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

Previous studies of hamadryas baboons have described a “star-shaped” sociogram, whereby the strongest social bonds within hamadryas one-male units are those between a leader male and his females and bonds among females are weak by comparison. This type of social organization has also been called “cross bonding” to distinguish it from the “female bonding” found in most papionin monkeys. Models of female primate socioecology have suggested 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 their 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 negatively correlated with the tendency of its females to interact with their leader male. Females were equally likely to spend social time with other females whether or not their leader male was available for social interaction at the time. Overall, this study suggests that a star-shaped sociogram does not necessarily 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

Patterns of reconciliation among captive gelada baboons (Theropithecus gelada)

Animals that live in groups are frequently exposed to conflict situations and must in some way maintain group cohesion. One mechanism that appears to restore social relationships after they have been disrupted by conflict is reconciliation. This study investigated reconciliatory behavior in the gelada baboon, Theropithecus gelada. The subjects were 11 adult geladas, housed in a large outdoor enclosure at the Bronx Zoo/Wildlife Conservation Park, New York. Five-minute focal animal samples following spontaneous aggression were compared with 5-min matched-control samples. The results of this study were: (1) geladas reunited in a friendly way after aggression; (2) former opponents were attracted to one another rather than dispersed from one another after a conflict; (3) most post-conflict reunions occurred within the first 2 rain of the post-conflict period; and (4) geladas do not have any specific types of behavior associated with post-conflict reunions as do chimpanzees and macaques. The results of this study support the hypothesis that gelada baboons reconcile after aggression

Ranging Behavior, Group Size, and Behavioral Flexibility in Ethiopian Hamadryas Baboons (Papio hamadryas hamadryas).

This study reports group size, home range size, daily path lengths, seasonal effects on ranging behavior and qualitative information on diet for a population of hamadryas baboons inhabiting the lowlands of the northern Rift Valley in central Ethiopia. The minimum home range size and daily path length for this population are similar to those reported for other populations of hamadryas baboons in Ethiopia and Saudi Arabia. Group sizes, however, are much larger than those in most other hamadryas populations for which published data are available. The large group sizes in this area may be related to the abundance of one food resource in particular, doum palm nuts. Overall, this study suggests that hamadryas baboons may be more flexible in some aspects of their behavioral ecology (e.g. group size) than in others (e.g. ranging behavior)

Two Takeovers in Wild Hamadryas Baboons

Hamadryas baboons exhibit a multi-level social structure in which several one-male units, each consisting of a ‘leader’ male and one or more females, comprise a band’ and two or more bands comprise a troop. Cohesion of each one-male unit is maintained by aggressive herding by its leader male [1]. Here I describe the consequences of 2 takeovers in a band of wild hamadryas baboons. I report evidence of infant mortality following takeovers, changes in female reproductive condition within 2 weeks after takeovers, and the reacquisition of a female by a deposed leader male, none of which has been previously reported for wild hamadryas baboons

Infant Mortality after Takeovers in Wild Ethiopian Hamadryas Baboons

In this paper, 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 1200 hours, 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 eleven days of the takeover. After the second takeover, the infant incurred repeated severe aggression from its mother’s new leader male and eventually died four days after the takeover. We interpret these findings as support for the sexual selection hypothesis for the occurrence of 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

Use of Palm Trees as a Sleeping Site by Hamadryas Baboons in Ethiopia

Hamadryas baboons sleep on cliffs throughout their range, and this can be attributed to the safety cliffs provide against predators in the absence of tall trees. In this paper, we report the first documented occurrence of hamadryas baboons sleeping in doum palm trees rather than on cliffs. Data derive from a study of hamadryas baboons at the Filoha site in lowland Ethiopia. During all-day follows, data were collected on travel patterns, band activity, and location. Variation in the baboons’ home range was characterized using vegetation transects. We discovered that one band in this population, Band 3, occasionally slept in doum palm trees (Hyphaene thebaica). The palm tree sleeping site differed from other palm fragments in the baboons’ home range in that it contained a higher density of palm trees. Possible factors influencing this unique use of palm trees as a sleeping site include access to palm fruit, avoiding contact with Afar nomads, avoiding sharing sleeping cliffs with other bands, protection from predators, and the lack of cliffs in a section of the baboons’ home range. Evidence from this study suggests that the palm tree sleeping site is used because it affords better protection from predators than other palm fragments in an area of the band’s home range that does not contain cliffs

Composition and Seasonality of Diet in Wild Hamadryas Baboons: Preliminary Findings from Filoha

Here we report the first year-round quantitative data on dietary composition and seasonality in wild hamadryas baboons. Study subjects were adult male members of Band 3 at the Filoha field site in central lowland Ethiopia. Data collection consisted of 10-minute focal samples during all-day follows 4-6 days per month over the course of one year. The two largest contributors to the diet were Hyphaene thebaica and Acacia senegal, and these were the only plant species found in the diet during every month of the year. Other relatively major contributors to the diet, such as Cyperus grandibulbosus, Seddera bagshawei, Tribulus cistoides and Typha latifolia, showed a seasonal pattern. Fewer plant species were consumed during the dry months of the year compared to the wet months. During the hottest and driest months of the year, study subjects subsisted almost exclusively on Hyphaene thebaica, Acacia senegal, Cyperus grandibulbosus,and Typha latifolia. Overall, these patterns suggest that this population of hamadryas baboons spends less time feeding and is able to subsist on a narrower array of plant foods compared to other baboons. This pattern may be driven by the presence at Filoha of the doum palm (Hyphaene thebaica), a high-quality food resource that is consumed year-round