PSGB Spring Meeting 1999

Primate Society of Great Britain

Spring Meeting, 12-13th April 1999

Liverpool University

ABSTRACTS

A. Special Session on Social Complexity

R.I.M. Dunbar (School of Biological Sciences, Liverpool University) & Hiroko Kudo (Kanagawa Prefectural Museum of Natural History, Odawara, Japan)

Neocortex size and the size of grooming cliques

Group size has been shown to correlate with relative neocortex size in primates, carnivores, cetaceans and some insectivores. This relationship may be mediated by a number of alternative behavioural processes, including the skills with which animals are able to manage their relationships with other group members. Since coalitions are known to be an important feature of primate social groups, we might predict a relationship between neocortex size and the size of the alliances that individuals can maintain. We test this hypothesis using data from a wide range of primates, including modern humans. We index alliance size by the size of grooming cliques (defined as the number of individuals groomed at a rate higher than the average were all grooming bouts evenly distributed among all potential dyads of adults in the group). We show that grooming clique is indeed a function of neocortex size. Moreover, clique size is linearly related to network size (the number of animals that can be reached, directly or indirectly, by relationships defined as above) and that network size is a more or less constant function of total group size.

Juan Carlos Gómez (School of Psychology, University of St.Andrews)

Complex communication in primates: Can rudiments of referential/ostensive communication be found in non-human primates?

A fundamental feature of human communication is the ability to refer to things without or beyond the use of coded systems such as language. In this paper I explore the possibility of tracing some origins of this ability &emdash; dubbed ‘referential-ostensive’ communication &emdash; in non-human primates, notably apes. Early experiments by E. Menzel (1971) suggested that chimpanzees are capable of developing ways of transmitting information about the location of targets that appear to be rudimentary referential. Studies with hand-reared apes suggest that these referential behaviours may rely upon the monitoring and management of joint attention, in a similar (but not identical) way to human infants who start their communicative careers with pre-linguistic gestures. I will review recent conflicting experimental evidence about the extent to which apes possess some of the abilities necessary for referential-ostensive communication. I will suggest that this evidence justifies attributing to apes a relatively complex communication system which can be properly termed ‘referential’ and ‘ostensive’, despite the intriguing differences that are apparent even when it is compared with the more rudimentary versions shown by human children.

 Filippo Aureli (Living Links Center, Emory University, USA)

Valuable relationships, anxiety and conflict resolution

Primates negotiate their conflicts in a variety of ways. Much research has focused on a specific mechanism, namely reconciliation, i.e. post-conflict friendly reunion between former opponents. Primates reconcile at different rates depending on the value of the relationship with the opponent. This flexibility may be mediated by emotions such as anxiety. Recent research has documented changes in anxiety during conflict and its resolution. Anxiety levels of both opponents are elevated following conflict, and post-conflict friendly reunions reduce anxiety at baseline levels. A model and a test of the mediating role of anxiety are presented to account for the influence of relationship quality on reconciliation. The model is also extended to those social mechanisms that prevent conflict from escalating in the first place.

Tracey H. Joffe (Department of Anthropology, University College London)

Bringing up baby: foetal and infant brain size ontogeny

Over the past 2 million years, humans have undergone a dramatic increase in relative brain size. Along with brain expansion, energetic costs associated with brain metabolism and, in particular, brain growth have increased significantly. Yet, basal metabolic rate in humans is no higher than expected for a mammal of our body size. Here I suggest that the additional metabolic costs of brain growth in highly encephalised humans are offset by a concomitant reduction in the size of a number of metabolically expensive organs during ontogeny and the metabolic interplay and flexibility of the maternal-conceptus unit. Fetal and infant biometric measures in humans and rhesus monkeys are used to construct longitudinal brain growth curves and to calculate residual brain size measures in these species. Preliminary findings in rhesus macaques and humans show that from the early stages of development, males have larger brain sizes than females when correcting for differences in body size. Organ sexual dimorphism is not, however, restricted to the brain but is present in a number of organs including the adrenals, spleen, thymus, liver and kidneys. A number of maternal parameters which relate to basal metabolic rate show no correlation with residual brain size in offspring. Results from multivariate analysis of necropsy data in rhesus macaques suggest that there is a close inverse relationship between residual brain size and adrenal gland size. This hints at an hormonal basis for brain size sexual dimorphism. In non-human studies there is evidence to suggest that high testosterone levels in the male fetus may play an important role in DNA and protein synthesis in a number of brain parts, while high estrogen levels associated with the large adrenals of the female fetus, may impede the binding of testosterone in the brain. The early surge in male testosterone levels may account for early sexual dimorphism in brain size. Additional analyses show that there are clear tradeoffs in size between residual brain weight and a number of other organs weights in rhesus macaque males. However, an organ size trade-off in females is less clear. This organ size/metabolic trade-off may explain how the additional metabolic demands for human brain growth are met. In addition, it suggests that maternal BMR may not constrain the growth of our large brain directly.

Colleen M. Schaffner (Department of Psychology, College of St.Benedict/St. John's University, Collegeville, USA)

Clever decisions: male and female marmosets' responses to reproductive competitors.

Marmosets and tamarins are cooperatively breeding monkeys that live peacefully in undisturbed family groups. However, breeding individuals occasionally cope with the presence of reproductive competitors. I will report on two studies in which males and females are challenged by rivals. In the first study, breeding females from small and large family groups were exposed to male and female intruders. Resident females were aggressive to female intruders, but only when family groups were large. In the second study, pairs of related and unrelated males lived together and their behavior was monitored under undisturbed conditions and during periods with limited resource availability, which included food trials and introduction to a female. Although dyads were stable when living alone, regardless of relatedness, only related males formed stable groups with females. These 'decisions' serve to reduce competition and promote pacific living within family groups.

A. Whiten (School of Psychology, University of St Andrews)

Mind reading and social complexity in chimpanzees

Two sets of experiments are described, testing the ability of chimpanzees to recognise states of mind in others. These are part of a larger series of experiments involving chimp-chimp and chimp-human interactions. In one experiment, a chimpanzee was familiarised to a baseline condition in which they indicated to a helper whichever of two containers had been baited with food whilst the helper had been absent. The helper shared the food with the chimpanzee. A key was required to open the box and was always hung in the same place. In probe trials, the helper put food in one of the boxes, but was absent when the key was removed by a third party and hidden. In these trials, the chimpanzee first directed the attention of the helper to the position of the key rather than a box. This chimpanzee thus appeared sensitive to states of ignorance versus knowledge in the helper. In a second experiment, chimpanzees showed sensitivity to the attentional focus of a human interactant, in a variety of behavioural manifestations. I argue that these abilities imply recognition of the conditions corresponding to ‘states of mind’. Such abilities may be adaptations for dealing with complexities of chimpanzee social life, but in turn create more socially complex agents.

B. Open Session

E.J. Stokes & R.W. Byrne (School of Psychology, University of St Andrews)

Coping with injury: feeding skills and adaptations of the chimpanzees of Budongo Forest, Uganda.

Although gorillas and orang-utans have been shown to display considerable skill in order to obtain some plant foods, this has not been described in chimpanzees except in the restricted context of tool use. Furthermore, in the Sonso community of chimpanzees at Budongo Forest in Uganda, over 20% of individuals suffer from some form of upper or lower limb injury as a result of snares. This study focused on the feeding technique of able-bodied chimpanzees and the manner of compensation in the case of injury. Data were collected from September 1997 until September 1998, based on 22 able-bodied and 8 injured individuals. For one food type examined, able bodied individuals show considerable standardization in their feeding with a preference for two techniques (technique defined as a regularly used sequential organization of individual actions). Injured chimpanzees show a reduction in use of one of these preferred techniques. The nature and extent of injury determines the degree of difference from the able-bodied population. Rather than invent novel techniques, injured individuals compensate by modifying their existing repertoire to work around their impairments. As a result, only the most severe of injuries results in a decline in feeding efficiency.

Joanne Martin (Biology and Environmental Studies, Bolton Institute)

Does Human Rearing and Mother Separation Effect the Behaviour of Captive Chimpanzees?

Chimpanzees (Pan troglodytes) that are kept in captivity come from a wide variety of backgrounds, such as laboratory and circus animals, performers and pets. This study investigated the long-term effect that removing from their mother and/or other chimpanzees has on chimpanzees behaviour. The aim was to provide an insight into the social development of the species and to investigate human influence on this process. Chimpanzees were studied at six zoos in the United Kingdom. It was predicted that, regardless of the environment, captive chimpanzees with a ‘deprived’ background would show behavioural differences, specifically that their social skills would not show the complexity of ‘normal’ chimpanzees. Results indicated that if differences exist between ‘normal’ and ‘socially deprived’ individuals then ‘deprived’ individuals showed lower levels of activity, poorer social skills and higher levels of abnormal behaviour. It was also found that environmental effects influence their behaviour suggesting that the zoo environment may go some way to reduce the influence of a deprived background. These results have implications for the welfare and management of this species in captivity.

Kathryn Hill (Department of Biological Sciences, University of Liverpool)

An observation of meat eating in captive orangutans.

During a period of observation of captive orangutans at Chester Zoological Gardens, a wild rabbit, which had accidentally strayed into the study area, was captured, killed and eaten. Although the capture and killing of birds by orangutans has been witnessed before by researchers and zoo staff, carnivorous behaviour had never been reported, and was in this case carried out by a new male member of the group. Although this incident was possibly nothing more than a spontaneous reaction to a novel occurrence, it is an interesting addition to reports of meat eating by wild orangutans.

Clea Assersohn & Andrew Whiten (Department of Psychology, University of St. Andrews)

Food sharing between mother and infant chimpanzees in the wild: beggars can be choosers.

By comparison with tool use and meat eating, basic foraging behaviour in chimpanzees has been under-studied, and we know little of its developed. We therefore studied eight infants of the Sonso community of chimpanzees (Pan troglodytes schweinfurthii) in Budungo Forest Uganda, and compared their foraging to the more competent patterns of their mothers and five sibling juveniles. Alternate observations on these mothers and offspring were made over a twelve-month period using the focal sampling method. Characteristic and common to chimpanzee’s early foraging experiences is the sharing of food between mother and infant on which this paper focuses. These food transfers provide a clear opportunity for social learning, and so it is possible to that they play an important role in the development of an infant’s feeding ability. It was found that mothers transferred food most frequently to their infants when they were in their first and second year. Infants solicited particularly those foods they found difficult to procure or process (p < 0.05), obtaining food from their mothers at different stages of processing. Hence results show that infants’ are refined in their attempts to gain experience with particular food items. The relationship between degree of food transfer and subsequent foraging success is a measure of the importance of these events in an infant’s progression to independent foraging.

Mark J. Prescott & Hannah M. Buchanan-Smith (Department of Psychology, University of Stirling)

Foraging efficiency in single- and mixed-species troops of tamarins.

To date there is little empirical field evidence for the hypothesis that, through participation in mixed-species troops, individual primates may increase their foraging efficiency. A series of experiments, using artificially provisioned trees, investigated whether the presence of a congener facilitates foraging behaviour and how this might lead to increased foraging efficiency in mixed-species troops. Single-species troops of free-ranging Saguinus fuscicollis and S. labiatus were found to discriminate between feeding sites of varying profitability and to distribute their search effort accordingly. Subsequent testing was performed with mixed-species troops, with each species possessing divergent (i.e. correct and incorrect) knowledge about site profitability. Naïve (those with incorrect knowledge) individuals attended to the behaviour of their knowledgeable congenerics and followed them to productive patches. However, it was found that the subordinate S. fuscicollis did not benefit from the opportunity to observe and interact with knowledgeable S. labiatus who aggressively defended and monopolized the most productive sites. Dominant S. labiatus, however, benefited through association with knowledgeable S. fuscicollis. This study highlights individual and species asymmetries in costs and benefits of mixed-species troop formation.

R.A. Hill (School of Biological Sciences, University of Liverpool)

It ain’t half hot mum! Behavioural responses of baboons to the thermal environment.

Traditionally, studies of primate ecology have tended to focus on the importance of food availability, since access to sufficient food resources is a primary factor limiting reproductive success. As a consequence, the importance of the thermal environment as a constraint upon primate behavioural ecology has received relatively little attention. Despite this, a number of studies have suggested thermoregulation as an important ecological force. This study examined the importance of the thermal environment on activity scheduling by baboons (Papio cynocephalus ursinus) at De Hoop Nature Reserve, South Africa. Both diurnal and seasonal patterns in resting, grooming and combined non-foraging activity were consistent with the need to perform more sedentary activities as temperatures increased. Logistic regression analysis revealed that the ‘perceived environmental temperature’ was a significant determinant of whether the baboons would be engaged in non-foraging activities, and subsequent analyses revealed that this was due to the high occurrence of these activities when ‘environmental’ temperatures exceeded the baboons thermal neutral zone. Furthermore, due to the high dependence of environmental temperatures on the intensity of solar radiation, the thermal environment was also significantly correlated with time spent in shade, with the baboons spending proportionally more time in shade when temperatures exceeded their thermal neutral zone. The thermal environment is thus an important ecological constraint upon baboon activity scheduling decisions. This indicates that non-foraging activities may not simply represent a reserve of time that can be drawn upon to satisfy additional feeding requirements. Rather, under certain conditions, baboons may be constrained to non-foraging activities in order to maintain a net thermoregulatory balance.

Mary Strate (School of Biological Sciences, Nicholson Building, University of Liverpool)

The Communication Network of the Gelada Baboon, Theropithecus gelada

Species living in complex societies often maintain a ‘social network’ of affiliates, yet it is not well understood how animals maintain these bonds. Dunbar (1991, 1993) posits that vocalisations are a less costly alternative to traditional grooming, in terms of time budgets, but how vocalisations are interdigitated with other affiliative behaviours has never been examined in depth. It is possible that social factors, such as group size and harem membership, impose constraints on affiliative behaviours which make one affiliative behaviour ‘inexpensive’ in particular ecological contexts.

Gelada baboons live in complex multi-tiered societies, and it is possible that the social network between harem units is more effectively managed through communication. All harems have been studied using focal animal sampling of both intra-harem and inter-harem relationships to better understand how traditional grooming and vocal grooming function to reinforce cohesion between and within harems. Acoustic analyses of gelada vocal exchanges have revealed temporal and sequential patterns which suggest that contact calling behaviours also track the ‘rules’ of social relationships.

Dunbar, R.I.M. (1991) Functional significance of social grooming in primates. Folia Primatologica 57:121-131.

Dunbar, R.I.M. (1993) Coevolution of neocortical size, group size and language in humans. Behavioral and Brain Sciences. 16: 681-735.

Tom Sambrook (Department of Psychology, University of Stirling) & Mark Taylor (Department of Astronomy, University of Cambridge)

Data For Free: How to estimate association between non-focal subjects

Studies of social complexity often use focal sampling of a restricted set of focal animals to achieve adequate resolution of behavioural detail. Restricting sampling to a few focal animals precludes analyses of whole-group social structure (e.g. of cliquing) which are not only of interest in their own right but may serve to inform, in a top-down manner, discussion of the fine behaviour of individuals that the restricted-focal method is designed to illuminate.

We show how the pattern of association of non-focal animals with a focal can be used mathematically to infer these non-focal’s true association, producing an estimate that is compatible with standard measures and allowing, in principle, the construction of a matrix of associations for all group members. We discuss differences between association based on dyadic vs. polyadic decision making by animals.

Sarah Elton (Department of Biological Anthropology, University of Cambridge)

Habitat at southern African Plio-Pleistocene palaeontological sites, as suggested by ecomorphological analysis of taxonomically unassigned cercopithecoid postcranial elements.

The locomotor strategy and habitat preference of extinct primates can be inferred from their postcranial skeletons. In this work, fossil cercopithecoid postcranial elements from southern African Plio-Pleistocene palaeontological sites have been examined using ecomorphological analysis. This is a useful technique in palaeontology because the habitat of a fossil organism can be inferred directly from its skeletal features rather than relying on assumptions based on closely-related modern species, and, as such, can be used on even taxonomically unassigned material.

The comparative sample used in this analysis comprised 215 extant Old World monkeys from twelve genera selected to show a wide range of locomotor strategies and habitat preferences. Measurements taken on the postcrania of these specimens were regressed against body mass, and the measurements that were not highly correlated with body mass were converted into dimensionless ratios. The comparative sample was divided into four habitat groups (forest terrestrial, forest arboreal, open terrestrial and open mixed) and Discriminant Function Analysis (DFA), a multivariate statistical technique used to assign variables to the most-probable classification category, was used to distinguish between them.

Fossil specimens studied came from Swartkrans Members 1 and 2, Sterkfontein Member 4, Makapansgat Member 4, Kromdaai A and B, and Bolt’s Farm. All were taxonomically unassigned, and as such ideal for inclusion in ecomorphic analysis. The DFA of the humerus assigned over 60% of the fossil sample to the open mixed category, and the rest to the open terrestrial category, suggesting an open/mosaic habitat at these sites. These results are consistent with other work on the palaeoecology of southern African Plio-Pleistocene palaeontological sites.

S. Caless (Biology & Environmental Studies, Bolton Institute)

Seasonal variations of aggression in two species of lemur (Lemur catta and Eulemur fulvus rufus).

Initial observations of captive and wild Lemur catta and Eulemur fulvus rufus were undertaken to test hypotheses on intersexual and interspecific aggression. Previous research indicates that L. catta show female dominance and E. f. rufus do not. This research focuses on the levels and types of aggression emitted by these two lemur species. It was predicted that L. catta females would show higher levels of aggression towards males than E. f. rufus females, but that levels and types of female aggression in both species would vary seasonally. It was also predicted that this pattern would reflect the underlying, metabolically stressful periods of reproduction in the female. Findings indicate these predictions were generally supported, with differences being seen both between and within the two species. The relationship between these differences and the social and hierarchical organisation of these species is discussed, with reference to how the differences in aggressive behaviours may correspond to the male role within the species.