At Kanyawara, we study the East African subspecies of chimpanzee, Pan troglodytes schweinfurthii. The Kanyawara community consists of approximately 60 chimpanzees, and our researchers know each of these individuals by name and face. Read more about some interesting Kanyawara chimpanzees and the roles they play in the community.
Lanjo is a young, adult male in his prime, strong and healthy. A male chimpanzee of his age and condition weighs approximately 80-120 pounds and is several times stronger than an adult human. Since reaching maturity at about age 15, Lanjo increased rapidly in social rank and is a leading competitor for the alpha, or highest-rank, position which was recently vacated by the death of Kakama. Male chimpanzees compete intensely for dominance rank, which gives them various advantages such as better places to feed and increased access to mates. When a high-ranking male like Lanjo encounters other members of his group, he will often perform an impressive display: his hair stands on end (“pilo-erection”) while he charges back and forth, sometimes dragging limbs behind him or drumming on tree buttresses with his feet. Like human leaders, some alpha male chimpanzees lead by brute force, while others play politics, forming valuable alliances with other strong males. Some are very successful, staying dominant for many years and siring many offspring with females, while others are quickly deposed. We are currently researching the costs and benefits of high rank, individual variation in the use of aggression, and the formation and maintenance of coalitions among male chimpanzees.
Unlike Lanjo, young Max has not managed to attain high rank in the community. Perhaps this is because he is smaller in size and lost both of his feet to wire snares when he was a juvenile, limiting his ability to compete. Max’s mother is one of our peripheral females, meaning that she ranges in the border areas of the home range and is not very social with other chimpanzees, preferring to range alone. Such habits limited Max’s opportunities to engage with mature males as he was growing up and likely exposed him to areas frequented by hunters.
In chimpanzees, males remain in their mothers’ groups throughout their lives and form close relationships with the other males. These relationships facilitate cooperation in behaviors such as hunting for monkeys and guarding their home range from chimpanzees in other communities. The Kanyawara chimpanzees range through over 30 square kilometers of forest, and at any given time they are scattered in various smaller groups (“parties”) that forage or travel together temporarily. This is called “fission-fusion” social organization. Some individuals, especially mothers, may chose to feed alone much of the time to avoid competing with others. Many of our studies focus on what factors determine the size of chimpanzee parties, how individuals vary in their gregariousness, and what leads some pairs of chimpanzees to associate more than others. Our conservation efforts attempt to help prevent injuries like Max’s (see Conservation). Increase funding for our snare removal program has allowed us to expand the area patrolled for hunting and other illegal activities.
Outamba is a very successful mother in her early thirties. She was first seen in 1992 when she immigrated into the Kanyawara community. Since then, she has given birth to 5 offspring. Chimpanzees reproduce very slowly, usually with about 5-8 years between successive births. Outamba’s births have been only 3-4 years apart. We are discovering that this may have to do with her access to food resources. Within the community of chimpanzees, females establish their own smaller feeding ranges which can vary significantly in quality — females like Outamba who live in the best areas produce more ovarian hormones, have higher birth rates, and have infants who are more likely to survive. Given a reproductive lifespan that can extend well over 30 years, range quality has a significant impact on lifetime reproductive success. Dominance rank relationships among female chimpanzees are more difficult to assess than among males because females do not associate with one another as frequently and try to avoid conflicts which may threaten their infant’s safety or their ability to get food. However, it is clear that Outamba is the highest ranking female at Kanyawara. Our longitudinal studies will also help us examine how Outamba’s high rank and foraging success impacts her offspring’s development and eventual success as adults.
Quinto is a recent immigrant into the Kanyawara community. Females typically transfer between communities when they reach sexual maturity. This likely functions to help females avoid mating with fathers and brothers in their natal communities. At approximately 10-12 years of age, females begin to experience large swellings of their genital skin that accompany ovarian cycles. These swellings are very attractive to males and may act as a “passport” to allow females like Quinto to move into a new community. While males may welcome these new females, resident females are very aggressive, forming coalitions to exclude new females from their feeding areas. Immigrants experience increased stress and associate closely with males to avoid aggression from other females. We are studying the costs and benefits of female immigration, hormonal and behavioral correlates of female transfer, and what strategies may allow some immigrants to fare better than others.
Ipassa and Tuke
Ipassa and Tuke are adolescent chimpanzees entering the critical period of puberty. As a female, Ipassa will soon begin experiencing sexual cycles and will receive increasing amounts of sexual attention from males. Tuke must begin forming relationships with the adult males of the community. Tuke will soon outgrow and dominate all the females in the community. Even while still small, Tuke is starting to practice displaying and spends much of his free time harassing females smaller than himself. While finding his way in the politics of the chimpanzee community are essential for Tuke’s future success, Ipassa’s objectives are to find the best place for her and her future offspring to forage. We are currently investigating the ontogeny of sex differences in behavior of chimpanzees.
Gola is a young infant in the community, born to Outamba, the alpha female in the community. Chimpanzee infants are born more well-developed than are human infants — they must cling to their mothers in the trees! Gola’s mother will provide milk for him for 2-4 years, but gradually Gola will venture away from her mother’s embrace for longer and longer periods, exploring her environment, learning what there is to eat (and how to eat it), and playing with other juveniles and adults. Recently, we discovered that young chimpanzees like to use sticks from the forest as toys, carrying a favorite stick around for long periods. They show a remarkable sex difference in how they use them. Girls like Gola carry their sticks close to them and even build sleeping nests to place their sticks in. Boy chimpanzees are more likely to poke or hit other chimpanzees with their sticks.