The Filoha Hamadryas Project began in 1996-1998 with Larissa Swedell's Ph.D. research focusing on hamadryas baboon behavioral ecology (Swedell 2002b) and the reproductive and social strategies of females (Swedell 2000, 2002a, 2006). Subsequently, ongoing research and analyses have focused on demography, reproduction, and reproductive strategies (Swedell & Tesfaye 2003; Swedell & Saunders 2006), vocalizations (Saunders, in prep), and feeding ecology (Swedell et al, in press). In addition to these ongoing foci of the project, the following sub-projects have been recently completed or are underway at the present time:

Resource Distribution, Social Structure, and Travel Patterns

PIs: Amy Schreier (Ph.D., CUNY, 2009) and Larissa Swedell

Hamadryas baboons are well-known for the flexible, multi-level social structure distinguishing them from other members of the genus Papio. The evolution of this social structure has often been attributed to the scarce and widely dispersed distribution of resources in hamadryas habitats, but such an association between food availability and social structure in hamadryas baboons has never been quantitatively shown. Additionally, several studies suggest that hamadryas baboons use their home range unevenly, corresponding to the location of important resources, and travel as if they have knowledge of the spatial layout of their environment. This project involved a quantification of the distribution and abundance of resources in the home range of Band 1 at Filoha, over space and time, as well as a systematic investigation of the relationship between resource availability and changes in the baboons' multilevel social structure, home range use, and travel patterns.

Schreier, A. & Swedell, L. (2007) Evidence for Clans in a Population of Wild Hamadryas Baboons. American Journal of Physical Anthropology Supplement 44: 209-210 (abstract).

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.

Variation in Female Social Lives in a Male-Dominated Society: Bonds, Stress and Reproduction in Female Hamadryas Baboons

PIs: Shahrina Chowdhury (Ph.D. Candidate, CUNY) and Larissa Swedell

This project follows up on Swedell's earlier (2002a, 2006) work on social and sexual strategies of hamadryas females by focusing on the relationship between social bonds, stress, and reproduction in female baboons. Hamadryas society is among the most male-dominated among primates. One-male units (OMUs) are controlled by 'leader males', who take over females from other males and physically coerce them into these social units. Hamadryas females thus receive a substantial amount of aggression from leader males, especially during and after takeovers, and this aggression also sometimes leads to infant mortality. Female hamadryas have also been reported to focus most of their social interactions towards their leader males while forgoing close social ties with other females in their unit. This combination of aggression from males, lack of close social ties with other females, and risk of infanticide from takeovers might be expected to result in higher stress and reduced fitness of hamadryas females compared to other baboons. On the other hand, the hamadryas social system may actually benefit females in that offspring survival is enhanced by protection from leader males, a possibility that is conceivable because hamadryas infants have higher survival rates compared to other baboons. Moreover, recent studies have revealed that social interactions among females within an OMU are more important than previously thought. This is important because it has been found in other baboons that female social bonds improve fitness, and this may be the case for hamadryas as well. Stress associated with such a male-dominated society may thus be counter-balanced by coping mechanisms and social bonds of females. In this project, we aim to study variation in the behavioral strategies of females across OMUs of varying size and composition. Using proximate measures of fitness, such as short-term reproductive parameters and stress levels as measured by glucocorticoid hormones and self-directed behavior, we will determine whether female fitness differs depending on the strength and quality of social relationships with other unit members and if females in fact exercise strategies to cope with their specific social environment. Currently funded by a National Science Foundation Doctoral Dissertation Improvement Grant to Shahrina Chowdhury and Larissa Swedell

Brothers in Arms or Rivals in Waiting? The Role of Follower Males in Hamadryas Social Organization

PIs: Larissa Swedell, Julian Saunders, and Mathew Pines

Hamadryas baboons are unique among primates in having a multi-tiered society in which leader males aggressively herd females into semi-permanent one-male units (OMUs). OMUs coalesce into larger groupings called clans, associations of several OMUs and solitary males that are possibly linked by male kinship, and bands, associations of two or more clans that travel and sleep together. Also present in bands but not associated with individual OMUs are solitary males, who move throughout the band and interact with other solitary males and juveniles. Some OMUs also include one or more follower males, who consistently associate with a particular OMU. Within this system, it seems fairly certain that most males eventually gain females and become leaders; however, it is not clear why, on the path to that role, some males become solitary and others become followers. It is also unclear why leader males tolerate followers in their OMUs. Whether leaders and followers are close relatives is not known, though it has been speculated that they are half siblings and that they both benefit from this relationship via inclusive fitness (e.g., Kummer 1968). This project aims to address the following central question: What is the role of follower males in hamadryas baboon social organization? Using behavioral, genetic, and hormonal data, we will (1) document the life history trajectory of males before, during, and after they are follower males, (2) characterize the leader-follower relationship, (3) determine the explanatory paradigm behind the dichotomy between solitary and follower males and the relative costs and benefits of each, and (4) assess why leader males tolerate the presence of follower males in their OMUs. The genetic labwork for this project will be conducted in collaboration with Linda Vigilant (Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany) Leipzig, Germany, and the hormone labwork will be conducted in collaboration with Jacinta Beehner (Department of Anthropology, University of Michigan, Ann Arbor, MI, USA). Currently funded by grants from the Leakey Foundation and the National Geographic Society.

Swedell, L., Saunders, J., Pines, M., Schreier, A., & Davis, B. (2008) Alternative Reproductive Strategies in Male Hamadryas Baboons: Leaders, Followers, and Solitary Males. American Journal of Physical Anthropology Supplement 46: 203 (abstract).