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.”     

Alternative routes to the leader male role in a multi-level society: follower vs. solitary male strategies and outcomes in hamadryas baboons

The nested one-male units (OMUs) of the hamadryas baboon are part of a complex social system in which "leader" males achieve near exclusive mating access by forcibly herding females into permanent consortships. Within this multi-level social system (troops, bands, clans and OMUs) are two types of prereproductive males--the follower and solitary male--whose different trajectories converge on the leader role. Here we compare OMU formation strategies of followers, who associate with a particular OMU and may have social access to females, with those of solitary males, who move freely within the band and do not associate regularly with OMUs. Data were derived from 42 OMU formations (16 by followers and 26 by solitary males) occurring over 8 years in a hamadryas baboon band at the Filoha site in Ethiopia. "Initial units" (IUs) with sexually immature females (IU strategy) were formed by 44% of followers and 46% of solitary males. The remaining followers took over mature females when their leader was deposed (challenge strategy) or disappeared (opportunistic strategy), or via a seemingly peaceful transfer (inheritance strategy). Solitary males took over mature females from other clans and bands, but mainly from old, injured or vanished leaders within their clan (via both the challenge and opportunistic strategies). Former followers of an OMU were more successful at taking over females from those OMUs than any other category of male. Despite this advantage enjoyed by ex-follower leaders, ex-solitary leaders were equally capable of increasing their OMU size at a comparable rate in their first 2 years as a leader. These results demonstrate the potential for males to employ both multiple roles (follower vs. solitary male) and multiple routes (IU, inheritance, challenge, opportunistic) to acquire females and become a leader male in a mating system characterized by female defense polygyny in a competitive arena.     

One-male units and clans in a colony of hamadryas baboons (Papio hamadryas hamadryas): effect of male number and clan cohesion on feeding success

In the multilevel societies of hamadryas baboons, adult males can be attached to single one-male units (OMUs) or to clans containing several such OMUs. This paper examines the effect of male number and rivalry between males within a clan on their ability to compete for access to a clumped food resource. The data come from a study of a multilevel colony of hamadryas baboons (Papio hamadryas hamadryas) housed at the Madrid Zoo. The colony consisted of 12 harem-holding males and 40 sexually mature females, and was organized into five single OMUs and two clans (containing three and four OMUs, respectively). The top-ranking male of one of the clans was removed and later reintroduced, so the study involved an analysis of the composition of clans and OMUs and of the males' use of the feeding area across three study periods: preseparation, separation, and reintroduction. The findings reported indicate that both males and females derived clear advantages in the context of contest competition for access to clumped food if they were members of clans, because the males and females from large clans had a feeding advantage over those from smaller clans and single OMUs. Furthermore, rivalry among males within the clan reduced their ability to compete for food against males outside their clan. This paper provides empirical evidence for one of the potential advantages that hamadryas males may enjoy if they are attached to clans, and also provides empirical support for the general hypothesis that a large number of males in a group may provide fitness-related benefits to the group members, provided they are able to cooperate with each other.     

Copulation patterns in captive hamadryas baboons: a quantitative analysis

For primates, as for many other vertebrates, copulation which results in ejaculation is a prerequisite for reproduction. The probability of ejaculation is affected by various physiological and social factors, for example reproductive state of male and female and operational sex-ratio. In this paper, we present quantitative and qualitative data on patterns of sexual behaviour in a captive group of hamadryas baboons (Papio hamadryas), a species with a polygynous–monandric mating system. We observed more than 700 copulations and analysed factors that can affect the probability of ejaculation. Multilevel logistic regression analysis and Akaike’s information criterion (AIC) model selection procedures revealed that the probability of successful copulation increased as the size of female sexual swellings increased, indicating increased probability of ovulation, and as the number of females per one-male unit (OMU) decreased. In contrast, occurrence of female copulation calls, sex of the copulation initiator, and previous male aggression toward females did not affect the probability of ejaculation. Synchrony of oestrus cycles also had no effect (most likely because the sample size was too small). We also observed 29 extra-group copulations by two non-adult males. Our results indicate that male hamadryas baboons copulated more successfully around the time of ovulation and that males in large OMUs with many females may be confronted by time or energy-allocation problems.     

Female "dispersal" in hamadryas baboons: transfer among social units in a multilevel society

Unlike most cercopithecines, hamadryas baboons (Papio hamadryas hamadryas) are characterized by female-biased dispersal. To clarify this pattern within the context of their hierarchical social system (comprising one-male units, clans, bands, and troops), we report here 7 years of data on female transfers among social units in wild hamadryas baboons in Ethiopia. Female tenure in one-male units (OMUs) ranged from 1 to 2,556 days (N = 208) and survival analysis revealed a median tenure length of 1,217 days (40 months). Changes in OMU membership consisted almost exclusively of takeovers by males, not voluntary transfer. Of 130 takeovers, 67% occurred within the band and 33% across bands, and, of the 22 takeovers for which we have clan membership data, 77% occurred within, not between, clans. These results reinforce the notion that hamadryas female dispersal is not analogous to sex-biased dispersal in other taxa, because (1) at least in Ethiopian populations, females do not disperse voluntarily but are transferred, often forcibly, by males; (2) only dispersal between bands will promote gene flow, whereas females are most often rearranged within bands; (3) hamadryas females undergo social dispersal but not usually locational dispersal; and (4) while male hamadryas are far more philopatric than females, they have been observed to disperse. It thus appears that the ancestral baboon pattern of female philopatry and male dispersal has evolved into a system in which neither sex is motivated to disperse, but females are forcibly transferred by males, leading to female-mediated gene flow, and males more rarely disperse to find females.     

Dominance relationships among male hamadryas baboons (Papio hamadryas)

The concept of dominance has been shown to be useful in describing and predicting social interactions in group-living animals. However, the dominance relationships among adult hamadryas males (Papio hamadryas) are poorly understood, and systematic data are missing from the literature. This study investigated dominance relationships among male hamadryas baboons by applying novel statistical techniques to systematic detailed data on agonistic interactions. We also analyzed the dominance relationship with male age and evaluated the association between dominance and access to mating partners (i.e. the number of adult females per one-male unit (OMU)), food resources (i.e. monopolization of feeding areas), and greeting interactions. The derived dominance indexes showed that, in general, leader males were dominant over followers, and that dominance ability did not correlate with male age. Individual dominance values were very close to each other, suggesting that dominance relationships among hamadryas males were not very rigid. In addition, dominance values were positively correlated with number of adult females per OMU but not with feeding priority. Finally, greeting interactions occurred more frequently between individuals with similar dominance values and with low levels of dominance decidedness. We suggest the need of further studies, especially in wild populations, to confirm our findings.     

The Socioecology of Network Scaling Ratios in the Multilevel Society of Hamadryas Baboons (Papio hamadryas hamadryas)

Multilevel or modular societies characterize a range of mammalian taxa, allowing social groups to fission and fuse in response to ecological factors. The modular society of hamadryas baboons has previously been shown to consist of 4 levels: troop, band, clan, and one-male unit (OMU). A recent study by Hill et al. (Biology Letters 4:748–751, 2008) revealed a mean scaling ratio across successive levels of multilevel societies of ca. 3; this was consistent across elephants, orca, geladas, and hamadryas baboons. Here we reanalyze the scaling ratio for hamadryas baboons with previously unavailable data from Filoha. Our analysis revealed a mean scaling ratio for hamadryas of 3.28 without data on the hamadryas clan layer of organization at Filoha, but a ratio of 6.17 with these data included. This discrepancy is due to the large clan and band sizes at Filoha yielding a larger than average gap between the OMU and the clan. Further analysis revealed subsets of OMUs within clans, suggesting a 5th level of society in this population. When this 5th layer of social structure is included in the analysis, the scaling ratio at Filoha is consistent with that of other hamadryas populations and other taxa. These results suggest that a consistent mammalian scaling ratio can be used to detect previously hidden levels of organization within societies and to predict their sizes in taxa for which detailed behavioral data are not available.     

Human–hamadryas baboon (Papio hamadryas) conflict in the Wonchit Valley,South Wollo,Ethiopia

Understanding the extent of human–primate conflict is crucial to the development of conservation and management strategies. We carried out this study in an unprotected area of central Ethiopia to examine the magnitude of human–hamadryas baboon (Papio hamadryas) conflict and to assess the attitude of local farmers towards baboons in Wonchit Valley. In 2014, we interviewed 119 adult respondents using a structured questionnaire. Local farmers considered hamadryas baboons to be the major pest in the area. All respondents reported that hamadryas baboons caused crop raiding and small livestock predation in the region. Respondents reported that a shortage of fruit producing wild trees and ready availability of crops were the main causes of conflict between farmers and hamadryas baboons. We found that hamadryas baboons damaged cereal crops at dusk and dawn during full moonlight, and most (89.9%) respondents claimed that they were not interested in hamadryas baboon conservation. Our results indicate that human–hamadryas baboon conflict has a strongly negative impact on both baboon conservation and local farmers. We suggest that to mitigate the human–hamadryas baboon conflict, job opportunities such as beekeeping should be introduced in the region.     

The fourth level of social structure in a multi‐level society: ecological and social functions of clans in hamadryas baboons

Hamadryas baboons are known for their complex, multi‐level social structure consisting of troops, bands, and one‐male units (OMUs) [Kummer, 1968. Social organization of hamadryas baboons. Chicago: The University of Chicago Press. 189p]. Abegglen [1984. On socialization in hamadryas baboons: a field study. Lewisburg, PA: Bucknell University Press. 207p.] observed a fourth level of social structure comprising several OMUs that rested near one another on sleeping cliffs, traveled most closely together during daily foraging, and sometimes traveled as subgroups independently from the rest of the band. Abegglen called these associations “clans” and suggested that they consisted of related males. Here we confirm the existence of clans in a second wild hamadryas population, a band of about 200 baboons at the Filoha site in lowland Ethiopia. During all‐day follows from December 1997 through September 1998 and March 2005 through February 2006, data were collected on activity patterns, social interactions, nearest neighbors, band fissions, and takeovers. Association indices were computed for each dyad of leader males, and results of cluster analyses indicated that in each of the two observation periods this band comprised two large clans ranging in size from 7 to 13 OMUs. All band fissions occurred along clan lines, and most takeovers involved the transfer of females within the same clan. Our results support the notion that clans provide an additional level of flexibility to deal with the sparse distribution of resources in hamadryas habitats. The large clan sizes at Filoha may simply be the largest size that the band can split into and still obtain enough food during periods of food scarcity. Our results also suggest that both male and female relationships play a role in the social cohesion of clans and that males exchange females within clans but not between them. Am. J. Primatol. 71:948–955, 2009. © 2009 Wiley‐Liss, Inc.     

DNA fingerprinting and the problems of paternity determination in an inbred captive population of guinea baboons (Papio hamadryas papio)

Multilocus DNA fingerprinting was carried out on 65 individuals from a captive colony of guinea baboons (Papio hamadryas papio) at Brookfield Zoo, in order to determine the allocation of reproductive success among 7 active males. DNA fingerprinting was found to reveal very low levels of genetic variability in the study population, rendering discrimination of different levels of relatedness, and hence paternity, impossible. A method was therefore developed for emphasizing the region of the fingerprint pattern which revealed the greatest level of band variability, and the effect of this experimental modification on band sharing statistics was tested. Band sharing coefficients among unrelated individuals were significantly lower using the modified system, which was then applied to paternity testing in the whole population. However even when using the modified system, of the 33 offspring analyzed only 4 could be assigned solely to 1 male, 14 offspring were assigned to 1 of 2 males, 7 offspring had 3 potential fathers, and the remainder had 4 or more possible fathers. The implications of the limitations of these data for behavioural studies and genetic management of captive populations are discussed.     

Origin and fate of a one-male savanna babbon group formed by fissioning

An adult male chacma baboon,Papio hamadryas ursinus, emigrated from his habituated natal group at age 100 months and joined a neighboring multimale-multifemale group. Subsequently this male, together with eight adult females, all with infants <1 year old, formed a one-male group (OMU). The male was the only adult male in this group for over 200 days. Circumstantial evidence shows that shared parentage of the infants with this male determined which females joined the new group. In addition, 10 juveniles younger than 4.5 years joined the new group. Based upon persistent close physical association, especially at sleeping sites, these juveniles were presumed to be the older independent progeny of the eight adult females. Thus, the founding elements of the new group were the adult male and partial matrilines—mothers, their infants, and their independent juvenile offspring. The OMU status of the group ended with the sequential intrusion of three males known to be low ranking in other groups. The first of these intruders was successful in joining the OMU in spite of the OMU male's earlier successes in rebuffing this and other potentially high-ranking males. Six additional males later entered the fission group during a 6-month interval. Two of them outranked the original male. All additional males present in the last 100 days of observations came from the same group, which was not the group of origin of the females.     

Tool use in captive hamadryas baboons

A subadult male of a captive harem of hamadryas baboons learned, by instrumental trial-and-error learning, to use a tool to supply food for the harem. The behavior did not spread through the harem by imitation. The subadult male's rank in the harem's dominance hierarchy did not change as a result of his tool use.     

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.     

Male dispersal in a provisioned multilevel group of Rhinopithecus roxellana in Shennongjia Nature Reserve, China

Most Old World monkeys show male-biased dispersal. We present the first systematic data on male dispersal in a provisioned multilevel group of Rhinopithecus roxellana, based on 4.5 years of field observations in Shennongjia National Nature Reserve, China. We evaluated both ultimate (inbreeding avoidance and male mating competition) and proximate (food availability and predation risk) factors influencing male dispersal. The focal group contained 34-53 individuals, in 3-4 one-male units (OMUs) and 1 all-male unit (AMU). We observed 37 dispersal events involving 10 of 11 adults, 7 of 8 subadults, and 7 of 15 juveniles. Most interunit transfers within the focal group occurred around the months of mating season. Adult males competed for the leader positions of OMUs mainly through aggressive takeovers, and young males transferred from the OMUs to the AMU at the median age of 41 months, forced out by leader males. No young males older than 4 years remained in natal or non-natal OMUs. The male mating competition hypothesis was supported. The young males emigrated voluntarily from the focal group at the average age of 58.6 months, and no young emigrating male was observed to return, suggesting inbreeding avoidance also played a role in the dispersal of young males. Most emigration/immigration events were parallel dispersal and occurred during intergroup encounters, suggesting increased predation risk during the dispersal period. Males were more likely to emigrate/immigrate during the months when preferred foods were most available. We compared the dispersal patterns in R. roxellana with those in gelada baboons and hamadryas baboons, both living in multilevel societies. Similar to R. roxellana, young male geladas disperse at puberty, but they may return and breed in their natal groups. Males in hamadryas also disperse, but much less commonly than in R. roxellana. Provisioning may have influenced results, and confirming studies on unprovisioned groups would be valuable.     

Affiliation Among Females in Wild Hamadryas Baboons (Papio hamadryas hamadryas)

Previous researchers of hamadryas baboons have described a star-shaped sociogram, whereby the strongest social bonds within hamadryas one-male units are between a leader male and his females and bonds among females are weak by comparison. This type of social organization is also known as cross-bonding to distinguish it from the female-bonding found in most papionin monkeys. Models of female primate socioecology suggest that hamadryas baboons lack female bonding due to their reliance on scarce, widely-dispersed food resources. Here, I report observational data from a wild population of hamadryas baboons in Ethiopia indicating that, while females varied widely in their frequency of social interaction with other females, most females spent about as much social time with other females as they did with the leader male and some females even crossed unit boundaries to interact with one another. The size of a unit was positively correlated with the tendency of its females to interact with other females and was negatively correlated with the tendency of its females to interact with the leader male. Females were equally likely to spend social time with other females whether or not the leader male was available for social interaction at the time. Overall, this study suggests that a star-shaped sociogram does not characterize all hamadryas baboons and that female hamadryas may be, to some extent, female-bonded as well as cross-bonded. The lack of more pronounced female bonding in hamadryas is probably due to the behavior of males rather than to ecological factors.     

Crossing the Red Sea: phylogeography of the hamadryas baboon, Papio hamadryas hamadryas

The hamadryas baboon (Papio hamadryas hamadryas) is found both in East Africa and western Arabia and is the only free-ranging nonhuman primate in Arabia. It has been hypothesized that hamadryas baboons colonized Arabia in the recent past and were possibly even transported there by humans. We investigated the phylogeography of hamadryas baboons by sequencing a portion of the control region of mtDNA in 107 baboons from four Saudi Arabian populations and combing these data with published data from Eritrean (African) P. h. hamadryas. Analysis grouped sequences into three distinct clades, with clade 1 found only in Arabia, clade 3 found only in Africa, but clade 2 found in both Arabian and African P. h. hamadryas and also in the olive baboon, P. h. anubis. Patterns of variation within Arabia are neither compatible with the recent colonization of Arabia, implying that baboons were not transported there by humans, nor with a northerly route of colonization of Arabia. We propose that hamadryas baboons reached Arabia via land bridges that have formed periodically during glacial maxima at the straits of Bab el Mandab in the southern Red Sea. We suggest that the genetic differentiation of Arabian from African populations suggests that Arabian populations have a higher conservation status than recognized previously.     

Cerebrospinal Fluid Monoaminergic Metabolites in Wild Papio anubis and P. hamadryas are Concordant with Taxon-specific Behavioral Ontogeny

We used a cross-sectional sample to compare ontogenetic trajectories in the concentrations of monoamine neurotransmitter metabolites in cerebrospinal fluid of wild anubis (Papio anubis, n = 49) and hamadryas (P. hamadryas, n = 54) baboons to test the prediction that they would differ, especially in males, in association with their distinct behavioral ontogenies. Values of all 3 metabolites [3-methoxy-4-hydroxyphenylglycol (MHPG), the norepinephrine metabolite; 5-hydroxyindoleacetic acid (5-HIAA), the serotonin metabolite; and homovanillic acid (HVA), the dopamine metabolite] declined consistently with dentally-calibrated maturation, and few taxon-related differences were apparent among juveniles. Adult females were too few for adequate comparison, but a discriminant function suggested that they might differ by taxon. Adult males of the 2 species differed strikingly from juveniles and from each other. Contrary to our initial hypothesis, adult male anubis had significantly lower HVA and MHPG, and higher 5-HIAA levels, than predicted from the overall, age-related trend, and MHPG continued to decline with age among adults. As young adults, male hamadryas had low 5-HIAA and a high HVA/5-HIAA ratio, while older males [normatively one-male unit (OMU) leaders] showed a reversal in the trend, with 5-HIAA rising and the HVA/5-HIAA ratio tending to fall. We speculate that the results are related to the dispersing and philopatric ontogenies of anubis and hamadryas males, respectively. Adult male anubis, whose fitness depends on building social networks with nonkin, have high relative serotonin activity, commonly associated with greater social circumspection and skill. Young adult male hamadryas, living among agnatic kin and mating opportunistically, exhibit low 5-HIAA levels, generally associated with impulsivity and social irresponsibility. This reverses as a male approaches the age at which he is normatively the leader of a one-male unit (OMU), and his fitness depends on his maintaining stable relationships with other leaders and with females. An erratum to this article can be found at     

Function of Notification in Papio hamadryas

Notification is a form of ritualized greeting behavior performed by adult male hamadryas baboons (Papio hamadryas). Originally observed in the wild when harem leaders signaled the direction of travel to their followers on daily foraging marches, its true function is unknown. Notification involves the approach of an adult male baboon to another male, the presentation of his hindquarters, then retreat. Researchers have previously linked notification to aggression avoidance, appeasement, and the dominance-subordination relationship between males. We observed instances of notification over 6 mo among 8 adult males in a troop of 61 captive-bred hamadryas baboons at Paignton Zoo Environmental Park, Devon, UK. We compared observation sessions in which notification occurred with matched control periods. We classified different forms of notification according to the recipient’s response: presenting, mounting, touching of the buttocks or genitals, or ignoring. Results suggest that different forms of notification may have different functions, including submission, alliance, and peacekeeping but not general greeting, recruitment, or appeasement.     

Dental eruption schedules of wild and captive baboons

Dental eruption schedules previously used to age wild baboons have in the past derived from studies of captive animals housed under standard conditions and fed standard laboratory diets. This paper reports for the first time eruption schedules derived from wild baboons, the yellow baboons (Papio hamadryas cynocephalus) of Mikumi National Park, Tanzania, and compares these schedules with those of other baboon subspecies inhabiting both similar and dissimilar environments. Eighteen males and twelve females from the Viramba groups, ranging in age from 21 to 103 months, were trapped, and dental impressions and notes were made of the state of eruption of each tooth. Eruption of all teeth were delayed at Mikumi relative to the baboon standards derived from the captive animals at the Southwest Foundation for Biomedical Research, San Antonio, Texas. Teeth of the canine-premolar 3 complex and third molars were most delayed, erupting up to a year and a half later than their counterparts from captive animals. Comparison with data on hamadryas baboons from Erer-Gota in Ethiopia revealed that both the hamadryas and yellow subspecies of baboons, with different genetic backgrounds and living under markedly different environmental conditions, followed the same schedule. This constancy of developmental schedules suggests that these Mikumi data may reasonably be used as standards for other wild baboon populations and that acceleration of dental maturation, as well us maturation of other somatic systems in captivity, is another manifestation of the short-term adaptive plasticity of the baboon species as a whole.