Verreaux's eagles (Aquila verreauxi) as potential predators of hamadryas baboons (Papio hamadryas hamadryas) in Eritrea

In this paper we describe for the first time encounters of Verreaux's eagle (Aquila verreauxi) with hamadryas baboons (Papio hamadryas hamadryas) in the central highlands of Eritrea (15° 22′ N, 38° 58′ E, 2300 m). During 12 h of observation on 4 days, we observed four encounters of Verreaux's eagles with baboons, of which three can be classified as possible attacks. The baboons always responded with alarm calls. In three cases some immatures rushed to adult group members and clung to them, particularly to the adult male. Adult males threatened the eagle, and the whole group did not flee. The response of baboons towards smaller raptors like tawny eagles (Aquila rapax) and black kites (Milvus migrans) was very different. The adult baboons gave no alarm barks but scanned the raptors. The permanent presence of a pair of Verreaux's eagles in the home range of the baboons may represent a considerable predation pressure, at least for immature baboons. Am. J. Primatol. 47:61–66, 1999. © 1999 Wiley‐Liss, Inc.     

Influence of rainfall on sleeping site choice by a group of anubis baboons (Papio anubis)

For diurnal nonhuman primates, shifting among different sleeping sites may provide multiple benefits such as better protection from predators, reduced risk of parasitic infection, and closer proximity to spatially and temporally heterogeneous food and water. This last benefit may be particularly important in sleeping site selection by primates living in savanna‐woodlands where rainfall is more limited and more seasonally pronounced than in rainforests. Here, we examined the influence of rainfall, a factor that affects food and water availability, on the use of sleeping sites by anubis baboons (Papio anubis) over two 13‐month study periods that differed in rainfall patterns. We predicted that during wet periods, when food and water availability should be higher, the study group would limit the number of sleeping sites and would stay at each one for more consecutive nights than during dry periods. Conversely, we predicted that during dry periods the group would increase the number of sleeping sites and stay at each one for fewer consecutive nights as they searched more widely for food and water. We also predicted that the group would more often choose sleeping sites closer to the center of the area used during daytime (between 07:00 and 19:00) during wet months than during dry months. Using Global Positioning System data from collared individuals, we found that our first prediction was not supported on either monthly or yearly timescales, although past monthly rainfall predicted the use of the main sleeping site in the second study period. Our second prediction was supported only on a yearly timescale. This study suggests that baboons’ choice of sleeping sites is fluid over time while being sensitive to local environmental conditions, one of which may be rainfall.     

Conflict management by hamadryas baboons (Papio hamadryas hamadryas) during crowding: a tension-reduction strategy

Primates change a variety of behavioral responses during short-term exposure to crowding. Under crowded conditions, rates of aggression, submissive behavior, and affiliative behavior may increase or decrease. Different patterns of change among these three categories of response have been interpreted as various coping "strategies" for managing the increased risk of conflict under crowded conditions. Grooming is of particular interest because this behavior is known to have a calming influence on the recipient and could be used to manage conflict under tense situations. A captive group of nine hamadryas baboons (Papio hamadryas hamadryas) composed of two harems was observed under short-term crowding to determine whether this species adopts conflict-management strategies similar to those described in other primates. The aggression, submission, affiliation, and displacement activities of the six adults in the group (two males and four females) were recorded, and behaviors in their small indoor quarters was compared with baseline behaviors in the outdoor section of their enclosure, which had over 10 times more space. Repeated-measures analysis of variance (ANOVA) was used to compare behavioral rates during crowding with baseline rates recorded immediately after crowding and during matched controls collected at the same time of day as the crowding sessions. Aggression and submission rates did not change significantly across conditions. Huddling together and proximity increased during crowding, and females increased grooming of their harem male during crowding. Displacement activities (e.g., pacing and self-grooming) increased during crowding, but scratching, an indicator of anxiety in primates, did not. The pattern of behavior exhibited by this group conforms to an active "tension-reduction" strategy in which animals successfully reduce the higher risk of aggression during crowding.     

Testing the function of reconciliation and third-party affiliation for aggressors in hamadryas baboons (Papio hamadryas hamadryas)

In social groups, agonistic conflicts can have different negative consequences. Several post-conflict interactions have been suggested as post-conflict management behaviors to mitigate those negative effects. In this study, we investigated the function of two post-conflict behaviors--reconciliation and aggressor-initiated third-party affiliation--on the aggressor's levels of post-conflict anxiety and aggression in a large colony of hamadryas baboons. We also examined variation in the aggressor's levels of post-conflict anxiety as a function of relationship quality between the opponents as predicted by the Integrated Hypothesis. We found that after conflicts hamadryas baboon aggressors showed increased rates of anxiety-related behaviors and that they were also more likely to be involved in renewed aggressive interactions. Although both reconciliation and aggressor-initiated third-party affiliation reduced the probability of receiving post-conflict aggression, only reconciliation reduced the rates of anxiety-related behaviors, suggesting that the aggressors' post-conflict anxiety might be owing mainly to the damage that the conflict causes to their relationship with the victim. Furthermore, aggressor's rates of post-conflict anxiety were higher after conflicts with individuals with whom they had a high-quality relationship, supporting the idea that levels of post-conflict anxiety mediate the occurrence of reconciliation depending on the quality of the relationship with former opponent as predicted by the Integrated Hypothesis.     

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.     

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.     

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.     

Rank and grooming reciprocity among females in a mixed-sex group of captive hamadryas baboons

In a mixed-sex, captive group of hamadryas baboons (Papio hamadryas hamadryas) we investigated whether female grooming relationships are affected by their dominance ranks. Seyfarth's [1977] grooming for support model and Barrett et al.'s [1999] biological market model both predict that in primate groups where competition for monopolizable resources is high, grooming among females is based, at least partly, on the interchange of grooming for rank-related benefits, and that rank thus influences the distribution of grooming in females. Contrary to this prediction, our results show that despite the existence of a linear dominance hierarchy, rather strict dominance relationships, and high food-related aggression rates, grooming among female hamadryas baboons is not affected by rank and is only exchanged for itself. This is understandable since rank differences in our study group only result in differential access to limited, preferred food items that are not actively shared. Although some females are more likely to tolerate one another at the food pile, this tolerance is not determined by their grooming efforts and interchange of grooming for rank-related benefits does not occur. We conclude that female hamadryas baboons groom others in order to be groomed by them, which is supported by our observation that grooming reciprocity within a dyad increases when more grooming occurs in this dyad. Our results indicate that grooming is indeed a valuable commodity in itself, probably because of its stress- and tension-reducing effect. Based on our findings, the existing groom trade model is extended to include circumstances in which monopolizable resources are available but are not traded for grooming.     

Infant mortality after takeovers in wild Ethiopian hamadryas baboons

In this work we report the first observational evidence of infanticide in wild hamadryas baboons. The study group inhabits the lowlands of the northern Rift Valley in Ethiopia and has been under observation for over 1,200 hr, on and off, since October 1996. Here we report observations from August and September 2002 of the consequences of two takeovers of known females with black infants. After the first takeover, the respective infant disappeared and was presumed dead within 11 days of the takeover. After the second takeover, the infant incurred repeated severe aggression from its mother's new leader male and eventually died 4 days after the takeover. We interpret these findings as support for the sexual selection hypothesis regarding male infanticide. We suggest that hamadryas leader males usually protect infants born into their units, but may withhold this protection-or even directly attack and kill infants-after takeovers.     

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.     

Hormonal correlates of ontogeny in baboons (Papio hamadryas anubis) and mangabeys (Cercocebus atys)

This study investigates the relationship between serum hormone levels and morphometrics during ontogeny in olive baboons (Papio hamadryas anubis) and sooty mangabeys (Cercocebus atys), to test hypotheses about the endocrine regulation of species size differences. First, we expect that levels of hormones and binding proteins predict size change during ontogeny in both species. Second, a high level of integration among the hormones and binding proteins analyzed is expected, with the implication that they act in combination to influence the development of body size and shape. Utilizing a mixed longitudinal sample, we compare change in 18 different measurements, which reflect overall size growth as well as growth in length and circumference, with levels of six growth-related hormones and binding proteins. We examine the relationship between hormone and binding protein levels and morphometrics, using multivariate analyses and "arithmetically-estimated" velocity curves of hormones, binding proteins, to characterize how the endocrine factors analyzed relate to growth. Results suggest that levels of these endocrine factors can be used to predict local and overall growth during ontogeny and that integration between multiple hormone axes is indicated. While important for growth in both species, ontogenetic changes in hormone and binding protein levels are more tightly correlated with changes in morphometric measurements in baboons than mangabeys. These results have important implications for understanding why some smaller-bodied species have higher absolute growth-related hormone levels than larger-bodied species.     

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.     

Dental microwear in anubis and hybrid baboons (Papio hamadryas, sensu lato) living in Awash National Park, Ethiopia

We describe dental microwear in baboons (Papio hamadryas sensu lato) from the anubis-hamadryas hybrid zone of Awash National Park, Ethiopia, outline its variation with sex and age, and attempt to relate the observed microwear pattern to environment and diet. Casts of the maxillary second molar of 52 adult and subadult individuals of both sexes were examined with a scanning electron microscope at x 500. Digitized micrographs were taken at a consistent location on facet 9, and microwear was recorded with an image analysis software package. Univariate and multivariate statistics were used to investigate the shape, size, and density of microwear features. The overall pattern of microwear exhibits an unusual combination of high feature density, with numerous small pits and relatively wide striations, and a high correlation between width of pits and striations across individuals. We interpret this pattern as predominantly the consequence of abrasion by relatively small-caliber environmental grit when accidentally ingested with tough foods such as dried seeds and fruits, as expected in a terrestrial omnivore living in a dusty habitat. Statistical analysis revealed no significant differences between groups defined by sex, age, or troop membership, a result consistent with qualitative observations of feeding habits in this population, and which lends no support to the hypothesis that the longer jaws of adult males should result in longer striations. A trend towards greater feature density in females, however, might be due to limited sexual dinichism, and merits further investigation.     

Taste Preference Thresholds for Food-Associated Sugars in Baboons (Papio hamadryas anubis)

We aimed to determine taste preference thresholds for 5 food-associated sugars in Papio hamadryas anubis. In a 2-bottle preference test of brief duration (2 min) 4 subadult baboons significantly preferred concentrations as low as 10 mM sucrose, 20 mM fructose, lactose, and maltose, and 25 mM glucose over tap water. Presentation of suprathreshold sugar solutions led to marked concentration-dependent polydipsia. The results show that baboons are among the most sugar-sensitive nonhuman primates tested so far and, thus, support the assumption that Papio hamadryas anubis may use sweetness as a criterion for food selection.     

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.