Strong male bonds are rare among primates, especially for female-bonded species. Thus, the relationship between male bonding and reproductive strategies remains largely unexamined in female-bonded species. Geladas (Theropithecus gelada) provide an ideal model for understanding how male bonds influence male reproductive trajectories in a female-bonded species. Prior to acquiring reproductive access to females, "bachelor" geladas live in cohesive all-male groups. Eventually, males graduate from these groups to gain sole reproductive access to a group of females (one-male unit). Bachelors acquire one-male units using one of several strategies: (1) directly overthrowing the leader male, (2) submissively entering a unit and attempting to pare females away from the unit over time, or (3) capitalizing on the chaos of a recent takeover to opportunistically mate with females. Additionally, bachelors have been observed to cooperate in attempts to overthrow leader males and enter one-male units with former members of their all-male group - yet only one male eventually reaps the reproductive benefits. This project investigates the behavioral and hormonal factors that shape the reproductive trajectory of gelada males as they move from an all-male group to a one-male unit. The researchers will(i) describe the social interactions among bachelors within their all-male group; (ii) determine the behavioral and hormonal factors that influence bachelor participation in takeover attempts of leader males, and (iii) determine whether bachelor quality predicts a reproductive strategy. Behavioral data and noninvasive fecal hormone sampling will document the reproductive trajectories of male geladas. Additionally, digital photographs will be taken of male chest patch color - a feature that may indicate male quality - to document changes in color as males move from their bachelor groups to one-male units.
Results from this research will inform conservation decisions regarding these rare primates, and the investigator's presence in the Simien Mountains National Park help deter illegal activities in this World Heritage Site that is in danger. This project provides income and training to local Ethiopian field assistants and the co-PI has arranged to explain gelada behavior to high school students in several U.S. states.
Our project investigates the behavioral and hormonal factors that influence social bonding and reproductive trajectories of male geladas. Geladas are a rare primate species that are closely related to the common baboon. While baboons are found across all of Africa, geladas are restricted to the grassy highlands of Ethiopia where they live in social groups of over 1000 individuals. These groups are among the largest gatherings of nonhuman primates anywhere in the world. Gelada "herds" are comprised of many smaller, closed social units. In these social units, several related females live with one dominant "leader" male. The leader male monopolizes all reproductive opportunities with his associated females. Before they can become leaders, young gelada males live in bachelor groups with each other and form strong "friendships" with one another. But why do these bachelors invest in such relationships if only one male can become a leader? This project combines field-based observations of wild geladas in Ethiopia with lab procedures for hormone analysis at the University of Michigan. We have discovered that bachelor geladas form friendships with each other in order to cope with ecological and psychological stressors. Chronic stress in humans and other animals has been linked to numerous diseases and can suppress the immune system. Bachelor geladas live in an extremely stressful environment for a primate. Temperatures regularly dip below freezing in the Ethiopian mountains, and leader males constantly harass bachelors that try to approach their females. Bachelors that forge the strongest friendships with each other have the lowest stress levels. In other words, bachelors develop friendships for health benefits. This is one of the first studies to demonstrate a relationship between stress and social bonding among males in a wild primate. We have also worked closely with other researchers to determine if bachelor geladas are forming friendships with family members. Since we don’t know if any two males are related to each other, we have to noninvasively extract genetic material in order to determine kinship. We have discovered that while bachelor geladas often live with close kin, their strongest friendships are with unrelated individuals. This is similar to findings in male chimpanzees and humans. Overall, we suggest that friendships among male geladas are an adaptive strategy to cope with a stressful environment. We have engaged in several public outreach projects both in Ethiopia and the United States. Our project employs three Ethiopian nationals as research assistants and six full-time park scouts. In Ethiopia, we have spoken to tourists and locals about conserving Ethiopian biodiversity and protecting the fragile environment of the Simien Mountains—the gelada’s home and a UNESCO World Heritage Site. In April 2011, we spoke about our research with over 500 high school students at Addis Ababa University during the "Yes Youth Can!" conference. In the United States, we have given invited talks on our research at the University of Michigan and the University of Pennsylvania. We have also trained undergraduate students in various lab-based methods of data analysis. We provide regular updates on our research to an internet-based audience on our website and blogs. Through these outreach activities, we hope to inspire a generation of eco-minded citizens and future scientists.
