Group-living Primates Research Articles

Roadside Dining: The Collective Movement Behavior of Sulawesi Moor Macaques in a Provisioning Context.

How group-living primates come to a consensus about navigating their environment is a result of their decision-making processes. Although decision-making has been examined in several primate taxa, it remains underexplored for primates living in anthropogenic landscapes. To shed light on consensus decision-making and flexibility in this process, we examined collective movement behavior in a group of wild moor macaques (Macaca maura) experiencing a risk-reward tradeoff as a result of roadside provisioning within Bantimurung Bulusaraung National Park in South Sulawesi, Indonesia. Our goal was to determine whether individual characteristics (e.g., sex, dominance rank, and/or social network centrality) predict the likelihood of initiating a collective movement and if the opportunity to receive food provisions along the road alters these patterns. Using the all-occurrences method, we recorded the location, time, and identity of initiators and followers of each collective movement observed from April to June 2023 (N = 61). We used conditional logistic regression models to examine which individual characteristics predicted initiation overall and based on two destination categories: forest- and road-directed collective movements. Initiation was distributed amongst most of the group, indicating a partially-shared decision-making style. Overall, adult males were more likely to initiate collective movements than adult females. However, for collective movements directed toward the risky roadside, dominance, rather than sex, was a better predictor of initiation, with higher ranked individuals being more likely to initiate collective movements. Examining the decision-making processes in this species through collective movements can provide insight into how primates come to a consensus and the extent to which anthropogenic factors shape these processes. By shedding light on how moor macaques navigate the risk-reward tradeoff at this site, our results can also inform the management of human-macaque interfaces.

And Baby Makes Three: Postpartum Changes in Male-Female Affiliative Interactions in White-Faced Capuchins.

In group-living primates, male investment in infants is highly variable. Previous research on polygynandrous primates found that male care of infants, whether direct or indirect, may be a means to increase offspring survival, increase social status, invest in future mating opportunities, and/or invest in future social or coalition partners, any of which may increase fitness outcomes. Relationships between male white-faced capuchins (Cebus imitator) and infants are highly variable, ranging from neutral to highly affiliative during periods of group stability to lethal during times of instability. We used genetic paternity analysis and behavioral observations to investigate the impact of paternity status, female dominance rank, male dominance rank, and infant sex on changes in rates of affiliation (contact and proximity) between capuchin males and females following the birth of an infant (n = 92 dyads). We used generalized linear mixed models and an information theory approach to select models for averaging. We found that overall rates of male-female affiliation increased following the birth of an infant (contact change: +1.09 ± 2.55%; proximity change: +1.16 ± 3.08%). Infant sex was the only significant explanatory variable; dyads that included males and females who gave birth to male infants experienced a significant increase in their time in contact and proximity in comparison to dyads with females who gave birth to female infants (contact change: p < 0.05 in 2/3 models; proximity change: p < 0.001 in 3/3 models). These findings add to previous data indicating that male capuchins do not recognize their offspring or have the motivation to preferentially invest in their care. We suggest that the observed sex bias may be a form of sex-specific socialization connected to the importance of forming long-term cooperative male bonds that are maintained via male parallel dispersal in this species.

Social ageing can protect against infectious disease in a group-living primate.

The benefits of social living are well established, but sociality also comes with costs, including infectious disease risk. This cost-benefit ratio of sociality is expected to change across individuals' lifespans, which may drive changes in social behaviour with age. To explore this idea, we combine data from a group-living primate for which social ageing has been described with epidemiological models to show that having lower social connectedness when older can protect against the costs of a hypothetical, directly transmitted endemic pathogen. Assuming no age differences in epidemiological characteristics (susceptibility to, severity and duration of infection), older individuals suffered lower infection costs, which was explained largely because they were less connected in their social networks than younger individuals. This benefit of 'social ageing' depended on epidemiological characteristics and was greatest when infection severity increased with age. When infection duration increased with age, social ageing was beneficial only when pathogen transmissibility was low. Older individuals benefited most from having a lower frequency of interactions (strength) and network embeddedness (closeness) and benefited less from having fewer social partners (degree). Our study provides a first examination of the epidemiology of social ageing, demonstrating the potential for pathogens to influence the evolutionary dynamics of social ageing in natural populations.This article is part of the discussion meeting issue 'Understanding age and society using natural populations'.

Social ageing can protect against infectious disease in a group-living primate.

The benefits of social living are well established, but sociality also comes with costs, including infectious disease risk. This cost-benefit ratio of sociality is expected to change across individuals' lifespans, which may drive changes in social behaviour with age. To explore this idea, we combine data from a group-living primate for which social ageing has been described with epidemiological models to show that having lower social connectedness when older can protect against the costs of a hypothetical, directly transmitted endemic pathogen. Assuming no age differences in epidemiological characteristics (susceptibility to, severity, and duration of infection), older individuals suffered lower infection costs, which was explained largely because they were less connected in their social networks than younger individuals. This benefit of 'social ageing' depended on epidemiological characteristics and was greatest when infection severity increased with age. When infection duration increased with age, social ageing was beneficial only when pathogen transmissibility was low. Older individuals benefited most from having a lower frequency of interactions (strength) and network embeddedness (closeness) and benefited less from having fewer social partners (degree). Our study provides a first examination of the epidemiology of social ageing, demonstrating the potential for pathogens to influence evolutionary dynamics of social ageing in natural populations.

Edge effects and social behavior in three platyrrhines.

Social behavior is a key adaptation for group-living primates. It is important to assess changes to social behavior in human-impacted landscape zones to better understand the impact of anthropogenic disturbance on primate species. We investigated social behavior rate and type in three species of platyrrhines across 100 m anthropogenic edge and interior zones of a fragmented forest in Costa Rica, La Suerte Biological Research Station (LSBRS). Following results from other sites, we predicted that spider monkeys (Ateles geoffroyi), capuchin monkeys (Cebus imitator) and howler monkeys (Alouatta palliata) would show lower rates and fewer types of social behavior in forest edge compared to interior. We collected 1341 h of instantaneous focal data from 2017 to 2023 across the three monkey species. We found mixed support for our predictions, with spider and capuchin monkeys modifying some but not all aspects of social behavior across forest zones at LSBRS. Spider monkeys had lower rates of social behavior and capuchin monkeys performed different types of social behaviors in forest edge compared to interior at LSBRS. In contrast, howler monkeys did not modify social behavior. Two out of three platyrrhine species altered their social behavior when in anthropogenic edges, indicating behavioral adjustment when in human-altered habitat areas at LSBRS.

Vigilance has mainly a social function in a wild group of spider monkeys (Ateles geoffroyi).

Vigilance is a widespread behavior that allows individuals to socially acquire information and/or effectively detect potential risks posed by predators and conspecifics. In this study, we aimed to investigate how social factors (i.e., subgroup size, number of males and immatures in the subgroup, presence of fission and fusion events, subgroup activity), individual characteristics (i.e., sex, presence of dependent offspring) and possible vulnerability to predation (i.e., being in smaller subgroups or lower in the canopy) explain variation in vigilance behavior in a wild group of spider monkeys (Ateles geoffroyi). We collected vigilance data during focal samples of all adults, subadults and juveniles of the group (N = 38), and ran generalized linear mixed models with a Bayesian approach. We found that the proportion of time both sexes spent in vigilance increased with subgroup size and during fusion events. Individuals also spent more time in vigilance when the subgroup was resting or socializing compared to other activities. Moreover, the proportion of time spent in vigilance increased in subgroups with more immatures. An alternative model with similar fit suggested that the proportion of time spent in vigilance increased in females when subgroups included more adult and subadult males. Overall, these results suggest that our study group mainly directed vigilance toward conspecifics (i.e., social vigilance), probably as a result of the relatively low predation pressure experienced, and contribute to the understanding of the multiple social factors affecting vigilance in group-living primates.

Social network inheritance and differentiation in wild baboons.

Immatures' social development may be fundamental to understand important biological processes, such as social information transmission through groups, that can vary with age and sex. Our aim was to determine how social networks change with age and differ between sexes in wild immature baboons, group-living primates that readily learn socially. Our results show that immature baboons inherited their mothers' networks and differentiated from them as they aged, increasing their association with partners of similar age and the same sex. Males were less bonded to their matriline and became more peripheral with age compared to females. Our results may pave the way to further studies testing a new hypothetical framework: in female-philopatric societies, social information transmission may be constrained at the matrilineal level by age- and sex-driven social clustering.

Reduced injury risk links sociality to survival in a group-living primate

Sociality has been linked to a longer lifespan in many mammals, including humans. Yet, how sociality results in survival benefits remains unclear. Using 10 years of data and over 1,000 recorded injuries in rhesus macaques (Macaca mulatta), we tested two injury-related mechanisms by which social status and affiliative partners might influence survival. Injuries increased individual risk of death by 3-fold in this dataset. We found that sociality can affect individuals' survival by reducing their risk of injury but had no effect on the probability of injured individuals dying. Both males and females of high social status (measured as female matrilineal rank and male group tenure) and females with more affiliative partners (estimated using the number of female relatives) experienced fewer injuries and thus were less likely to die. Collectively, our results offer rare insights into one mechanism that can mediate the well-known benefits of sociality on an individual's fitness.

Dominance or Tolerance? Causes and consequences of a period of increased intercommunity encounters among bonobos (Pan paniscus) at LuiKotale

Group-living primates exhibit variable reactions to intergroup encounters (or IGEs), reflecting species-specific strategies and individual motivations. In chimpanzees (Pan troglodytes), dominating in IGEs provides fitness benefits. Less is known about responses to IGEs in bonobos (Pan paniscus) despite their equal relevance for understanding the origins of human intergroup relations. We observed the Bompusa West (WBp) bonobo community at LuiKotale during a 2-month shift in ranging resulting in frequent IGEs with the smaller Bompusa East (EBp) community. We tested whether incursions provided ecological benefits, and whether responses to IGEs were consistent with inter-community dominance or tolerance. We measured fruit availability and collected activity scans from 26 mature WBp community members when in their core ranging area, during incursions into the EBp ranging area, and during IGEs. We collected data on sexual interactions and aggression with in-group and out-group members during 19 independent IGEs. During their shift in ranging, fruit availability was greater in the EBp ranging area, and WBp bonobos consumed more fruit during incursions than when in their core ranging area. Coalitionary intergroup aggression occurred during nine IGEs, and outcomes were consistent with imbalances in fighting power, in that larger WBp parties supplanted smaller EBp parties from the immediate area. However, communities reformed associations following 70% of coalitionary conflicts, and prolonged IGEs facilitated out-group sexual interactions and female transfers. The WBp community shift in ranging was likely motivated by ecological factors and responses to increased IGEs reflected a mixture of competitive and tolerant strategies.

Mothers stick together: how the death of an infant affects female social relationships in a group of wild bonobos (Pan paniscus)

Sociality is widespread among group-living primates and is beneficial in many ways. Sociality amongst female bonobos (Pan paniscus) has been proposed to have evolved as a female counterstrategy to male infanticide and sexual coercion. In male-philopatric bonobo societies, females mostly form relationships with unrelated females. Among these social relationships, it has been proposed that females with infants (also referred to as mothers) tend to have strong relationships with each other (mother-bonding hypothesis). In this paper, we use the case of an infant death in a group of wild bonobos in the Kokolopori Bonobo Reserve, Democratic Republic of Congo, to test this hypothesis. By using dyadic sociality indices for grooming, proximity, and aggression, we investigated whether the infant death influenced dyadic relationships the mother had with other group members. Before the infant death, grooming index (GI) and proximity index (PI) scores were the highest between the focal mother and another mother. After the death, the relationship of this mother dyad weakened, as indicated by lower GI and PI scores, whereas the relationship of another mother dyad became stronger. Aggression index scores among the mothers were comparable before and after the death, suggesting that changes in mother affiliative relationships were not a by-product of changes in overall interaction frequencies. Also, PI scores increased between the focal mother and three non-mothers after the death. Collectively, the shift in social dynamics between the focal mother and other group members after the infant death partially supported the mother-bonding hypothesis.

Evaluating adaptive hypotheses for female-led infanticide in wild chimpanzees

Although rare among group-living primates, infanticide by females has been reported in several chimpanzee, Pan troglodytes, populations. We examined 13 infanticidal attacks over 47 years at Gombe National Park, Tanzania to evaluate three adaptive hypotheses. (1) Exploitation of the infant as a food resource – by eating a vulnerable neonate, attackers gain calories that may be important during periods of food scarcity or energetic stress. (2) Resource competition – Gombe females concentrate their foraging in overlapping core areas and dominance rank influences foraging success. By killing the infant of a female with high core area overlap, the perpetrator removes a current and future competitor, improving her access to food. (3) Low cost – female chimpanzees mature and reproduce slowly, and longevity increases reproductive success. Physical aggression causes risk of severe injury or death, so females will only mount attacks when risks to the perpetrator are low. In support of hypothesis 1, females usually consumed the carcass. However, attacks were not more likely in times of resource or energy scarcity. In support of hypothesis 2, females attacked others with whom they shared core areas, but attacks did not cause shifts in ranging patterns. In support of hypothesis 3, one or more attackers always outranked the victim, the attacks often involved coalitions and victims usually lacked kin support. Attacks were more likely to be successful when attackers were not hindered by clinging infants and victims could not retreat. Our results provide further evidence for female competition and the adaptive value of female-led infanticide in this species.

Japanese macaques relax vigilance when surrounded by kin

Vigilance behaviour in group-living animals helps to detect threats. Individual vigilance levels are thought to decrease as group size or the number of neighbours increases. However, the results of studies on the effects of group size or the number of neighbours are inconsistent, especially in primates. Since social vigilance (i.e. monitoring for group members) plays an essential role in group-living primates, discrepancies among studies may have been caused by differences in the quality of social relationships between group members. Using data from a provisioned group of Japanese macaques, Macaca fuscata , this study examined the effects of the quality of social relationships and the number of neighbours on vigilance levels. We found that the frequency of vigilance was lower when the majority of an individual's neighbours were kin than when kin were in the minority. Since Japanese macaques show strong nepotism and cope with social threats by forming coalitions between close kin, individuals may be able to reduce their vigilance levels by relying on the vigilance of potential allies. Furthermore, when the majority of neighbours were kin, the proportion of time spent on vigilance decreased as the number of neighbours increased. However, when kin were in the minority of neighbours, the number of neighbours did not affect vigilance levels. Overall, our results indicate that the quality of social relationships with neighbours and the number of neighbours interactively affect vigilance levels. • Several social factors affect individual vigilance levels in Japanese macaques. • Time spent vigilant decreased as the number of neighbours increased. • This effect of the number of neighbours exists only if the neighbours are kin. • Vigilance levels may be adjusted depending on the quality of social relationships.

Effects of Female Group Size on the Number of Males in Blue Monkey (Cercopithecus mitis) Groups

The number of males per group varies substantially in group-living primates, both between and within species. In blue monkeys (Cercopithecus mitis), males may temporarily join groups during annual mating seasons when sexually receptive females are present. A likely determinant of the number of males per group is female group size (the number of adult females in a group). To clarify the role of female group size in driving variation in the number of males per group, we expanded on earlier observations of a wild population in the Kakamega Forest, Kenya with a larger sample of groups that varied fivefold in female group size. We found considerable flexibility in social organization, with groups experiencing multimale episodes both during and outside mating seasons, some persisting over multiyear periods. The dichotomy between single- and multimale mating seasons was less distinct than previously reported, suggesting greater variation in multimale states. Across 65 group-specific conception periods, female group size strongly influenced how often multiple sexually active females and multiple males were present in a group. The number of sexually active females present on a given day related closely to the number of males in the group that same day, especially during conception periods. Results suggest that males join and remain in larger groups where mating opportunities are greater and costs of joining or staying may be lower than in smaller groups. This longitudinal study highlights intraspecific social variation within and across groups while confirming that female group size influences the number of males.

Deconstructing sociality: the types of social connections that predict longevity in a group-living primate.

Many species use social interactions to cope with challenges in their environment and a growing number of studies show that individuals which are well-connected to their group have higher fitness than socially isolated individuals. However, there are many ways to be 'well-connected' and it is unclear which aspects of sociality drive fitness benefits. Being well-connected can be conceptualized in four main ways: individuals can be socially integrated by engaging in a high rate of social behaviour or having many partners; they can have strong and stable connections to favoured partners; they can indirectly connect to the broader group structure; or directly engage in a high rate of beneficial behaviours, such as grooming. In this study, we use survival models and long-term data in adult female rhesus macaques (Macaca mulatta) to compare the fitness outcomes of multiple measures of social connectedness. Females that maintained strong connections to favoured partners had the highest relative survival probability, as did females well-integrated owing to forming many weak connections. We found no survival benefits to being structurally well-connected or engaging in high rates of grooming. Being well-connected to favoured partners could provide fitness benefits by, for example, increasing the efficacy of coordinated or mutualistic behaviours.

Maternal protectiveness is negatively associated with infant handling in wild Japanese macaques

Abstract Infant handling by a non-mother is common in many primate species. Despite the requirement of a triadic relationship among handler, mother, and infant, previous studies of infant handling have focused on characteristics of handler or interactions between mother and handler. In this study, we examined the influence of the mother–infant relationship (i.e., maternal style) on the frequency with which wild Japanese macaque (Macaca fuscata) infants were handled. We analysed behavioural data collected during 3 consecutive years and found that maternal style was characterised by three principal components: infant activity, rejection, and non-protectiveness. Infants who were less active and whose mothers were less protective received more frequent handling. These effects were particularly evident when handlers were thought to have less access to the infant. These complex interactions within the triadic relationship suggest that maternal style constrains the occurrence of infant handling in group-living primates.

The presence of females induces elevated cortisol levels in an alpha male: Experimental evidence in chimpanzees.

In group-living primates, it has been reported that the alpha male exhibits high concentrations of cortisol and testosterone in the context of mating competition. We investigated how the presence of females affected salivary cortisol and testosterone levels in males from a small captive group of chimpanzees (Pan troglodytes). Specifically, we assessed whether the presence of females resulted in a rapid increase in salivary cortisol and testosterone levels in the alpha male. We compared the social behavior and salivary hormone concentrations of four males before and after the presentation of receptive females. Three times a day, we collected saliva samples, a useful matrix for investigating short-term hormonal changes, and measured cortisol and testosterone concentration by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The frequency of inter-male aggression increased in the presence of females, indicating intense competition among males. Salivary cortisol levels increased in all males in the presence of females; however, the increase was significantly more pronounced in the alpha male. We found a complex three-way interaction among the presence of females, sampling timings, and male dominance rank in the analysis of salivary testosterone. Contrary to our prediction, a post hoc analysis revealed that salivary testosterone levels decreased after female introduction and that the alpha male did not show a higher level of salivary testosterone. Our study provides experimental evidence suggesting that the presence of females plays a significant role in the rank-related variation in the cortisol levels in male chimpanzees. Furthermore, our findings demonstrate the usefulness of salivary hormones for detecting short-term physiological changes in studies of socioendocrinology.

Reevaluating cases of trait-dependent diversification in primates.

Previous investigations have identified several ecological traits that may have shaped differences in species richness among primate clades by influencing speciation and extinction probabilities. In this study, I reevaluate these cases in light of concerns about high false-positive rates of the methods used to detect trait-dependent diversification. Data for six traits were taken from the literature: activity pattern, sociality, mating system, terrestriality, frugivory, and mutualistic interactions with angiosperms (i.e., seed dispersal and pollination). These traits were treated as binary variables and analyzed in a phylogenetic framework using likelihood-based and nonparametric methods for estimating trait-specific diversification rates. Of the traits analyzed here, only activity pattern was found by all methods to be correlated with diversification: diurnal primates diversify at higher rates than nocturnal primates. Solitary foragers have a lower rate of diversification than group-living primates, but this link is driven by the association between solitariness and nocturnality. These results indicate that ecological traits have had a more limited influence on primate diversification than suggested by previous studies. The false positives detected here can be linked with heterogeneity in diversification caused by sources other than the focal traits. One of these sources is the very high rate of diversification in Cercopithecoidea found in previous investigations. Another is the correlation between activity patterns and diversification. The underlying causal mechanism for the contrast in diversification dynamics between diurnal and nocturnal primates is unclear, but this correlation highlights the important role of activity pattern in shaping primate evolutionary history.

Male dominance relationships in an extremely large chimpanzee community at Ngogo, Kibale National Park, Uganda

Abstract Male dominance hierarchies occur in many group-living primates and some non-primate mammals. Variation in aspects of agonistic relationships such as how many dyads show bidirectionality in aggression leads to variation in dominance hierarchies along a continuum from egalitarian (relatively small agonistic power differences between adjacently-ranked individuals, shallow hierarchies) to despotic (relatively large differences, steep hierarchies). Ranks usually depend mostly or entirely on individual characteristics that influence fighting ability (e.g., body size) and show inverse-U shaped relationships to age. However, coalitionary support sometimes also influences ranks. Chimpanzees (Pan troglodytes) form multi-male, multi-female communities within which males compete for status. Males typically form dominance hierarchies, and data from multiple study show that rank is positively related to paternity success. Males also often form coalitions and some dyads form long-term alliances. Effective coalitionary support can help individuals improve and maintain their ranks, and some evidence supports the hypothesis that coalitionary aggression generally, and the positions that males hold in coalitions networks specifically, influences paternity success. Hierarchy steepness varies among communities and within communities over time; variation in the number of prime-aged males per community is a likely source of this variation. Long-term data from an extremely large chimpanzee community with unusually many males, at Ngogo, Kibale National Park, Uganda, are largely consistent with previous analyses of male chimpanzee dominance hierarchies, but show several notable contrasts. Males at Ngogo formed significantly linear hierarchies and hierarchy steepness was greater than expected if the outcomes of agonistic interactions were random. However, variation in steepness did not show the significant inverse relationship to the number of “prime-aged” males documented for other chimpanzee communities and average steepness was high given the large number of males. Ranks showed an inverse-U shaped relationship to age, although individual rank trajectories varied considerably, but males attained their highest lifetime ranks at later ages and maintained relatively high ranks to later ages than those at other chimpanzee research sites. Two measures of coalition networks, strength and Bonacich power, showed significant positive relationships with male ranks. Strength is the rate at which males joined coalitions. Bonacich power is a measure of network centrality that assesses a male’s relational power, or influence (Bonacich, 1987): a male with high Bonacich power formed coalitions with relatively many other males who were also central in the coalition network, i.e., he was strongly connected to powerful others. On average, males also attained maximum values for these and other network measures relatively late and maintained relatively high values to relatively late ages. High coalition network strength, Bonacich power, and eigenvector centrality early in adulthood were associated with high peak ranks at later ages. However, the direction of causality between participation in coalition networks and ranks is not yet clear, and the effects of body size on dominance ranks and individual rank trajectories remains to be explored. Ngogo is a favourable habitat for chimpanzees and survivorship there is unusually high; this presumably facilitates the ability of males to maintain high competitive ability longer than at other sites and shifts rank trajectories toward older ages and leads to relatively steep hierarchies despite the fact that many male dyads have similar competitive ability. Future work will assess the impact of coalitions on dominance relationships in more detail and the relationship of coalitionary aggression to paternity success.

Long-term analysis on the variance of extra-group paternities in rhesus macaques

Extra-group paternity (EGP) has been described in various mammalian species; however, little is known about which factors contribute to the variation in EGP, as the majority of studies were restricted in time and the number of groups considered. Using longitudinal demographic and genetic data, we aim to investigate which factors predict rates of EGP in the free-ranging rhesus macaque population of Cayo Santiago, Puerto Rico (USA). Of the 1649 infants considered which were born into six social groups over 9 years, we identified an average of 16% of infants resulting from EGPs. We tested the influence of group size, breeding group sex ratio, female reproductive synchrony, and group instability on the occurrence of EGPs. Our results suggest a tendency for EGPs to increase as the proportion of females increased in larger groups, but no such effect in smaller groups. Furthermore, as group instability and female reproductive synchrony decreased, the number of EGPs tended to increase. Our results support the hypothesis that group structure affects the occurrence of EGPs, which might be mediated by male mating opportunities, male monopolization potential, and/or female choice.Significance statementIn several species, both sexes seek alternative reproductive strategies to enhance their reproductive success. For instance, females may pursue EGPs to potentially increase genetic compatibility with males, or males may seek EGPs to improve their mating opportunities. Our longitudinal analysis, including demographic and genetic data over 9 years of six social groups of rhesus macaques, revealed high variation in the occurrence of EGPs across groups and years, and this variation tended to depend on group characteristics such as breeding group size, sex ratio, female synchrony, and group instability. The data suggest that group structure affects the number of EGPs in this group-living primate. Our results show that EGPs can affect the distribution of paternity within social groups and should be taken into account when assessing reproductive success.

How Many for Lunch Today? Seasonal Fission-Fusion Dynamics as a Feeding Strategy in Wild Red-Capped Mangabeys (Cercocebus torquatus)

For group-living primates, social organization hinges upon multiple factors, including group size, group cohesion, and the group's age and sex composition. Fission-fusion dynamics reduce the risks of living in a large group, which can include feeding competition related to the seasonality of resources. Here we report on the group dynamics (i.e. formation of parties) of a population of red-capped mangabeys (Cercocebus torquatus) located in Sentier Nature forest, South Loango National Park, Gabon, and examine the role of fruit availability in episodes of fission-fusion and shifting range use during the peak fruiting season of 2014. To assess fission-fusion dynamics, we obtained data on party type (i.e. number, size and age-sex composition), the effect of availability of fruit from 4 tree species on the home range and habitat used by parties, and the periodicity of these processes. The results show that red-capped mangabeys displayed seasonal fission-fusion dynamics related to fruit availability during the season under study.