Alternative Routes to the Leader Male Role in a Multi-level Society: Follower Versus Solitary Male Strategies and Outcomes in Hamadryas Baboons

Pines, M., Saunders, J., & Swedell, L. (2011) Alternative Routes to the Leader Male Role: Follower versus Solitary Male Strategies and Outcomes in Hamadryas Baboons. American Journal of Primatology 73: 679-691.

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 pre-reproductive 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 derive from 42 OMU formations (16 by followers and 26 by solitary males) occurring over eight years in a hamadryas baboon band at the Filoha site in Ethiopia. “Initial units” 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 two years as a leader. These results demonstrate the potential for males to employ both multiple roles (follower versus solitary male) and multiple routes (initial unit, inheritance, challenge, opportunistic) to acquire females and become a leader male in a mating system characterized by female defense polygyny in a competitive arena.

Not Without a Fair Fight: Failed Abductions of Females in Wild Hamadryas Baboons

Pines, M. & Swedell, L. (2011) Not without a Fair Fight: Failed Abductions of Females in Wild Hamadryas Baboons. Primates, in press.

In contrast to other papionin monkeys, hamadryas baboons are characterized by female-biased dispersal. Given that hamadryas females do not disperse voluntarily, one mechanism for female transfer between bands is thought to be abductions of females during aggressive intergroup conflict. To date, however, no successful abductions have been witnessed. We describe three abduction events at the Filoha field site in Ethiopia, two inter-band and one intra-band, in which the abductors successfully separated a female from her leader male for several minutes or hours. In each case, the original leader male located the abductor and retrieved the female, even if it involved entering the social sphere of another band. These observations suggest that a hamadryas leader male will risk injury and loss of additional females in his attempt to retrieve a female from an abductor unless the abductor has openly challenged the leader for possession of his female and physically defeated him.

Female “Dispersal” in Hamadryas Baboons: Transfer among Social Units in a Multi-Level Society

Swedell, L., Saunders, J., Schreier, A., Davis, B., Tesfaye, T., & Pines, M. (2011) Female “Dispersal” in Hamadryas Baboons: Transfer among Social Units in a Multi-Level Society. American Journal of Physical Anthropology 145: 360-370.

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 seven years of data on female transfers among social units in wild hamadryas baboons in Ethiopia. Female tenure in one-male units (OMUs) ranged from one to 2556 days (N=208) and survival analysis revealed a median tenure length of 1217 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.

African Papionins: Diversity of Social Organization and Ecological Flexibility

Swedell, L. (2011) African Papionins: Diversity of Social Organization and Ecological Flexibility. IN Primates in Perspective, Second Edition, edited by C. Campbell, A. Fuentes, K. MacKinnon, S. Bearder, & R. Stumpf. New York: Oxford University Press, pp. 241-277. (released April 2010)

from Oxford University Press website:

Description
Featuring forty-seven original essays by seventy leading researchers, Primates in Perspective , Second Edition, offers a comprehensive and contemporary overview of all major areas of primatology. Thoroughly revised and updated throughout, the second edition offers a diversity of theoretical positions on such topics as reproduction, ecology, and social behavior and intelligence.

Primates in Perspective , Second Edition, is ideal for introductory primatology courses and can also be used in upper-division behavior and conservation courses. Additionally, it is an essential reference for primate researchers.
Features

* New chapters on baboons, mandrills, and mangabeys; behavioral methods; ecological methods; juveniles and adolescents; kinship; and tool use
* A 16-page insert that features more than 30 full-color photos of primates
* More than 50 new maps and figures
* A glossary at the back of the text clearly defines new terms for students
* Reading questions at the beginning of each chapter guide students to big-picture concepts and serve as discussion starters and assignment prompts
* A "How to Use This Book" section offers tips on teaching from the text
* An extensive, up-to-date bibliography at the back of the text

Product Details
864 pages; 8-1/2 x 11; ISBN13: 978-0-19-539043-8ISBN10: 0-19-539043-1

The Effects of Extreme Seasonality of Climate and Day Length on the Activity Budget and Diet of Semi-commensal Chacma Baboons (Papio ursinus) in the Cape Peninsula of South Africa

van Doorn, A., O’Riain, M.J., & Swedell, L. (2010) The effects of extreme seasonality of climate and day length on the activity budget and diet of semi-commensal chacma baboons (Papio ursinus) in the Cape Peninsula of South Africa. American Journal of Primatology 72(2): 104-112.

We examined the effects of extreme seasonality on the activity budget and diet of wild chacma baboons with access to a high quality human-derived food source. The Cape Peninsula of South Africa is unusual among nonhuman primate habitats due to its seasonal extremes in day length and climate. Winter days are markedly shorter and colder than summer days but have higher rainfall and higher primary production of annually flowering plants. This combination of fewer daylight hours but higher rainfall is markedly different from the ecological constraints faced by both equatorial baboon populations and those living in temperate climates with summer rainfall. We sought to understand how these seasonal differences affect time budgets of food enhanced troops in comparison to both other food enhanced troops and to wild-foraging troops at similar latitudes. Our results revealed significant seasonal differences in activity budget and diet, a finding that contrasts with other baboon populations with access to high return anthropogenic foods. Similar to non-provisioned troops at similar latitudes, troop members spent more time feeding, socializing and traveling during the long summer days compared to the short winter days, and proportionately more time feeding and less time resting in summer compared to winter. Summer diets consisted mainly of fynbos and non-indigenous foods, whereas winter diets were dominated by annually flowering plants (mainly grasses) and ostrich pellets raided from a nearby ostrich farm.. In this case, food enhancement may have effectively exaggerated seasonal differences in activity budgets by providing access to a high return food (ostrich pellets) that was spatially and temporally coincident with abundant winter fallback foods (grasses). The frequent use of both alien vegetation and high return human-derived foods highlights the dietary flexibility of baboons as a key element of their overall success in rapidly transforming environments such as the South African Cape Peninsula.

Male Aggression Toward Females In Hamadryas Baboons: Conditioning, Coercion, and Control

Swedell, L. & Schreier, A. (2009) Male Aggression Towards Females in Hamadryas Baboons: Conditioning, Coercion, and Control. IN Sexual Coercion in Primates: An Evolutionary Perspective on Male Aggression Against Females, edited by M. Muller and R. Wrangham. Cambridge: Harvard University Press, pp. 244-268.

from Harvard University Press website:

Conflict between males and females over reproduction is ubiquitous in nature due to fundamental differences between the sexes in reproductive rates and investment in offspring. In only a few species, however, do males strategically employ violence to control female sexuality. Why are so many of these primates? Why are females routinely abused in some species, but never in others? And can the study of such unpleasant behavior by our closest relatives help us to understand the evolution of men’s violence against women?

In the first systematic attempt to assess and understand primate male aggression as an expression of sexual conflict, the contributors to this volume consider coercion in direct and indirect forms: direct, in overcoming female resistance to mating; indirect, in decreasing the chance the female will mate with other males. The book presents extensive field research and analysis to evaluate the form of sexual coercion in a range of species—including all of the great apes and humans—and to clarify its role in shaping social relationships among males, among females, and between the sexes.

The Fourth Level of Social Structure In a Multi‐level Society: Ecological and Social Functions of Clans In Hamadryas Baboons

Schreier, A. & Swedell, L. (2009) The Fourth Level of Social Structure in a Multi-Level Society: Ecological and Social Functions of Clans in Hamadryas Baboons. American Journal of Primatology 71: 948-955.

Hamadryas baboons are known for their complex, multi-level social structure consisting of troops, bands, and one-male units (OMUs) [Kummer, 1968]. Abegglen [1984] observed a 4th 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 2 observation periods this band comprised 2 large clans ranging in size from 7 to 13 OMUs. All band fissions occurred along clan lines, and most takeovers involved 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.

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

Swedell, L., Hailemeskel, G., & Schreier, A. (2008) Composition and Seasonality of Diet in Wild Hamadryas Baboons: Preliminary Findings from Filoha. Folia Primatologica 79: 476-490.

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.

Use of palm trees as a sleeping site for hamadryas baboons (Papio hamadryas hamadryas) in Ethiopia

Schreier, A. & Swedell, L. (2008) Use of Palm Trees as a Sleeping Site by Hamadryas Baboons in Ethiopia. American Journal of Primatology 70: 107-113.

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.

Perspectives on Reproduction and Life History in Baboons

Swedell, L. & Leigh, S. (2006) Perspectives on Reproduction and Life History in Baboons. IN Reproduction and Fitness in Baboons: Behavioral, Ecological, and Life History Perspectives, edited by L. Swedell & S. Leigh. New York: Springer, pp. 1-15. (Introductory chapter to edited volume)

This volume brings together current research on the behavior, ecology, reproduction, and life history – and the interrelations among these variables – of baboons of the genus Papio. Baboons, found throughout Africa and into Arabia, represent one of the best-known primate lineages, renowned for their ecological and behavioral flexibility and adaptability. These characteristics are intimately intertwined with features of baboon life history and reproduction. Contributors to this volume, representing several major, long-term research projects from throughout the African continent, explore reproductive behavior and strategies of adult male and female baboons in a variety of ways. In Part I, authors explore various aspects of baboon reproduction and social organization, focusing on issues such as infanticide, mating strategies and investment, hybridization and genetics in examining how adults go about mating and reproducing. In Part II, these aspects of life are juxtaposed with detailed examinations of life history and parental investment. Together, the chapters in this volume explore reproduction and parenting from a variety of angles and motivate research from both the parental and offspring perspectives and at a variety of taxonomic levels. Articulating studies of reproduction with those of life history conveys a richly detailed portrait of life phases with critical evolutionary consequences. These lines of inquiry together forge new ways to investigate the life periods that matter most in evolution.

Infant Mortality, Paternity Certainty, and Female Reproductive Strategies in Hamadryas Baboons

Swedell, L. & Saunders, J. (2006) Infant Mortality, Paternity Certainty, and Female Reproductive Strategies in Hamadryas Baboons. IN Reproduction and Fitness in Baboons: Behavioral, Ecological, and Life History Perspectives, edited by L. Swedell & S. Leigh. New York: Springer, pp. 19-51.

In this chapter, we compare female behavior in hamadryas baboons to that of other baboon subspecies as a means to elucidate female baboon reproductive strategies. Hamadryas differ from other Papio baboons in that their social organization centers around reproductively exclusive one-male units. Infanticide and aggression towards infants are risks for hamadryas and other baboons and, as has been suggested for other primates, these risks may have played a primary role in shaping female baboon reproductive strategies. One way that females may guard against aggression towards infants is by increasing paternity uncertainty through promiscuity and the incitement of male contest and sperm competition. Presentations to multiple males, post-copulation darts, and copulation calling in particular have been suggested as mechanisms whereby females may incite male competition at both the pre- and post-copulatory levels. Accordingly, a coupling of infanticide risk and multiple mating by females (and the associated male competition) characterizes many baboon societies. Another, alternate route to ensure protection against infanticide and other forms of infant mortality is association and exclusive copulation with a single protective male. This strategy characterizes hamadryas baboon females. Paternity certainty is probably quite high among hamadryas leader males, and protective behavior towards infants has likely been selected for. Correspondingly, compared to other baboons, female hamadryas are less promiscuous, do not frequently initiate copulation, and rarely behave in ways that might incite male-male competition. We suggest that, while all baboon females use a combination of paternity concentration and confusion, hamadryas baboon females in particular focus on paternity concentration rather than confusion and that this can be explained by changes in male and female reproductive strategies during the evolution of hamadryas social organization.

Ranging Behavior, Group Size and Behavioral Flexibility In Ethiopian Hamadryas Baboons

Swedell, L. (2002b) Ranging Behavior, Group Size, and Behavioral Flexibility in Ethiopian Hamadryas Baboons (Papio hamadryas hamadryas). Folia Primatologica 73:95-103.

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 in Ethiopia and Saudi Arabia. Group sizes at Filoha, 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 may be more flexible in some aspects of their behavioral ecology (e.g., group size) than in others (e.g., ranging behavior).

Affiliation among females in wild hamadryas baboons (Papio hamadryas hamadryas)

Swedell, L. (2002a) Affiliation Among Females in Wild Hamadryas Baboons (Papio hamadryas hamadryas). International Journal of Primatology 23: 1205-1226.

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.

Infant mortality after takeovers in wild Ethiopian hamadryas baboons

Swedell, L. & Tesfaye, T. (2003) Infant Mortality After Takeovers in Wild Ethiopian Hamadryas Baboons. American Journal of Primatology 60: 113-118.

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.

Two takeovers in wild hamadryas baboons

Swedell, L. (2000) Two Takeovers in Wild Hamadryas Baboons. Folia Primatologica 71: 169-172.

Introduction:

Hamadryas baboons exhibit a multi-level social structure in which several one-male units (OMU’s), 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 OMU is maintained by aggressive herding by its leader male.

Here I describe the consequences of two takeovers in a band of wild hamadryas baboons. I report evidence of infant mortality following takeovers, changes in female reproductive condition within two 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.

Patterns of reconciliation among captive gelada baboons (Theropithecus gelada): a brief report

Swedell, L. (1997) Patterns of Reconciliation Among Captive Gelada Baboons (Theropithecus gelada). Primates 38(3): 327-332.

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.

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