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

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

Changes in the structure of the baboon hybrid zone in the Awash National Park,Ethiopia

The zone of hybridization between anubis and hamadryas baboons in the Awash National Park, Ethiopia, evidently changed significantly in the early 1970s. When first studied, by Nagel in 1968, the distribution of adult male phenotypes suggested that the hybrid zone was a narrow, static, genetic sink. In contrast, studies during the 1970s found evidence for a broad hybrid zone intergrading with parental populations and probably expanding. A more detailed investigation of data collected in 1973, presented here, shows that between 1968 and 1973 the distribution of phenotypes changed to a more clinal pattern because of the maturation and successful integration of an extensive cohort of hybrid males. We present a provisional model that accounts for the changes in terms of climatic oscillations, with the hybrid zone tending to expand during periods of climatic instability.     

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.”     

Behavioral variation and reproductive success of male baboons (Papio anubis x Papio hamadryas) in a hybrid social group

We take advantage of an array of hybrid baboons (Papio anubis x Papio hamadryas) living in the same social group to explore the causes and consequences of different male mating strategies. Male hamadryas hold one-male units and exhibit a sustained, intense interest in adult females, regardless of the latter's reproductive state. Anubis baboons, by contrast, live in multi-male, multi-female groups where males compete for females only when the latter are estrous. These two taxa interbreed to form a hybrid zone in the Awash National Park, Ethiopia, where previous work has suggested that hybrid males have intermediate and ineffective behavior. Here, we first examine male mating strategies with respect to morphological and genetic measures of ancestry. We found significant relationships between behavioral measures and morphology; males with more hamadryas-like morphology had more hamadryas-like behavior. However, genetic ancestry was not related to behavior, and in both cases intermediates displayed a previously unreported level of behavioral variation. Furthermore, male behavior was unrelated to natal group. Second, we evaluated reproductive success by microsatellite-based paternity testing. The highest reproductive success was found for individuals exhibiting intermediate behaviors. Moreover, over nine years, some genetically and morphologically intermediate males had high reproductive success. We conclude that the behavior of hybrid males is therefore unlikely to be an absolute barrier to admixture in the region.     

Hepatocystis in populations of baboons (Papio hamadryas s.l.) of Tanzania and Ethiopia

Bloodsmears from 119 yellow baboons (Papio hamadryas cynocephalus) in six groups in Mikumi National Park, Tanzania, and from 189 olive (P.h. anubis) hamadryas (P.h. hamadryas) and hybrid baboons in three groups in Awash National park, Ethiopia showed differing levels of infection with Hepatocystis simiae. 0% to 42% in the Tanzanian groups were carriers of the parasite but none of the Ethiopian baboons was positive. The remarkable absence of H. simiae in the Ethiopian baboons is believed to be related to environmental factors that exclude transmission in the absence of the Culicoides vector.     

Sociological study of a wild group of hybrid baboons betweenPapio anubis andP. hamadryas in the Awash Valley,Ethiopia

A group of hybrid baboons between anubis and hamadryas named the Gorge group was studied for five months in the Awash Valley, Ethiopia. Both morphologically and genetically, anubis features were prevalent in the Gorge group. Three types of subgroups within the group were distinguished: one-male groups, pair groups, and multi-male groups. The joining and parting of subgroups is examined by cluster-analysis. The Gorge group is concluded to be a single social unit, though it was composed of two main clusters. Grooming relations, spacing mechanisms, and sexual relations among its members were analyzed in detail. The dominance relationships among males are clarified in order to be related with their social interactions. Various aspects of the social organization are compared with those of anubis or hamadryas. It is demonstrated that the social structure of the Gorge group showed an intricate mixture of anubis and hamadryas characteristics. It is discussed how such a structure had been formed through hybridization, and what were the factors causing the differences among three types of subgroups.     

Ethological study of the social behavior of hybrid baboons betweenPapio anubis andP. hamadryas in free-ranging groups

The male-female and male-male interactions of hybrid baboons betweenPapio anubis andP. hamadryas were analyzed quantitatively in two free-ranging groups in the Awash Valley, Ethiopia. Morphologically, one group (the Kerrayu group) was closer to hamadryas, while the other (the Gorge group) was closer to anubis. The adult males were classified into four categories; i.e., leaders of one-male units, males in pair units (both in the Kerrayu group), males with a closer appearance to hamadryas, and males with an anubis-like appearance (both in the Gorge group). These categories coincided with the morphological gradient from hamadryas to anubis. Social behavior was described in terms of 53 kinds of behavioral elements identified. In both groups, the closer a male was to being hamadryas in morphology, the more frequent was the aggressive behavior it tended to address toward partner females. The patterns of male-female interactions were compared between one-male units and pair units in the Kerrayu group. In one-male units, females responded immediately with obedient behavior to the males' behavior of directing visual attention toward them. In pair units, females responded with affinitive or avoiding behavior to physical contact by males. The flow of male social behavior was resolved into transitions from one behavioral element to another, and the succession rates for all the observed transitions were independently computed within each male category. By comparing the principal pathways of the behavioral sequences between male categories, 31 “basic pathways” were identified, which were presumed to be common to bothP. anubis andP. hamadryas. The basic pathways were composed of four main behavioral categories, i.e.,Contact, Visual-spacing, Aggressive behavior toward females, andAppeasing behavior toward males. In one-male units, transitions fromVisual-spacing toAggressive behavior were clearly recognized, whereas the principal pathways in pair units lacked such transitions. The frequency distributions of behavioral elements among the above behavioral categories were compared among the four male categories. The more prevalent anubis characters were in morphology, the larger was the proportion thatContact behavior occupied in the total amount of social behavior. The more prevalent hamadryas characters were, the larger was the proportion thatVisual-spacing behavior occupied. The leaders of one-male units showed a higher percentage ofAggressive behavior than did males of the other three categories. A conspicuous difference was observed in the percentage ofAppeasing behavior between the Gorge and Kerrayu groups. It appeared that the high frequency ofAppeasing behavior among males in the Kerrayu group contributed to the spatial cohesion of this group. The similarities of morphology, principal pathways, and frequency distribution of behavior were calculated for every combination of the four male categories. The morphological similarities correlated best with the similarities of principal pathways. It is concluded that the sequential structure of the male social behavior was strongly correlated with the genetic background, while the frequency of social behavior itself was subject to factors other than innate behavioral tendencies, such as the characteristics of the social environment and social context.     

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.     

Sexual dimorphism in two subspecies of Ethiopian baboons (Papio hamadryas) and their hybrids

Sexual dimorphism in mammals has been related to such variables as absolute body size, ecology, and various aspects of social behaviour. Attempts to relate dimorphism to any of these variables have necessarily used small heterogeneous samples to represent the relevant species. We are concerned by the inevitable exclusion of any measure of variability in dimorphism and the consequent impossiblity of assessing the significance of observed interspecific differences. In this paper we describe aspects of sexual dimorphism in anubis,hamadryas, and hybrid baboons from Ethiopia. Samples are large enough to permit a measure of intrapopulation variability. Hamadryas baboons are more dimorphic than anubis in epigamic features, but not in postcanine dentition, nor, contrary to previous reports, in body weight or canine tooth size. Hybrid males are more hamadryas-like and hybrid females more anubis-like, as would be predicted by the proposed mechanism for the establishment of the hybrid zone, namely the capture of anubis females by hamadryas males.     

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     

Early sexual maturity in male hamadryas baboons (Papio hamadryas hamadryas) and its reproductive implications

We present data on sexual maturity in young hamadryas baboon males (Papio hamadryas hamadryas) and its reproductive consequences in a large captive baboon colony. Hamadryas baboons live in a multilevel social system, with one-male units (OMUs) as the smallest social entity. Male leaders of OMUs are believed to monopolize matings within their OMUs; hence mating is believed to be polygynous and monandrous. In a captive colony of hamadryas baboons, we found evidence that young males less than 4 years old fathered at least 2.5% of 121 offspring born subsequent to vasectomy of all adult males, and males aged 4-5 years fathered at least 16.5% of the offspring. Additional evidence that these young males are able to sire offspring came from a morphological comparison of sperm from hamadryas males of different ages. The sperm of a 48-month-old hamadryas baboon were morphologically indistinguishable from viable sperm from adult males, whereas sperm from a 45-month-old male showed some aberrations. If successful copulations by adolescent males constitute a regular pattern even in free-ranging hamadryas baboons, a hamadryas male's chances to reproduce would not be limited to his role as an OMU leader as previously assumed, and a male's reproductive career would consist of two phases: the adolescent phase, and the OMU leader male phase.     

Characteristics of hamadryas-like male baboons living in anubis baboon troops in the Awash hybrid zone, Ethiopia.

In the twenty-two years since the Awash baboon hybrid zone was first described, about 25-30 hamadryas or hamadryas-like hybrid males have taken up residence in anubis baboon groups. Most enter as mature adults, though some may immigrate as juvenile followers. Long-term tracking of known immigrants indicates that they may reside for four years or more in their adopted troop, during which time they establish a series of comparatively short-term harems, and probably sire hybrid offspring. "Abductions" of anubis females to hamadryas troops, as postulated by early observers, were not seen, though their occurrence cannot be ruled out. Younger, more recent immigrants tend to be "purer" hamadryas in phenotype, perhaps reflecting a more distant origin, or a change in the composition of neighboring hamadryas populations. Coexisting hamadryas and anubis show no signs of reproductive isolation by behavioral barriers, and evidently belong to a single "recognition species."     

Monoamine Neurotransmitter Metabolites in the Cerebrospinal Fluid of a Group of Hybrid Baboons (Papio hamadryas × P. anubis)

Comparatively little is known about the pathways of proximate causation that link divergent genotypes, via neurophysiological differences, to distinct, species-specific social behaviors and systems. One approach to the problem compares gross activity levels of monoamine neurotransmitters (norepinephrine, dopamine, and serotonin), evidenced by their metabolites —3-methoxy-4-hydroxyphenylglycol (MHPG), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA), respectively— in cerebrospinal fluid (CSF). We have applied this method to Papio hamadryas and P. anubis, closely related baboon species with divergent social behavior, living in the Awash National Park (ANP), Ethiopia. We had previously shown that adult males of the two species differ in the ratio of HVA to 5-HIAA, and in concentrations of MHPG and HVA, but not 5-HIAA. Here, we compare monoamine metabolite levels of the parental species with those of 49 members of a naturally formed, multigenerational hamadryas × anubis hybrid group. We cage-trapped the baboons in July 1998, sampled their CSF by cisternal puncture, and assayed monoamine metabolites by high-performance liquid chromatography. Previous findings suggested, anomalously, that hybrid males showed the high 5-HIAA levels predicted by the low-serotonin–early-dispersal hypothesis (originally based on observation of rhesus macaques, Macaca mulatta), while hamadryas did not. The present study failed to find higher 5-HIAA levels in hybrids, resolving the anomaly, but leaving the previous result unexplained. Among adult females (underrepresented in our sample) and juveniles, metabolite levels of the hybrids did not differ significantly from either parental species. Overall, adult male hybrids resembled anubis in HVA and HVA/5-HIAA ratio, but did not show the low MHPG levels characteristic of that species. Consistent with a significant genetic influence on species differences in these metabolites, the adult hybrids showed intermediate means and greater intra-population diversity than the parental species for most variables, but showed no indication of hybrid dysgenesis in the form of low intermetabolite correlation. To the contrary, an enhanced HVA–MHPG correlation in the hybrids suggested a species-associated factor (not necessarily genetic) influencing both of these monoamine neurotransmitter systems.     

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

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

Humans as primates: The social relationships of Efe pygmy men in comparative perspective

The Efe are short-statured specialized hunger-gatherers living in the moist tropical forest in northeast Zaire. They live in small mobile groups averaging 18 individuals and practice viripatrilocal residence — what primatologists refer to as male philopatry and female dispersal. This study uses methods commonly employed by primatologists to study the social relationships of Efe men. It compares their association and affiliation patterns with those of two nonhuman primate species that show male philopatry and female transfer. The analyses of 376 hr of focal behavior observations on 16 Efe men reveal that the majority of their associations were with other adult men. Men associated preferentially with kin over non-kin, and with close kin more than with distant kin. Men's close relationships, or companionships,sensu Smuts' (1985) friendships among anubis baboons, were predominantly with other adult men; however, each man who cohabited with a woman had his strongestcompanionship by far with that woman. These quantitative measures of affinity are consistent with the Efe's pattern of viripatrilocal residence, where-by males remain in their natal group with their close male kin and females join or are recruited from other patriclans. The social relationships of Efe men are similar in some respects to those of hamadryas and chimpanzees; however, Efe men's social networks are larger and more fluid. We speculate that the explanation proposed for male philopatry and female dispersal among nonhuman primates also applies to the Efe.     

Hematocrits of free-ranging baboons: variation within and among populations

Hematocrits among free-ranging baboons (Papio hamadryas subsp.), from Awash in Ethiopia and Mikumi in Tanzania, varied by region, sex, age, and season of collection. Tanzanian animals had higher mean values than Ethiopian, and hematocrits were higher in the dry season. We discuss the comparability of field and laboratory data and possible reasons for the observed variation.     

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.     

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.     

One-male groups and intergroup interactions of mountain baboons

The behavioral ecology of mountain baboons, Papio ursinus,cuts across the traditional dichotomy between savannah and desert baboons, providing fresh opportunities to examine socioecological relationships. Mountain baboons were studied at a site where covariation in altitude and group size helps to clarify the influence of ecology on social behavior. One-male groups and lone males were regularly found in the highest-altitude zones. In encounters with multimale groups, a one-male group retreated; the group’s single male attacked his females, herding them far away from the multimale group. The male himself then approached and watched (and often loud-called at) this group. In a two-male group, the younger male herded the females, while the older sometimes defended the group. One-male groups did not show regular, stable aggregations, but two such groups seasonally coordinated their ranging “in tandem.” Ecological explanations for these behaviors and their relationship to the behavior of hamadryas baboons are evaluated, and a new theory of the origin of one-male groups in baboons is developed.     

Baboons, Water, and the Ecology of Oxygen Stable Isotopes in an Arid Hybrid Zone

Abstract Baboons regularly drink surface waters derived from atmospheric precipitation, or meteoric water. As a result, the oxygen isotope (δ(18)O) composition of their tissues is expected to reflect that of local meteoric waters. Animal proxies of the oxygen isotope composition of meteoric water have practical applications as paleoenvironmental recorders because they can be used to infer aridity and temperature in historic and fossil systems. To explore this premise, we measured the δ(18)O values of hair from two baboon species, Papio anubis and Papio hamadryas, inhabiting Awash National Park, Ethiopia. The hybridizing taxa differ in their ranging behavior and physiological response to heat. Papio hamadryas ranges more widely in the arid thornbush and is inferred to ingest a greater proportion of leaf water that is enriched in (18)O as a result of evaporative fractionation. It is also better able to conserve body water, which reduces its dependence on meteoric waters depleted in (18)O. Taken together, these factors would predict relatively higher δ(18)O values in the hair (δ(18)O(hair)) of P. hamadryas. We found that the δ(18)O(hair) values of P. hamadryas were higher than those of P. anubis, yet the magnitude of the difference was marginal. We attribute this result to a common source of drinking water, the Awash River, and the longer drinking bouts of P. hamadryas. Our findings suggest that differences in δ(18)O values among populations of Papio (modern or ancient) reflect different sources of drinking water (which might have ecological significance) and, further, that Papio has practical value as a paleoenvironmental recorder.