The role of kinship in the formation of a primate multilevel society

A small number of mammalian species live in a modular or multilevel society in which several individual social/reproductive units called one-male units (OMUs) are embedded within a large cohesive band. Factors that affect band composition and stability are poorly understood. In this study we examined the role of kinship in the formation and maintenance of a multilevel society in an endangered population of golden snub-nosed monkeys (Rhinopithecus roxellana). From 2005 to 2011, we obtained genetic samples from 86 individuals (including 88.9% of leader males and 80.5% of adult females) living in a band of 8–10 OMUs. We used microsatellite genotyping to identify patterns of relatedness and individual transfer. We found that adult females residing in the same OMU were more closely related to each other than to a random set of females drawn from the band and that females tended to disperse into OMUs that contained female relatives. In addition, adult females who transferred were not more closely related to their previous leader male than to the leader male of their new OMU. These results support the contention that kin bonds contribute importantly to the formation and stability of this primate multilevel society by influencing a female's decision to remain in her current OMU, or during transfer, which new OMU to enter. Am J Phys Anthropol 156:606–613, 2015. © 2014 Wiley Periodicals, Inc.     

Female social dynamics in a provisioned free-ranging band of the Sichuan snub-nosed monkey (Rhinopithecus roxellana) in the Qinling Mountains, China

Little information is available on the social dynamics of the Sichuan snub-nosed monkeys (Rhinopithecus roxellana). Here, we provide 5-year observational data on a provisioned free-ranging band in the Qinling Mountains, central China, from October 2001 to December 2005. The results of this study suggested that females place a high priority on maintaining long-term relationships with other female in their one-male units (OMUs). Females had more social interactions with unit members than with nonunit individuals. They showed relatively high rates of affiliation with their unit females, intermediate levels with the resident males, and low levels with individuals outside the unit. Females had few interactions with other resident males. Social interactions, especially affiliative interactions, were more symmetrical between focal females and their unit females than between focal females and the resident males. Thus female social interactions appeared to resemble those of other female-bonded primate societies. On the other hand, female transfers occurred sometimes. We recorded 11 cases of female immigration and 5 cases of female disappearance, 1 case of female intraband shift, and 2 cases of "merging of OMUs," which suggested that unit females might be loose-knit in this species. We discussed influencing factors on female Sichuan snub-nosed monkey social dynamics, by comparing them with those of Hamadryas and gelada baboons that also have multilevel societies.     

Comparisons of Intraunit Relationships in Nonhuman Primates Living in Multilevel Social Systems

Multilevel social systems have evolved in several species of cercopithecoid primates and appear to be an effective means of changing group size amid variation in environmental conditions. Larger groupings of these species fission and fuse, making intraunit relationships essential to maintain the integrity of the smallest social units. We examine these intraunit relationships in four primates with multilevel social systems: proboscis monkeys (Nasalis larvatus), snub-nosed monkeys (Rhinopithecus roxellana), hamadryas baboons (Papio hamadryas), and geladas (Theropithecus gelada), using social network analysis. The proboscis monkeys and hamadryas baboons were wild and unprovisioned, whereas the snub-nosed monkeys and geladas were partly provisioned. Comparison of eigenvector centrality coefficients revealed a phylogenetic difference in the key individuals maintaining social networks between the colobines and the cercopithecines: females were more central in proboscis and snub-nosed monkeys, with males generally peripheral to social interaction, whereas males were more central than females in geladas and hamadryas. A comparison of sex differences in clustering coefficients, however, revealed a significant difference only in geladas, suggesting that one-male–multifemale units in this species become more unstable when females, but not males, are removed from social networks. Taken together, our results reveal the strongest differences between geladas, characterized by female philopatry and male dispersal, and the three species with bisexual dispersal. These results demonstrate the potential for social network analysis to reveal the social bonds most important for maintaining cohesion of the smallest units of primate multilevel societies. This, in turn, can serve as a proxy, in the absence of long-term data, for underlying patterns of sex-biased dispersal and philopatry.     

Social organization of black-and-white snub-nosed monkeys (Rhinopithecus bieti) at Deqin, China

Data on social organization of two bands of black-and-white snub-nosed monkeys (Rhinopithecus bieti) were collected when the monkeys were crossing an open spot at Nanren and Bamei (northwest of Yunnan, China) using a sampling rule where individuals within one social unit are spatially closer to each other than individuals between social units. The typical pattern of social organization in this sample was multiple adult females (AFs) and their offspring with one adult male (AM) in a one-male unit (OMU), similar to that of many other colobines. In such units, on average one male is associated with 4.0 AFs and 2.5 of their offspring. Moreover, there are multimale/multifemale units and monogamous units besides OMUs. All bisexual units traveled together with at least one all-male unit as a cohesive band. In two bands of monkeys, 87% of AMs in bisexual units were within OMUs, 7.8% within monogamous units and 5.2% within multimale, multifemale units. In the Bamei band, 6.7% of AMs were in the all-male unit. The size of OMUs in the Nanren band was larger than that of the Bamei band, with more AFs and juveniles, which may be related to better conservation in the Nanren band's habitat. For the Nanren band, the average number of AFs in OMUs varied across time, increasing from 4.3 in 1994 to 5.1 in 2001, and then decreasing to 3.8 in 2005. This article suggests three possible explanations for this variation, but more data are needed for these hypotheses to be tested.     

Dominance relationships among one-male units in a provisioned free-ranging band of the Sichuan snub-nosed monkeys (Rhinopithecus roxellana) in the Qinling Mountains, China

We studied the dominance relationships among one-male units (OMUs) in a provisioned free-ranging band of the Sichuan snub-nosed monkeys (Rhinopithecus roxellana) in the Qinling Mountains of central China from 2001 to 2005. The band was composed of 6-8 OMUs that stayed in the band for several years. Linear dominance orders could be detected using displacement interactions with directional asymmetry among OMUs in 82.3+/-5% of interactions, and ambiguous and reversed interactions in 17.7+/-5%. The dominance rank of OMUs was positively related with the duration of their stay in the band, and this may be attributed to the association of the resident male with adult females, rather than the fighting ability of resident males, as males do not fight seriously with each other. Subordinate units were observed to merge with dominant units resulting in an elevation of their rank order. The linear dominance relationship among OMUs in the Sichuan snub-nosed monkeys may have evolved as a result of competition for preferred food trees.     

Social functions of relaxed open-mouth display in golden snub-nosed monkeys(Rhinopithecus roxellana)

Relaxed open-mouth display serves important social functions in relation to submission, reconciliation affiliation and reassurance among non-human primate societies; however, quantitative evidence on this behavior remains insufficient among multi-level social groups. From July to November 2016, we examined four potential functions of the relaxed open-mouth display during pairwise, intra-unit social interactions among 18 free-ranging adult and sub-adult golden snub-nosed monkeys(Rhinopithecus roxellana) who belonged to three one-male, multi-female units(OMU) at Dalongtan, Shennongjia National Park China. Results showed that: compared with no relaxed open-mouth display,(1) the occurrence of displacement by a dominant individual approaching a subordinate was lower and the distance of the subordinate to the approaching dominant was shorter when the subordinate showed open-mouth display;(2) relaxed open-mouth display reduced the probability of continued attack for victims of aggression and allowed victims to achieve closer proximity to the aggressor during post-conflict periods;(3) relaxed open-mouth display by dominant individuals allowed them to achieve closer proximity to subordinates; and(4) the exchange of relaxed open-mouth display had a greater impact on the outcome of interactions than one individual alone giving this signal. These findings suggest that relaxed open-mouth display serves important functions regarding submission, reconciliation, affiliation and reassurance in coordinating social interactions within OMUs in golden snub-nosed monkeys.     

Female choice impacts resident male takeover in golden snub-nosed monkeys(Rhinopithecus roxellana)

In primate species with social systems consisting of one-male breeding units(OMUs), resident male takeover represents a major challenge to individual reproductive success and mating strategies. The golden snub-nosed monkey(Rhinopithecus roxellana)is characterized by large multilevel societies(MLS)comprised of several OMUs and all-male units(AMUs);however, the factors and mechanisms associated with resident male takeover, which offer important insight into primate reproduction and social strategies, are still poorly understood. Based on 5-year monitoring data from a free-ranging herd of golden monkeys from the Qinling Mountains in China, we categorized three phases of an OMU, that is, a rising phase,developing phase, and declining phase. The rising and declining phases were unstable periods in which male takeover in an OMU might occur. Factors causing takeover, such as leader male rank, fighting ability, reproduction rate, and affiliation(proximity,allogrooming), were analyzed for males and females and for different OMUs. Results indicated that the new resident male's fighting ability was lower than that of the former resident male in 23 cases. After replacement, the rank order of the new resident male significantly declined. Females involved in a takeover increased their distance from the resident male and decreased mating frequency during the three months prior to takeover. Females with infants under one-year-old had a marked effect on the specific time of takeover occurrence. These results suggested that female choice was the main factor deciding whether a takeover attempt was successful. Furthermore, rather than male conflict, females more often initiated and affected takeover and outcome, implying that the social status and competitive ability of the males played lesser roles during takeover.     

Social dynamics of the golden snub‐nosed monkey (Rhinopithecus roxellana): female transfer and one‐male unit succession

Among primates that form multilevel societies, understanding factors and mechanisms associated with the movement of individuals between groups, clans, and one‐male social units offers important insight into primate reproductive and social strategies. In this research we present data based on an 8‐year field study of a multilevel troop of Sichuan snub‐nosed monkeys (Rhinopithecus roxellana) in the Qinling Mountains of China. Our study troop contained 78–126 individuals, and was usually organized into 6–8 one‐male units (OMU). The majority of OMUs were composed of networks of unrelated females and their offspring. We found that 59.7% (43/72) of subadult and adult females in our study troop transferred between OMUs (n=66) or disappeared (n=7) from the troop. In the majority of cases, two or more females transferred together into new OMUs or troops. In R. roxellana, new OMUs formed in several ways. During 2001–2008, 16 adult males appeared in the study troop. Over this period, we observed 13 different males who became harem leaders either by taking over an existing harem or by attracting females from other OMUs into their harem. We also observed four OMUs from a neighboring troop to successfully immigrate into the study troop. The number of individuals in these newly immigrated OMUs was significantly smaller than that number of individuals in resident OMUs. During harem formation, fighting between adult males was rarely observed, and female mate choice appeared to play a crucial role in harem male recruitment and replacement. These results suggest that golden snub‐nosed monkeys are organized in a nonmatrilineal social system. Female mate choice and possibly incest avoidance appear to play important roles in female transfer, male tenure, and OMU stability. Am. J. Primatol. 71:670–679, 2009. © 2009 Wiley‐Liss, Inc.     

雄性川金丝猴对雌性的受孕认知与等级识别

社会认知是群居动物适应复杂环境和社会生活能力的体现,致力于理解自身、他人与社会。认知有利于促进利益分配的优化,而行为认知策略则是关注的热点问题。但迄今为止,川金丝猴如何进行社会地位与受孕状态等基础认知尚不清楚。本研究通过投食招引,在个体识别和等级判定的基础上,以栖息于秦岭观音山自然保护区熊猫谷景区的一个半野生川金丝猴群为对象,采用瞬时扫描和焦点动物取样法,观察并收集了猴群中6个一雄多雌单元成年雌雄个体的空间位置、邀配、交配及产仔行为数据,结合食物密度梯度"同心圆"和受孕周期,推测雌性成功受孕的交配时间段,运用配对t-检验统计证实受孕前后雌性的交配实现率差异显著(t=4.527,P=0.001),表现为受孕前雌性邀配行为获取的雄性响应率明显高于受孕后;通过Spearman相关性检验发现,雌性受孕前的交配实现率(R=0.527,P=0.006)及受孕时间(R=0.556,P=0.049)与自身等级均显著正相关,即高等级雌性邀配行为的雄性响应率及与雄性生殖性交配的时间明显高于或早于低等级雌性。结果表明,雄性川金丝猴拥有认知单元内成年雌性受孕状况和等级地位的能力,这种认知能力影响着雄性的性行为方式。     

Spatiotemporal association patterns in a supergroup of Rwenzori black-and-white colobus (Colobus angolensis ruwenzorii) are consistent with a multilevel society

Primates display broad diversity in their social organization. The social groups of a few primate species are organized in a multilevel fashion, with large groups composed of multiple, core one-male units (OMUs). A characteristic of multilevel societies is that the higher levels can include hundreds of individuals. The Rwenzori black-and-white colobus (Colobus angolensis ruwenzorii) in the montane forests of Rwanda form supergroups and have been suspected to exhibit multilevel social organization. Here we present the first data on the “anatomy” of a supergroup numbering 500+ individuals. We identified subgroups within the supergroup based on progression data, extracting the social network structure from the time-stamped spatiotemporal distribution of passing individuals identified to age–sex class, and selecting an optimal time window for each network using the two-step approach developed by Uddin, Choudhury, Farhad, and Rahman (2017). We detail the existence of core units—multi-male units (MMUs) with a mean of 1.7 adult males and 3.1 adult females, as well as OMUs, all-female units and bachelor units composed of adult and sub-adult males. More than two-thirds of units are MMUs. These grouping patterns conform to a multilevel society with predominantly multi-male core units, a social system that has recently also been described for a population of the same taxon in Uganda. Individual identification will be required to corroborate these interpretations.     

中国云南塔城滇金丝猴的社会结构

在云南塔城附近的山地森林中,我们利用摄象机记录了一群滇金丝猴通过山谷和在水源地饮水的过程。我们利用这些记录分析这群滇金丝猴的种群大小、组成成员以及个体的空间分布,并利用连续通过个体之间的时间间隔来揭示社会结构。塔城滇金丝猴群由366个个体组成,是目前所知最大的滇金丝猴群体。猴群内雌性个体较多。猴群可以分为26个单位,其中有19个单雄多雌单位、5个多雄多雌单位和2个全雄单位。统计结果表明单位内个体间的时间间隔显著比单位间的短。2/3以上的亚成年雄性个体和全雄单位一起活动。猴群在地面活动时全雄单位位于猴群的外围,充当前卫和后卫。塔城猴群的生命表组成结构与吾牙普亚猴群的大致一样,同样是多层社会结构,单雄多雌和全雄单位构成猴群的主体。亚成年雄性多数与全雄单位一起活动,表明雄性可能会从其出生的单雄多雌单位中迁移出来。     

Female preferences for male golden snub-nosed monkeys vary with male age and social context

Age is a key factor affecting sexual selection, as many physical and social traits are age-related. Although studies of primate mate choice often consider particular age-related traits, few consider the collective effects of male age. We tested the hypothesis that female golden snub-nosed monkeys Rhinopithecus roxellana prefer prime aged males (10–15 years) over younger and older males. We examined a habituated, provisioned troop during a 3-year study in the Qinling Mountains, China. Prime age males were more likely to be resident males of 1-male units (OMUs) than males of other ages. Since females are free to transfer between OMUs, the number of females per OMU can be indicative of female preferences. We examined the number of females per OMU, and found that it increased with resident male age up to 7–8 years, and declined after 12 years, such that prime age resident males had more females than other resident males. Females also initiated extra-unit copulations with high-ranking prime age males at significantly higher rates than with other males. Nevertheless, females tended to transfer from OMUs with high-ranking, older resident males to those with low-ranking, younger resident males. Thus, females appear to use different strategies when choosing social mates and extra-unit mates (i.e., different social contexts). We speculate that females may perceive early signs of aging in males and trade off the benefits and costs of high rank versus male senescence. This study lays the groundwork for future studies that examine possible direct and indirect benefits of such strategies.     

A study on the social structure and dispersal patterns of hamadryas baboons living in a commensal group at Taif,Saudi Arabia

Three levels of hamadryas social structure—the one male unit (OMU), the band, and the troop—have been observed at all sites studied, but a fourth—the clan—has been observed at only one site, Erer-Gota, Ethiopia, during a longitudinal check of the dispersion of identified individuals. The clan is important since it appears to provide the basis for male philopatry, although comparative data is needed from other sites to confirm this. We studied a huge commensal group of hamadryas baboons (over 600 animals) in Saudi Arabia. We put ear tags on baboons between 1998 and 2004 and analyzed social structure, relying on the interactions of these tagged animals by focusing especially on their dispersal patterns from OMUs. OMU membership tended to be looser than that of the Ethiopian hamadryas. Females tended to shift between OMUs on an individual basis in our study group, whereas the collapse of an OMU was a major occasion of adult female transfer in Ethiopia. We found neither stable bands (a “band” in our study group was defined as a regional assemblage of OMUs) nor clans that lasted for several years. Some OMUs moved and transferred into neighboring areas over both the short and long term. Further, some post-adolescent males appeared to move out of the study area. The ratio of adult females in an OMU in our study group was larger than for any other documented study site, and this may be the reason for enhanced female transfer between OMUs. A large proportion of the adolescent females showed no clear membership to OMUs, and no “initial units” (commonly observed in Ethiopia) were discernible. The ease with which young males acquired adult females at the study site must have disrupted the formation of a clan, a “male-bonded society.”     

Impact of male takeover on intra-unit sexual interactions and subsequent interbirth interval in wild Rhinopithecus roxellana

Data were collected on sexual interactions before and after a male takeover of a one-male unit (OMU) of Sichuan snub-nosed monkeys (Rhinopithecus roxellana) in the Qinling Mountains, China. The original unit consisted of an adult male, 2 adult and 2 subadult females, 2 female juveniles and a single infant. Following the takeover, the new resident male copulated with 1 adult female, which was not lactating. Subsequent to the disappearance of her infant, the second (lactating female) entered breeding condition and began to solicit copulation with the new resident male. The subadult females also engaged in matings with the new male. The new resident male was observed mating, on 3 occasions, with females in 2 other OMUs. These are the first observations of sexual behaviour in free-ranging Sichuan snub-nosed monkeys after an OMU takeover. Sexual interactions play an important role in establishing relationships between the new male and resident females in the OMU.     

Sexual interference in the Golden snub-nosed monkey (Rhinopithecus roxellana): a test of the sexual competition hypothesis in a polygynous species

Sexual interference (SI), which is defined as any disturbance directed to a mating pair by other individuals, has been reported in several primate species. It is widely suggested that successful harassers experience improved mating success by increasing their access to reproductive partners as well as by reducing the mating success of rivals. Although theories of primate sexual conflict highlight male intra-sexual mating competition, females also are reported to actively disrupt copulations between mating partners. In this study, we investigated SI in a multilevel troop of Golden snub-nosed monkeys (Rhinopithecus roxellana) inhabiting the Qinling Mountains, China. Behavioral observations of 11 one-male units (OMU) that comprised the multilevel troop were conducted from September 2007 to May 2008. During this period 17.1% of 652 documented intra-OMU sexual encounters were characterized either by mild or aggressive forms of harassment. Sexual harassment was typically performed by a single individual (91.9%), and in 75.7% of cases the harasser was an adult or sub-adult female. The frequency of female harassment was positively correlated with the number of adult and sub-adult females residing in an OMU, and resulted in a significant decrease in matings ending in ejaculation. We found that the amount of SI a female received was not a significant predictor of her reproductive success. However, females who conceived during the mating season directed higher levels of harassment at other females than females who did not conceive. We evaluate the strength of the sexual competition hypothesis and the hormonally modulated aggression hypothesis in explaining patterns of SI in female Golden snub-nosed monkeys.     

Multilevel Societies in New World Primates? Flexibility May Characterize the Organization of Peruvian Red Uakaris (Cacajao calvus ucayalii)

Researchers have described multilevel societies with one-male, multifemale units (OMUs) forming within a larger group in several catarrhine species, but not in platyrhines. OMUs in multilevel societies are associated with extremely large group sizes, often with >100 individuals, and the only platyrhine genus that forms groups of this size is Cacajao. We review available evidence for multilevel organization and the formation of OMUs in groups of Cacajao, and test predictions for the frequency distribution patterns of male–male and male–female interindividual distances within groups of red-faced uakaris (Cacajao calvus ucayalii), comparing year-round data with those collected at the peak of the breeding season, when group cohesion may be more pronounced. Groups of Cacajao fission and fuse, forming subgroup sizes at frequencies consistent with an OMU organization. In Cacajao calvus ucayalii and Cacajao calvus calvus, bachelor groups are also observed, a characteristic of several catarrhine species that form OMUs. However, researchers have observed both multimale–multifemale groups and groups with a single male and multiple females in Cacajao calvus. The frequency distributions of interindividual distances for male–male and male–female dyads are consistent with an OMU-based organization, but alternative interpretations of these data are possible. The distribution of interindividual distances collected during the peak breeding season differed from those collected year-round, indicating seasonal changes in the spatial organization of Cacajao calvus ucayalii. We suggest a high degree of flexibility may characterize the social organization of Cacajao calvus ucayalii, which may form OMUs under certain conditions. Further studies with identifiable individuals, thus far not possible in Cacajao, are required to confirm the social organization.     

Proximity association in polygynous western black crested gibbons (Nomascus concolor jingdongensis): network structure and seasonality

We investigated the structure and seasonality of the proximity network in a group of polygynous western black crested gibbons (Nomascus concolor) using social network analysis. The spatial proximity changed seasonally and was affected by temperature and rainfall. Preferred proximity association was not distributed randomly among individuals. Kinship was one explanation for the social structure, as offspring preferred to maintain close proximity with their mothers. The proximity of infants to mothers decreased with age, and independent offspring had lower proximity to mothers than dependent ones. We found that the adult male had different proximity relationships with two different adult females. The frequency of proximity between the male and the infant-carrying female was significantly higher than that between the male and the female who had immigrated carrying one offspring of uncertain paternity into the group. Infanticide avoidance and/or predation protection for dependent infants might explain the proximity relationship differences. Temperature influenced group proximity association, with individual proximity increasing in the cold months and decreasing in the hot months. Group proximity decreased in months with higher anthropogenic disturbance.     

Social System of a Hybrid Baboon Group (Papio anubis × P. hamadryas)

We describe the social organization, mating system, and social structure of a group of hybrid baboons (Papio anubis×P. hamadryas) in Ethiopia's Awash National Park. The group contained elements of both hamadryas and anubis societies. Overall, the group was a multimale, multifemale group that lacked cohesion and frequently formed subgroups. Subgroup formation was more strongly associated with predation risk than food availability. Although there were several hamadryas-like one-male units OMUs within the group, there was no evidence of a hamadryas multilevel society. Male and female members of OMUs were phenotypically more hamadryas-like than non-OMU individuals. The group contained substantial variation in the strength of inter- and intrasexual bonds: some females primarily groomed males while other females primarily groomed females, and the patterns were consistent with the OMU substructure. Despite some promiscuous mating, mating was biased towards the hamadryas condition for all group members. Additionally, rates of immigration and emigration were very low, and mean pairwise relatedness within the group is rising. For measures of intersexual bonding, all members of the group were intermediate between anubis and hamadryas individuals in less hybridized groups. The group was phenotypically and behaviorally more intermediate than it was in the 1970s (Sugawara, K. (1988). Primates 29: 429–448.) and the changes may indicate a relatively young and dynamic hybrid zone.     

A preliminary study on the function of food begging in Sichuan snub-nosed monkeys (Rhinopithecus roxellana): challenge to begging for nutritional gain

Several hypotheses have been developed to explain what benefits a donor may gain from sharing food with another individual, with nutritional gain assumed to be the sole benefit for the beggar. Recently, it has been proposed that begging behaviour serves a social function in non-human primates. In this study, the nutritional-gain assumption was again challenged based on observations on a captive group of Sichuan snub-nosed monkeys (Rhinopithecus roxellana), or golden snub-nosed monkeys. The major findings from this study are that (1) beggars sometimes left their own branches or passed by available branches to beg for similar food from other individuals, (2) beggars occasionally ignored branches that were acquired by begging and (3) food begging occurred more frequently in the all-male unit after the social rank had changed between 2 individuals in this unit. Overall, these preliminary findings suggest that some begging behaviours in captive golden snub-nosed monkeys were not driven by nutritional gain only; instead, we propose that these begging behaviours could be interpreted as attempts at deriving social benefits.     

Fission–Fusion Behavior in Yunnan Snub-Nosed Monkeys (Rhinopithecus bieti) in Yunnan, China

Several species of mammals live in relatively large social groups that temporarily fission or subgroup in response to changes in food availability, predation risk, foraging strategies, and mating competition. Although the dynamics of subgrouping are not well understood, evidence of facultative fission–fusion behavior in species that generally exhibit a highly cohesive group structure may help to clarify the set of ecological and social factors that constrain or affect group size in primates. We here examined patterns of subgrouping in Yunnan snub-nosed monkeys (Rhinopithecus bieti) inhabiting the Baimaxueshan National Nature Reserve in Yunnan, China. Rhinopithecus bieti lives in a large multilevel society consisting of 6–41 one-male, multifemale units (OMUs) and one all-male unit (AMU). Over a 5-yr period from 2003 through 2008, we tracked a group of >450 Rhinopithecus bieti. We recorded the location in the group’s home range where fission and fusion events occurred, the size and number of subgroups, days spent in subgroups, and food availability, and monitored predator sightings. The results indicate that the focal group underwent12 group fission events, all of which occurred between mid-June and July, and all in the same area of the group’s range. During these fissioning events, the AMU also showed subgrouping behavior. In all cases, the presence of bamboo shoots, an important seasonal component of the snub-nosed monkey diet, appeared to trigger subgrouping behavior. The subgroups reunited in other parts of their range after a period of 2–11?d. We found no evidence that the presence of predators had a direct affect on subgrouping behavior in Rhinopithecus bieti, as proposed in previous studies.