Post-conflict Behaviour of Wild Olive Baboons. II. Stress and Self-directed Behaviour

Previous studies indicate that the proximate function of post-conflict affiliative interaction among primates is to reduce a victim's uncertainty about its opponent's future behaviour: the ‘uncertainty reduction hypothesis’ (Aureli & van Schaik 1991; Ethology, 89 , 101–114). This study confirms and extends these results, demonstrating that they are neither a product of captivity nor specific to macaques: both victims and initiators of aggression in a large group of wild olive baboons exhibited elevated rates of self-directed behaviour (SDB) - scratching, autogrooming, body-shaking and yawning - in a 10-min post-conflict period. During this period, they were more likely to receive further aggression. Reconciliation reduced both SDB and the incidence of further aggression. However, reconciliation only reduced SDB among individuals involved in conflicts in which both parties exchanged aggression. It is suggested that aggressors in unilateral conflicts were aroused rather than uncertain and that their victims' lack of control over post-conflict interactions (which tended to be initiated by their opponents) prevented them from benefiting from reconciliation in the same fashion as longtailed macaque victims, which frequently initiated reconciliation.     

Post-conflict Social Events in Wild Mountain Gorillas. II. Redirection,Side Direction,and Consolation

Inevitably, members of primate groups sometimes have aggressive contests with each other. Targets of aggression can engage in several types of interaction with third parties to ameliorate its adverse effects. They can redirect aggression, which may reduce the risk of further aggression from the initial opponents and reduce tension, or they can initiate affinitive interactions with third parties, in order to seek protection or reassurance. They can also receive reassuring acts from them (‘consolation’). Researchers have documented high levels of redirection in many primate species, but consolation is thus far known only in chimpanzees. Data on post-conflict social interactions between targets of aggression and third parties in two groups of wild mountain gorillas (Gorilla gorilla beringei) show that immatures and subordinate males, but not females, redirect aggression at high rates. Furthermore, immatures seek affinitive interactions with their mothers, and adult females seek them with adult males, at elevated rates. Affinitive interactions between females and males seem mainly to have a protective function and are associated with decreased risks of further aggression between female opponents. Redirection by females after female-female conflicts may be uncommon because targets commonly retaliate against aggressors. Males may offer females protection and consolation as services, and the results support the argument that such services are important when dominance relationships between females are often undecided and retaliation between opponents is common.     

Wild Female Olive Baboons Adapt their Grunt Vocalizations to Environmental Conditions

Sound propagates differently and visibility varies according to the habitat type. Animals should therefore adapt the acoustic structure and the usage of their vocal signals to the environment. In the present study, we examined the influence of the habitat on the vocal behaviour of wild olive baboons ( Papio hamadryas anubis ) in two populations: one living in Gashaka-Gumti National Park, Nigeria, and the other in Budongo Forest, Uganda. We investigated whether female baboons modified the acoustic structure of their grunts and their rate of grunting when they wandered between closed and open habitat types. As an adaptation to the environmental conditions, baboons might utter calls with a longer duration, a lower fundamental frequency and/or energy concentrated in lower frequencies in a closed habitat like forest than in an open habitat. Baboons should also grunt more frequently in the closed habitat. Analyses showed that in both populations grunts uttered in forest were significantly longer than in open habitat. Additionally, baboons from Uganda showed a significantly higher grunt rate in forest than in open habitat. These results revealed a certain degree of plasticity in vocal production and call usage with regard to the habitat type. However, results in Nigeria suggested that, besides habitat structure, other proximate factors like the context of calling and the proximity between group members could also have an influence on the actual communication patterns.     

Reconciliation and Consolation in Captive Western Gorillas

We studied post-aggression mechanisms in a captive group of western gorillas (Apenheul Primate Park, The Netherlands) and compared them with those of wild mountain gorillas (Gorilla beringei). We found the same trend for reconciliation that wild mountain gorillas show: reconciliation occurred only between adult male-female dyads, while it was absent in the other sex-age class combination. There were both solicited and nonsolicited contacts; the latter finding is in contrast with the result obtained in wild mountain gorillas, in which consolation was absent. Immature females were more likely to offer consolation toward both related and unrelated individuals. Consolation did not reduce the likelihood of further attacks among group members. It may be that, as the α-male plays a fundamental role in preventing the spread of conflicts throughout the entire group, triadic contacts become ineffective for the function. The levels of consolation were higher in absence of reconciliation than in its presence, suggesting that consolation may function as an alternative mechanism in stress reduction of the victim.     

Post-conflict Social Events in Wild Mountain Gorillas (Mammalia,Hominoidea). I. Social Interactions between Opponents

Researchers have documented elevated rates of affinitive interaction between opponents shortly after aggressive conflicts, or reconciliation, in many primate species. Reconciliation may ameliorate the immediate negative effects of aggression by reducing the chance of further aggression between opponents and thus reducing tension, and may avert or repair damage to long-term social relationships important to the animals' fitness. Data on post-conflict interactions between opponents in two groups of wild mountain gorillas (Gorilla gorilla beringei) fail to show reconciliation after conflicts between females, between males, or between immatures, but females seem to commonly reconcile themselves with males after receipt of male aggression. Females and subordinate males often avoid same-sex opponents after conflicts. Females commonly retaliate against female aggressors, and post-conflict rates of aggression between females are higher than baseline levels. Females may not need to achieve reconciliation with each other because relationships between co-resident relatives are resiliant, while those between non-relatives are mostly neutral to antagonistic. Males are, however, important social partners and protectors of females, and female transfer is common. Thus, the results strongly support the ‘important relationships’ hypothesis for the function of reconciliation.     

Testicular Size,Mating System,and Maturation Schedules in Wild Anubis and Hamadryas Baboons

We report body mass and testicular size in 258 anubis (Papio anubis or P. hamadryas anubis) and 59 hamadryas (P. hamadryas or P. h. hamadryas) baboons, live-trapped in Ethiopia. As predicted by theories of sexual selection by sperm competition, among hamadryas baboons, which are monandrous, fully adult males have absolutely and relatively smaller testes than those of comparable males among anubis baboons, which are polyandrous. Male hamadryas are also ca. 10% smaller in bodily mass as adults. The intertaxonal difference in adults is due entirely to the fact that in male anubis baboons, testicular and bodily mass continue to grow up to full adulthood–the age at which most males emigrate from their natal troop and initiate a confrontational breeding strategy among unrelated animals. By contrast, male hamadryas baboons, which are usually philopatric, attain adult body mass and testicular size as subadults. In both species, juveniles experience rapid testicular growth peaking in rate at ca. 12kg body mass, but testicular descent and growth starts earlier in hamadryas than in anubis baboons. Juvenile hamadryas baboons have relatively larger testes than their anubis equivalents, perhaps because male philopatry allows the mating strategy of male hamadryas baboons to be initiated during juvenile life and therefore permits some sperm competition between juveniles and adults.     

Canine Length in Wild Male Baboons: Maturation,Aging and Social Dominance Rank

Canines represent an essential component of the dentition for any heterodont mammal. In primates, like many other mammals, canines are frequently used as weapons. Hence, tooth size and wear may have significant implications for fighting ability, and consequently for social dominance rank, reproductive success, and fitness. We evaluated sources of variance in canine growth and length in a well-studied wild primate population because of the potential importance of canines for male reproductive success in many primates. Specifically, we measured maxillary canine length in 80 wild male baboons (aged 5.04–20.45 years) from the Amboseli ecosystem in southern Kenya, and examined its relationship with maturation, age, and social dominance rank. In our analysis of maturation, we compared food-enhanced baboons (those that fed part time at a refuse pit associated with a tourist lodge) with wild-feeding males, and found that food-enhanced males achieved long canines earlier than wild-feeding males. Among adult males, canine length decreased with age because of tooth wear. We found some evidence that, after controlling for age, longer canines were associated with higher adult dominance rank (accounting for 9% of the variance in rank), but only among relatively high-ranking males. This result supports the idea that social rank, and thus reproductive success and fitness, may depend in part on fighting ability mediated by canine size.     

High Prevalence of Simian T-Lymphotropic Virus Type L in Wild Ethiopian Baboons

Simian T-cell leukemia viruses (STLVs) are the simian counterparts of human T-cell leukemia viruses (HTLVs). A novel, divergent type of STLV (STLV-L) from captive baboons was reported in 1994, but its natural prevalence remained unclear. We investigated the prevalence of STLV-L in 519 blood samples from wild-living nonhuman primates in Ethiopia. Seropositive monkeys having cross-reactive antibodies against HTLV were found among 22 out of 40 hamadryas baboons, 8 of 96 anubis baboons, 24 of 50 baboons that are hybrids between hamadryas and anubis baboons, and 41 of 177 grivet monkeys, but not in 156 gelada baboons. A Western blotting assay showed that sera obtained from seropositive hamadryas and hybrid baboons exhibited STLV-L-like reactivity. A PCR assay successfully amplified STLV sequences, which were subsequently sequenced and confirmed as being closely related to STLV-L. Surprisingly, further PCR showed that nearly half of the hamadryas (20 out of 40) and hybrid (19 out of 50) baboons had STLV-L DNA sequences. In contrast, most of the seropositive anubis baboons and grivet monkeys carried typical STLV-1 but not STLV-L. These observations demonstrate that STLV-L naturally prevails among hamadryas and hybrid baboons at significantly high rates. STLV-1 and -2, the close relative of STLV-L, are believed to have jumped across simian-human barriers, which resulted in widespread infection of HTLV-1 and -2. Further studies are required to know if STLV-L is spreading into human populations.     

Baboons, chimpanzees, and tools

Wild chimpanzees make and use tools with far greater frequency and variety than wild baboons. Sampling differences; differences in the sensory, motor, or cognitive capacities for skilled tool use; or environmental differences are not responsible. Fortuitous discovery of novel forms of tool behavior probably occurs as rarely among chimpanzees as among baboons. However, research on wild and captive chimpanzees reveals that the discovery is transmitted quickly among chimpanzee groups by observation learning, and thus becomes well-established in the group's behavioral repertoire. In contrast, study of captive baboons reveals that they acquire little information about tool behavior by observation. With little observation learning the behavior is not likely to be acquired by other group members since repeated independent discovery is improbable. Thus chimpanzees' more proficient tool behavior is due mainly to their greater capacity for observation learning. This suggests that the advent of hominid tool traditions was accompanied by a capacity for facile observation learning and thus, perhaps, by language ability.     

Reproductive Characters and Mating Behaviour of Wild Nomascus hainanus

We report for the first time the reproductive behaviors of Hainan gibbons (Nomascus hainanus), based on 29 mo of field observations. Receptive females initiated courtship displays. Copulatory patterns involved the male mounting dorsoventrally from above and behind. Multiple intromissions with thrusting were brief, lasting <10 s per copulation. We observed multiple copulations ≤4 times/d, but could not confirm multiple ejaculations. We also observed postconception proceptivity and copulations in sexually active females. We estimated the gestation period to be 136–173 d. Infants became independent at 1.5 yr, and the natal group could drive out maturing offspring at ca. 5.5 yr. The interbirth interval is ca. 24 mo. Our limited data also suggest that mating activities peak in the rainy season. The Hainan gibbons are polygynous, with a 1 male-2 females mating system. We hypothesize that suboptimal habitat quality and limited forest area may contribute to the current mating structure, but more work needs to be done over a longer period to understand better the sociosexual behaviors of this critically endangered species.     

Correlates of Self-Directed Behaviour in Wild White-Faced Capuchins

Elevated rates of self‐directed behaviour (SDB) such as self‐scratching and autogrooming have been widely used in recent years as an indicator of anxiety in catarrhine primates. This study presents the first examination of correlates of SDB rates in a platyrrhine primate. Subjects were 8 wild female white‐faced capuchins at Lomas Barbudal, Costa Rica, who were observed for 119 h of focal individual follows. The subjects performed significantly more self‐scratching and autogrooming while in close proximity to conspecifics than while alone, irrespective of whether the neighbour was dominant or subordinate to them. This result was attributable to elevated SDB rates during the 30 s preceding and following allogrooming bouts. Furthermore, subjects engaged in more SDB while in proximity to females (a) that were closer to them in dominance rank and (b) with whom they spent a larger proportion of their time in proximity. Self‐directed behaviour rates after conflicts did not differ from non‐postconflict rates. Nor were SDB rates above baseline levels during the 30 s before subjects descended to the ground. These results may provide support for the view that SDB rates index anxiety in this species, if grooming decisions signal individuals' current allegiances and are therefore a source of anxiety, even if being groomed is, itself, relaxing. Postconflict preparation for further aggression may mitigate against scratching and autogrooming in a fast‐moving arboreal species.     

Point of Care Blood Gas and Electrolyte Analysis in Anesthetized Olive Baboons (Papio anubis) in a Field Setting

International Journal of Primatology - Biotelemetry requires animal captures to deploy collars. Capture raises ethical concerns, as field chemical immobilizations are complex procedures, during...     

Ontogenetic Scaling of Fore- and Hind Limb Posture in Wild Chacma Baboons (Papio hamadryas ursinus)

Large-scale interspecific studies of mammals ranging between 0.04–280 kg have shown that larger animals walk with more extended limb joints. Within a taxon or clade, however, the relationship between body size and joint posture is less straightforward. Factors that may affect the lack of congruence between broad and narrow phylogenetic analyses of limb kinematics include limited sampling of (1) ranges of body size, and/or (2) numbers of individuals. Unfortunately, both issues are inherent in laboratory-based or zoo locomotion research. In this study, we examined the relationship between body mass and elbow and knee joint angles (our proxies of fore- and hind limb posture, respectively) in a cross-sectional ontogenetic sample of wild chacma baboons (Papio hamadryas ursinus) habituated in the De Hoop Nature Reserve, South Africa. Videos were obtained from 33 individuals of known age (12 to ≥108 months) and body mass (2–29.5 kg) during walking trials. Results show that older, heavier baboons walk with significantly more extended knee joints but not elbow joints. This pattern is consistent when examining only males, but not within the female sample. Heavier, older baboons also display significantly less variation in their hind limb posture compared to lighter, young animals. Thus, within this ontogenetic sample of a single primate species spanning an order of magnitude in body mass, hind limb posture exhibited a postural scaling phenomenon while the forelimbs did not. These findings may further help explain 1) why younger mammals (including baboons) tend to have relatively stronger bones than adults, and 2) why humeri appear relatively weaker than femora (in at least baboons). Finally, this study demonstrates how field-acquired kinematics can help answer fundamental biomechanical questions usually addressed only in animal gait laboratories.     

Postconflict Behavior of Spectacled Leaf Monkeys (Trachypithecus obscurus). I. Reconciliation

Studies of postconflict behavior have focused on Old World primates, particularly on members of the cercopithecines and chimpanzees. We present data on patterns of reconciliation in two captive groups of spectacled leaf monkeys, members of the Colobinae. Reconciliation occurred at a high rate relative to that in other primate species and within the first minute following a conflict. Friendly postconflict contact was usually initiated by aggressors in one group, and by recipients in the other. But, there was no difference in postconflict initiative to contact in comparison with MCs. These two groups showed behavioral specificity in the context of postconflict reunions. Ventroventral embracing was a common, explicit (de Waal, 1993) form of reconciliation. The intensity of aggression and situations in which the victim responded aggressively had no effect on the likelihood of reconciliation occurring. The postconflict behavior of both groups lends further support to the relationship-quality hypothesis (Aureli et al., 1989). Kinship and rank distance and had no effect on reconciliation, though affiliation levels correlated positively with the tendency to reconcile. These results indicate that spectacled langurs are among the more tolerant of the species studied so far.     

A Statistical Modelling Approach to the Occurrence and Timing of Reconciliation in Wild Japanese Macaques

In various social species, animals have been observed to share friendly relationships with some group members and to resolve conflicts through reconciliation, the exchange of affiliative behaviour soon after a conflict that functions to restore the relationship between the former opponents. The valuable relationship hypothesis predicts that reconciliation should be observed more often after conflicts between friends. Friendly relationships can be described by three dimensions (i.e. value, security and compatibility); however, research into the relative importance of these dimensions for the occurrence of reconciliation is sparse. Moreover, reconciliation may depend on factors other than the social relationship between opponents including, for example, their social status or the context of the conflict. Our study aimed at analysing which factors are important determinants of reconciliation and at testing the valuable relationship hypothesis, by analysing the relative effects of relationship value, security and compatibility on the occurrence and timing of reconciliation. We collected data on two troops of wild Japanese macaques living on Yakushima Island, Japan, and selected the best predicting variables of reconciliation using linear mixed models. Our results show that reconciliation occurs more frequently, and earlier, after conflicts between opponents who exchange a higher percentage of grooming. Two additional variables related to relationship security and value were selected in the best models: frequency of aggression and of approaches resulting in tolerated co‐feeding. Among the variables not related to relationship quality, distance between opponents at the end of the conflict, kinship, sex of the opponents and context of conflict (i.e. during feeding or social time) were included in our models. Our findings support the valuable relationship hypothesis and, in particular, highlight that the fitness‐related benefits of social relationships (i.e. the relationship value) are important determinants of the evolution of friendly relationships and reconciliation.     

Collective Behaviour without Collective Order in Wild Swarms of Midges

Collective behaviour is a widespread phenomenon in biology, cutting through a huge span of scales, from cell colonies up to bird flocks and fish schools. The most prominent trait of collective behaviour is the emergence of global order: individuals synchronize their states, giving the stunning impression that the group behaves as one. In many biological systems, though, it is unclear whether global order is present. A paradigmatic case is that of insect swarms, whose erratic movements seem to suggest that group formation is a mere epiphenomenon of the independent interaction of each individual with an external landmark. In these cases, whether or not the group behaves truly collectively is debated. Here, we experimentally study swarms of midges in the field and measure how much the change of direction of one midge affects that of other individuals. We discover that, despite the lack of collective order, swarms display very strong correlations, totally incompatible with models of non-interacting particles. We find that correlation increases sharply with the swarm''s density, indicating that the interaction between midges is based on a metric perception mechanism. By means of numerical simulations we demonstrate that such growing correlation is typical of a system close to an ordering transition. Our findings suggest that correlation, rather than order, is the true hallmark of collective behaviour in biological systems.