one degree radially-arranged increments, while second moments of area were measured about neutral axes also in one degree radially-arranged increments. Standardized thicknesses and second moments of area were visualized using false color maps, while penalized discriminant analyses were used to evaluate quantitative species differences. Humans systematically exhibit the thinnest diaphyseal cortices, yet the greatest diaphyseal rigidities, particularly in dorsoplantar regions. Shifts in orientation of maximum second moments of area along the diaphysis also distinguish human hallucal metatarsals from those of chimpanzees and gorillas. Diaphyseal structure reflects different loading regimes, often in predictable ways, with human versus non-human differences probably resulting both from the use of arboreal substrates by non-human apes and by differing spatial relationships between hallux position and orientation of the substrate reaction resultant during stance. The novel morphological approach employed in this study offers the potential for transformative insights into form-function relationships in additional long bones, including those of extinct organisms (e.g., fossils).

Relation between the level of self-mutilation and theconcentration of fecal metabolites of glucocorticoids incaptive chimpanzees (Pan troglodytes)

The influence of stress in an environment, according with the behavioral and endocrine variables of primates, are increasingly being studied by a diversity of authors, and have shown that abnormal behaviors associated with increased glucocorticoids may be directly related with the impairment of their well-being. In this work were used 22 adult chimpanzees (Pan troglodytes), 11 males and 11 females, kept in captivity in three different institutions. All animals had their behavior registered by focal session using a 30 seconds sample interval, during six months, totaling 4,800 registries per each animal. During this period, fecal samples were collected 3 times a week for the extraction and measurement of the concentration of fecal metabolites of glucocorticoid by radioimmunoassay. Of the total observed, stereotypical behaviors represented 13,45±2.76%, and among them, self-mutilation represented 38.28±3.98 %. The animals were classified into three different scores, according with the percentage of body surface with alopecia due to self-mutilation. It was found a positive correlation of high intensity between the scores of alopecia due to the observed mutilation and the average concentrations of fecal metabolites of glucocorticoids. This result strongly suggests that this measurement of self-mutilation in a chimpanzee can be used as an important auxiliary tool to evaluate de conditions of adaptation of an animal in captivity, functioning as a direct indicator of the presence of chronic stress.

Egalitarian despots: hierarchy steepness, reciprocity and the grooming-trade model in wild chimpanzees, Pan troglodytes

Biological market theory models the action of natural selection as a marketplace in which animals are viewed as traders with commodities to offer and exchange. Studies of female Old World monkeys have suggested that grooming might be employed as a commodity to be reciprocated or traded for alternative services, yet previous tests of this grooming-trade model in wild adult male chimpanzees have yielded mixed results. Here we provide the strongest test of the model to date for male chimpanzees: we use data drawn from two social groups (communities) of chimpanzees from different populations and give explicit consideration to variation in dominance hierarchy steepness, as such variation results in differing conditions for biological markets. First, analysis of data from published accounts of other chimpanzee communities, together with our own data, showed that hierarchy steepness varied considerably within and across communities and that the number of adult males in a community aged 20-30 years predicted hierarchy steepness. The two communities in which we tested predictions of the grooming-trade model lay at opposite extremes of this distribution. Second, in accord with the grooming-trade model, we found evidence that male chimpanzees trade grooming for agonistic support where hierarchies are steep (despotic) and consequent effective support is a rank-related commodity, but not where hierarchies are shallow (egalitarian). However, we also found that grooming was reciprocated regardless of hierarchy steepness. Our findings also hint at the possibility of agonistic competition, or at least exclusion, in relation to grooming opportunities compromising the free market envisioned by biological market theory. Our results build on previous findings across chimpanzee communities to emphasize the importance of reciprocal grooming exchanges among adult male chimpanzees, which can be understood in a biological markets framework if grooming by or with particular individuals is a valuable commodity.

Wild chimpanzees plan their breakfast time, type, and location.

Not all tropical fruits are equally desired by rainforest foragers and some fruit trees get depleted more quickly and carry fruit for shorter periods than others. We investigated whether a ripe-fruit specialist, the chimpanzee (Pan troglodytes verus), arrived earlier at breakfast sites with very ephemeral and highly sought-after fruit, like figs, than sites with less ephemeral fruit that can be more predictably obtained throughout the entire day. We recorded when and where five adult female chimpanzees spent the night and acquired food for a total of 275 full days during three fruit-scarce periods in a West African tropical rainforest. We found that chimpanzees left their sleeping nests earlier (often before sunrise when the forest is still dark) when breakfasting on very ephemeral fruits, especially when they were farther away. Moreover, the females positioned their sleeping nests more in the direction of the next day's breakfast sites with ephemeral fruit compared with breakfast sites with other fruit. By analyzing departure times and nest positioning as a function of fruit type and location, while controlling for more parsimonious explanations, such as temperature, we found evidence that wild chimpanzees flexibly plan their breakfast time, type, and location after weighing multiple disparate pieces of information. Our study reveals a cognitive mechanism by which large-brained primates can buffer the effects of seasonal declines in food availability and increased interspecific competition to facilitate first access to nutritious food. We discuss the implications for theories on hominoid brain-size evolution.

From colour photographs to black-and-white line drawings: an assessment of chimpanzees' (Pan troglodytes') transfer behaviour.

Over two experiments, we investigated the ability of two adolescent and two adult chimpanzees to generalise a learnt, pictorial categorisation to increasingly degraded and abstract stimuli. In Experiment 2, we further assessed the ability of the adolescent chimpanzees to engage in open-ended categorisation of black-and-white line drawings. The current results confirmed and extended previous findings, showing that sub-adult chimpanzees outperform adult chimpanzees in the categorisation of pictorial stimuli, particularly when the stimuli are more degraded and abstract in nature. However, none of the four chimpanzees showed positive transfer of their category learning to a set of black-and-white line drawings, and neither of the adolescent chimpanzees evidenced reliable open-ended categorisation of the black-and-white line drawings. The latter findings suggest that both sub-adult and adult chimpanzees find it difficult to recognise black-and-white line drawings, and that open-ended categorisation of black-and-white line drawings is challenging for chimpanzees.

A pilot study on the effects of a change in behavioural management on the behaviour of captive chimpanzees (Pan troglodytes)

The debate on the use of chimpanzees (Pan troglodytes) in biomedical research has been ongoing for several years now. In 2012, the decision was made to retire a large number of laboratory chimpanzees in the United States of America. Relocation of these animals to sanctuaries, rescue centres, and zoos involve several changes in environment and husbandry routines. Because these animals often have a history of maternal deprivation, and consequently may suffer from an increased sensitivity to stress, these management changes may affect their behaviour. In The Netherlands, six groups of adult chimpanzees (n=28), which were removed from their mother when juvenile and were hand or peer reared, were relocated from a biomedical laboratory to substantially larger enclosures at a Dutch sanctuary. This sanctuary applied different animal management routines. It was studied whether long-term agonistic, affiliative, and abnormal behaviour was affected by the relocation and alteration in behavioural management. The chimpanzees’ behaviour was observed at the laboratory and during four years at the sanctuary, which resulted in 309h of observational data. Results indicated that the chimpanzees performed more allogrooming and less aggressive interactions at the sanctuary compared to the laboratory. However, abnormal behaviour was performed more often at the sanctuary. These results suggest that additional measures should be taken to enhance the welfare level of chimpanzees, at least for those that have a history of maternal deprivation.

Spatial cohesion of adult male chimpanzees (Pan troglodytes verus) in Taï National Park, Côte d'Ivoire.

Group living animals can exhibit fission-fusion behavior whereby individuals temporarily separate to reduce the costs of living in large groups. Primates living in groups with fission-fusion dynamics face numerous challenges in maintaining spatial cohesion, especially in environments with limited visibility. Here we investigated the spatial cohesion of adult male chimpanzees (Pan troglodytes verus) living in Taï National Park, Côte d'Ivoire, to better understand the mechanisms by which individuals maintain group cohesion during fission-fusion events. Over a 3-year period, we simultaneously tracked the movements of 2-4 males for 4-12 hr on up to 12 consecutive days using handheld GPS devices that recorded locations at one-minute intervals. Analyses of the male's inter-individual distance (IID) showed that the maximum, median, and mean IID values across all observations were 7.2 km, 73 m, and 483 m, respectively. These males (a) had maximum daily IID values below the limits of auditory communication (<1 km) for 63% of the observation time, (b) remained out of visual range (≥100 m) for 46% of observation time, and (c) remained within auditory range for 70% of the time when they were in different parties. We compared the observed distribution of IIDs with a random distribution obtained from permutations of the individuals' travel paths using Kolmogorov-Smirnov tests. Observation IID values were significantly smaller than those generated by the permutation procedure. We conclude that these male chimpanzees actively maintain cohesion when out of sight, and that auditory communication is one likely mechanism by which they do so. We discuss mechanisms by which chimpanzees may maintain the level of cohesion observed. This study provides a first analysis of spatial group cohesion over large distances in forest chimpanzees using high-resolution tracking, and illustrates the utility of such data for quantifying socio-ecological processes in primate ecology.

Social and nonsocial category discriminations in a chimpanzee (Pan troglodytes) and American black bears (Ursus americanus).

One captive adult chimpanzee and 3 adult American black bears were presented with a series of natural category discrimination tasks on a touch-screen computer. This is the first explicit comparison of bear and primate abilities using identical tasks, and the first test of a social concept in a carnivore. The discriminations involved a social relationship category (mother/offspring) and a nonsocial category involving food items. The social category discrimination could be made using knowledge of the overarching mother/offspring concept, whereas the nonsocial category discriminations could be made only by using perceptual rules, such as "choose images that show larger and smaller items of the same type." The bears failed to show above-chance transfer on either the social or nonsocial discriminations, indicating that they did not use either the perceptual rule or knowledge of the overarching concept of mother/offspring to guide their choices in these tasks. However, at least 1 bear remembered previously reinforced stimuli when these stimuli were recombined, later. The chimpanzee showed transfer on a control task and did not consistently apply a perceptual rule to solve the nonsocial task, so it is possible that he eventually acquired the social concept. Further comparisons between species on identical tasks assessing social knowledge will help illuminate the selective pressures responsible for a range of social cognitive skills.

Subspecies identification of Chimpanzees Pan troglodytes (Primates: Hominidae) from the National Zoo of the Metropolitan Park of Santiago, Chile, using mitochondrial DNA sequences

Natural populations of Chimpanzees Pan troglodytes are declining because of hunting and illegal live animal trafficking. Four subspecies of Chimpanzee have been reported: Pan troglodytes troglodytes, P.t. schweinfurthii, P.t. verus and P.t. ellioti, which have remained geographically separated by natural barriers such as the rivers Niger, Sanaga and Ubangi in central Africa. Sequence analysis of mitochondrial DNA (mtDNA) has been used for the determination of these subspecies, which indirectly can also suggest their geographic origin. It was decided to identify the subspecies and the geographic origin of three captive chimpanzees of the National Zoo of the Metropolitan Park of Santiago (Chile), by analyzing their mitochondrial DNA. DNA was extracted from the saliva of three adult chimpanzees (two males and one female). After the analysis of sequences of the mitochondrial hypervariable region (HVI), a phylogenetic tree was constructed using mitochondrial sequences of known Pan troglodytes subspecies. Molecular phylogeny analysis revealed that the chimpanzees are likely to belong to three different subspecies: P.t. schweinfurthii, P.t. verus and P.t. troglodytes. Identification of subspecies of the three chimpanzees of the National Zoo of the Metropolitan Park of Santiago (Chile) was possible due to mtDNA analysis. Future identification of chimpanzees will allow the development of a studbook for the chimpanzee subspecies in other Latin American zoos.

Echocardiography parameters of clinically normal adult captive chimpanzees (Pan troglodytes)

To generate reference ranges for echocardiographic variables in clinically normal adult chimpanzees (Pan troglodytes). Retrospective cohort study. 88 clinically normal adult chimpanzees. Echocardiographic data obtained between 2002 and 2011 from chimpanzees at the Alamogordo Primate Facility were reviewed (263 echocardiograms obtained from 158 individuals). Data from clinically normal individuals (33 females and 55 males) were analyzed. Basic cardiac parameters measured in all individuals included aortic root diameter and left atrial diameter in the short and long axis during diastole. Left ventricular measurements included left ventricular internal diameter in systole and diastole and diastolic septal and posterior wall thickness. The E point to septal separation was also measured. Spectral Doppler measurements included the peak flow velocity of the pulmonary artery and aorta and diastolic transmitral flow. The presence of arrhythmias was also noted. Standard echocardiographic findings for a large group of adult female and male chimpanzees were obtained. Female and male chimpanzees were grouped by age in 10-year blocks, and echocardiographic findings were analyzed statistically by 10-year block. In male chimpanzees, cardiac arrhythmias were noted to increase with age. Cardiovascular disease is an important cause of morbidity and death in captive chimpanzees; however, basic echocardiographic measurements from a large cohort of clinically normal animals have not previously been reported. The number of animals in the present study was insufficient to generate reference ranges; however, data from a large cohort of clinically normal animals are presented. This information will be useful for veterinarians working in clinical and research settings with this species.

Interspecific comparison of ontegenetic change in temporal bone pneumatization (918.22)

Comparative studies of temporal bone pneumatization in adult chimpanzees and modern humans have shown that human temporal bones have reduced pneumatization compared to chimpanzee temporal bones, following the general trend towards reduction in pneumatization over the course of hominid evolution. Although the adult pattern of pneumatization in chimpanzees is well studied, extensive quantitative comparisons of the ontogenetic change in pneumatization of the temporal bone in chimpanzees and modern humans have not been completed. The purpose of this study is to compare patterns of ontogenetic change in temporal bone pneumatization in humans and chimpanzees.High resolution computed tomography scans were acquired from cross‐sectional ontogenetic series of human (n=29) and chimpanzee (n =30) temporal bones. The sample included individuals ranging in age from neonate to adult for both species. Surface areas and volumes of the temporal bone air cell tracts were calculated using Amira for both species.Results indicate that, from an early age, chimpanzees show larger surface areas and volumes of the temporal bone air cell tracts compared to modern humans. Although there are some differences in timing of pneumatization in the two species, these differences in size may result from the progression of the air cells from both the mastoid and squamous antrums in chimpanzees. This study highlights the early establishment of adult size differences in pneumatization.

Development of adrenal cortical zonation and expression of key elements of adrenal androgen production in the chimpanzee (Pan troglodytes) from birth to adulthood

The basis for the pattern of adrenal androgen production in the chimpanzee, which resembles that of humans, is poorly defined. We characterized the developmental zonation and expression of elements of the androgen biosynthetic pathway in the chimpanzee adrenal. The newborn adrenal contained a broad fetal zone (FZ) expressing CYP17, SULT2A1, and Cytochrome B5 (CB5) but not HSD3B; the outer cortex expressed HSD3B but not SULT2A1 or CB5. During infancy, the FZ involuted and the HSD3B-expressing outer cortex broadened. By 3years of age, a thin layer of cells that expressed CB5, SULT2A1, and CYP17 adjoined the medulla and likely represented the zona reticularis; the outer cortex consisted of distinct zonae fasiculata and glomerulosa. Thereafter, the zona reticularis broadened as also occurs in the human. The adult chimpanzee adrenal displayed other human-like characteristics: intramedullary clusters of reticularis-like cells and also a cortical cuff of zona fasiculata-like cells adjoining the central vein.

Chimpanzee diet: Phytolithic analysis of feces

Most primate populations remain unobservable; therefore, researchers depend on the analyses of indirect evidence encountered at a study-site in order to understand their behavioral ecology. Diet can be determined through the analyses of scats or feeding remains encountered on-site. This allows aspects of their dietary repertoire to be established, which has implications both for conservation efforts (by locating food resources), and for understanding the evolution of hominin diet (if used as referential models). Macroscopic inspection of fecal samples is a common method applied to ascertain a primate population's diet. However, new approaches are required to identify food-items unrecognizable at this level. We applied a dry ash extraction method to fecal samples (N=50) collected from 10 adult chimpanzees in Kanyawara, Kibale National Park, Uganda and also to plant parts (N=66) from 34 species known to be included in the diet of this community of apes. We recovered phytoliths in 26 of the 34 plant species. Fifteen phytolith morphotypes were only detected in 14 plant species (termed "distinct" phytoliths). We used these distinct phytoliths to identify plant foods (i.e., that they were associated with) in fecal samples. We then validated findings by checking if the 10 chimpanzees had eaten parts of these plants ∼24 hr prior to fecal sample collection; six plant species associated with five distinct phytoliths had been eaten. Finally, we compared plant foods identified in fecal samples from phytolith analyses with plants that had been identified from macroscopic inspection of the same fecal samples. Findings from phytolith analyses corroborate with those from macroscopic inspection by expanding the total number of plant species identified per fecal sample (i.e., we identified certain plant parts that remained unrecognizable at macroscopic level). This study highlights the potential of phytolith analyses of feces to increase our knowledgebase of the dietary repertoire of primate populations.

Tradition over trend: Neighboring chimpanzee communities maintain differences in cultural behavior despite frequent immigration of adult females

The notion of animal culture has been well established mainly through research aiming at uncovering differences between populations. In chimpanzees (Pan troglodytes verus), cultural diversity has even been found in neighboring communities, where differences were observed despite frequent immigration of individuals. Female chimpanzees transfer at the onset of sexual maturity at an age, when the behavioral repertoire is fully formed. With immigrating females, behavioral variety enters the group. Little is known about the diversity and the longevity of cultural traits within a community. This study is building on previous findings of differences in hammer selection when nut cracking between neighboring communities despite similar ecological conditions. We now further investigated the diversity and maintenance of cultural traits within one chimpanzee community and were able to show high levels of uniformity in group-specific behavior. Fidelity to the behavior pattern did not vary between dispersing females and philopatric males. Furthermore, group-specific tool selection remained similar over a period of 25 years. Additionally, we present a study case on how one newly immigrant female progressively behaved more similar to her new group, suggesting that the high level of similarity in behavior is actively adopted by group members possibly even when originally expressing the behavior in another form. Taken together, our data support a cultural transmission process in adult chimpanzees, which leads to persisting cultural behavior of one community over time.

Macroscopic inspection of ape feces: What's in a quantification method?

Macroscopic inspection of feces has been used to investigate primate diet. The limitations of this method to identify food-items to species level have long been recognized, but ascertaining aspects of diet (e.g., folivory) are achievable by quantifying food-items in feces. Quantification methods applied include rating food-items using a scale of abundance, estimating their percentage volume, and weighing food-items. However, verification as to whether or not composition data differ, depending on which quantification method is used during macroscopic inspection, has not been done. We analyzed feces collected from ten adult chimpanzees (Pan troglodytes schweinfurthii) of the Kanyawara community in Kibale National Park, Uganda. We compare dietary composition totals obtained from using different quantification methods and ascertain if sieve mesh size influences totals calculated. Finally, this study validates findings from direct observation of feeding by the same individuals from whom the fecal samples had been collected. Contrasting diet composition totals obtained by using different quantification methods and sieve mesh sizes can influence folivory and frugivory estimates. However, our findings were based on the assumption that fibrous matter contained pith and leaf fragments only, which remains to be verified. We advocate macroscopic inspection of feces can be a valuable tool to provide a generalized overview of dietary composition for primate populations. As most populations remain unhabituated, scrutinizing and validating indirect measures are important if they are to be applied to further understand inter- and intra-species dietary variation.

Using virtual reality to investigate comparative spatial cognitive abilities in chimpanzees and humans.

The purpose of the present study was to determine the efficacy of investigating spatial cognitive abilities across two primate species using virtual reality. In this study, we presented four captive adult chimpanzees and 16 humans (12 children and 4 adults) with simulated environments of increasing complexity and size to compare species' attention to visuo-spatial features during navigation. The specific task required participants to attend to landmarks in navigating along routes in order to localize the goal site. Both species were found to discriminate effectively between positive and negative landmarks. Assessing path efficiency revealed that both species and all age groups used relatively efficient, distance reducing routes during navigation. Compared to the chimpanzees and adult humans however, younger children's performance decreased as maze complexity and size increased. Surprisingly, in the most complex maze category the humans' performance was less accurate compared to one female chimpanzee. These results suggest that the method of using virtual reality to test captive primates, and in particular, chimpanzees, affords significant cross-species investigations of spatial cognitive and developmental comparisons.