Meet Kanyawara Chimpanzees

At 23 years old, Kakama is an 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, Kakama has risen rapidly in social rank and is now challenging for the alpha, or highest-rank, position. 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 Kakama 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. Unlike the alpha male he is challenging, Kakama is a relatively gentle chimpanzee, rarely engaging in the severe hiting, biting, and kicking that so many male chimpanzees use to intimidate rivals and potential sexual partners. Our researchers often see Kakama running to comfort and embrace a female who has been attacked by another male. We are currently researching individual variation in aggressive tendencies and what factors might lead a male like Kakama to be successful.

Unlike Kakama, 20-year old Twig has not managed to attain high rank in the community. Perhaps this is because he is smaller in size and lost his right hand to a snare when he was a juvenile, limiting his ability to compete. Twig's mother was also missing a hand and perhaps as a result was not very social with other chimpanzees, preferring to range alone. This may have limited Twig's opportunities to engage with mature males as he was growing up.

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.

Outamba is a very successful mother in her late twenties. She was first seen in 1992 when she immigrated into the Kanyawara community. Since then, she has given birth to 4 offspring (largest to smallest: Kilimi, Tenkere, Tacugama, infant Omusisa not pictured). 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. 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. Chimpanzees are rare among primates in that females typically transfer communities at 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 Eslom are adolescent chimpanzees entering the critical period of puberty, unfortunately both with recently deceased mothers. As a female, Ipassa will soon begin experiencing sexual cycles and will receive increasing amounts of sexual attention from males. Eslom must begin forming relationships with the adult males of the community. Eslom will soon outgrow and dominate all the females in the community. Even while still small, Eslom 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 Eslom'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.