Chimpanzees travel by walking on all fours (quadrupedal), using their knuckles to support their body weight. Sometimes, they walk bipedally, upright on two legs. Bipedal walking is less stable because of the angle of the thigh bones in their hip sockets, and it cannot be done for a long time. They spend about the same time traveling through trees (arboreal) and on the ground (terrestrial). They are active only during the day (diurnal) and sleep in groups in nests for the night.

Chimpanzees are considered one of our closest relatives. For years, behavioral studies on chimpanzees have been conducted to better understand human evolution, especially regarding sociality, intelligence, and culture. Chimpanzee behavior has been a subject of many publications because they have been kept in captivity at zoos or research facilities for decades. It is essential to note that many behaviors (e.g., how chimpanzees eat, share meals, and socially interact) depend on the chimpanzee’s environment, so captive behaviors differ significantly from wild chimpanzees. Wild and captive chimpanzees are aggressive and prone to fights, especially between unfamiliar or non-family troops. However, after a fight, wild chimpanzees are unlikely to reconcile or “make peace” with those they fought with. However, in captivity, reconciliatory behavior has been observed, most likely because different groups are forced to live close to each other, and one group cannot move away. Below, we will focus on behaviors commonly seen in wild chimpanzees.

Chimpanzees are one of the great apes that make nests. They mostly build their nests in trees at 36 to 52 feet (11 to 16 m). Nests act as mattresses, usually made from a bed of twigs and branches and softer leaves on top. Once they are weaned from their mother, all chimpanzees gather leaves and materials to build their nests to sleep in at night. New nests are often built every night, and if a nest is re-used, chimpanzees will still add more material to rebuild and modify the old nest. Two or more chimpanzees can join in building individual nests or a shared nest in a “nest party.” Nests can be built at any time of day. Daytime nests are roughly built and used only as a temporary resting site between feeding bouts. Nighttime nests are sturdier and are used to sleep in throughout the night. Nests constructed during the daytime tend to be higher in the trees than those built at night. Adult female chimpanzees tend to build their nests higher than males. Though scientists have not confirmed the reasons for the difference in nest heights between males and females, they have suggested some hypotheses. It may be that males are too heavy to successfully and safely build nests in the higher branches of trees. Males are also the primary protectors of the troop against predators, and building their nests close to the ground where predators like lions may attack is the best strategy for protecting the family.

There is considerable variation in hunting behavior between chimpanzee populations across their range. One hypothesis suggested that chimpanzees hunted and offered meat to females to gain favor during their mating period. However, in some parties, the presence of females in estrus did not increase the number of hunts males participated in, which indicates that males do not exchange hunting favors for mating access. Some studies noted that not every hunting party member received a fair share of the hunt, which suggests that social bonds between males do not necessarily benefit from hunting together. Across populations, chimpanzees are opportunistic hunters even when fruits are abundant. They hunt more in open habitats such as semideciduous forests, where prey are more visible than denser evergreen forests. Ecological factors rather than social ones are better drivers for predicting when chimpanzees hunt.

Tool use has been famously documented in chimpanzee communities, especially ant-dipping, where chimpanzees use a stick to dip into a termite or ant nest to collect the insects to eat. Some field studies have reported advanced tool-set use, where chimpanzees use a branch or rock to break the nest and a stick or stem to scoop the insects out. These multi-step problem-solving techniques are rare abilities in the animal world.

Researchers have also noted that the tools used by chimpanzees differ by region. In some areas, chimpanzees prefer to use different stick lengths to “dip” for different ant species. While in other places, they do not use tools to break the termite or ant nest and only use a stem to dip and pick up ants. Tool use is learned through trial and error and taught from one individual to another. So, a particular technique is learned and passed on to the younger generation of a troop in a specific region. Because female chimpanzees disperse from their natal troop, females likely teach these techniques to troops in other areas. In this manner, tool-use techniques are spread across space. The longer a method is used and the more it is tried in new environments, the higher the probability that the chimpanzee tries and succeeds in improving the tool use or method for their needs.

Learning through watching other members of your community and teaching behaviors to the next generation is the primary step in developing a culture in a community. Culture was once considered a uniquely human characteristic because of our ability to learn and teach each other through social interactions. Chimpanzees also learn socially and can transfer learned behaviors to the next generation. Many researchers accept that these learned behaviors show the development of culture in chimpanzee communities. Chimpanzee behaviors taught across generations include tool use (e.g., what stick lengths are best to get different ant species), gestures, foraging behaviors (what food to avoid or tools to use), and even digging wells for water. These chimpanzee behaviors differ in different communities and regions and point towards cultural diversity in the species. From archeological and historical texts that chronicle observations of chimpanzees, we know that some of these behaviors have persisted for centuries, indicating the evolutionary advantage of maintaining these behaviors.

Grooming is an important part of chimpanzee behavior and life in general. As social animals, transferring pests such as fleas between individuals is common. Grooming is an essential part of maintaining hygiene in the group. The act of grooming is advantageous for both the groomed and the groomer. The groomed gets cleaned, and the groomer gets to snack on any pests they find. There is a social aspect of grooming where kinship between groomer and groomed increases during the behavior. Much like how a mother combing her child’s hair is a sign of love and trust between the two, grooming in primates is also an act of affinity or trust that strengthens the bond between the two individuals. In Mahale, Tanzania, grooming behaviors have developed into cultural behavior where a pair of chimpanzees clasp each other’s hands over their heads and groom each other with their free hand. This behavior is only seen in a few communities and is uncommon for all chimpanzees.

An interesting outcome of social and cultural learning seen in chimpanzees is the unique events of Tanzania’s Gombe National Park. Two chimpanzee communities engaged in a multi-year conflict that many researchers (including the eminent chimpanzee expert Dr. Jane Goodall) compare to the equivalent of war in human culture. This phenomenon is called the “Gombe chimpanzee war” or the “four-year war” that occurred between 1974 and 1978.

The Gombe war was not just the aggressive fights commonly seen among male chimpanzees. Long-term observations of the conflict showed a clear battle for power and resources, similar to human politics. The level of violence sets this conflict apart from the other aggressive fights or hunts seen in the species. Members were ruthless, twisting limbs and bodily harming their victims even after their deaths.

The Gombe War started with the relatively peaceful Kasakela community and the death of a senior male, which led to the community fractioning into the Kasakela and southern Kahama groups. A chimpanzee named “Humphrey” took over the “alpha” role in the Kasakela community, which was highly contested by a pair of brothers named “Hugh” and “Charlie.” The Kasakela community was divided into two groups depending on their allegiance, Humphrey leading the Kasakela group and the brothers leading the southern Kahama group. Neither group socialized with the other and split their space into two territories. On January 7, 1974, six Kasakela males killed a lone southern Kahama male without any provocation. This event triggered a series of vicious killings of males and females in the group of south Kahama by Kasakela members. Over the four years, there was a systematic eradication of all the males of the southern Kahama group and a progressive territorial takeover by the Kasakela group. Surviving southern Kahama females, juveniles, and less dominant males were absorbed into the Kasakela group until only one group emerged victoriously and controlled the entire territory. Researchers were shocked at the violence and domination by members who had essentially played and grown up with their victims. Since the documentation of the Gombe chimpanzee war, researchers have noted similar conflicts in other chimpanzee communities. This phenomenon raises interesting questions about the evolution of warfare in humans and the deep-rooted triggers for violence.