Social Organization
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Communities
The highest order of social organization among chimpanzees is their community. The size of a community typically ranges from 40 to 60 members, but can fluctuate drastically depending on the area (Goodall, 2001). Within these larger communities is a great deal of different types of social groupings.
Photo Courtesy of Jane Goodall Institute
Fusion-Fission Groups
The groups within the communities are known as fusion-fission groups because the membership is fluid and usually changing. The party sizes change regularly according to three factors: 1. environmental and demographic factors, 2. variation in the number of females in estrus, and 3. social factors, including dominance shifts or the introduction of new chimps into their territories. Chimps travel in parties of up to five members, and the composition of these parties may include the following: all-male parties, family units, nursery units (consisting of two or more family units), mixed parties (one or more male or adolescent males with one or more adolescent females), sexual parties (one or more females in estrus and males), consortships (exclusive relationship between one adult male and one adult female who may or may not be in estrus), gatherings (comprised of at least half of the community members, and usually existing as a large, mixed, sexual group), and lone individuals. The group make-up is contingent on the food supply; they tend to travel in larger groups when food is more plentiful (Goodall, 1986).
Differences Between Males and Females
Males are more gregarious than females and tend to spend more of their time with other males, unless a female is in estrus. Females who are not in estrus tend to spend their time independent from other chimps with the exception of their own offspring. Companionship for females comes almost exclusively from family bonds; her bonds with her adolescent and adult daughters are especially strong. Males, on the other hand, will more frequently associate with members outside of the family group (Goodall, 1986)
Sex differences also seem to influence the social structure of chimpanzees.
Males usually remain in natal groups, cooperate in defense of the community
range, and spend long periods of time in proximity to other males. Adult
male-male interactions are reportedly more common than other interactions
between individuals. Grooming among males has also been observed more than
grooming among females. Males are observably more affected by the presence
of others during feeding, and as a result they tend to feed less than females
while in a group. Females on the other hand disperse from the natal group
and spend most of their time alone of with dependent offspring. For reproductive
reasons, food intake may be more important to females; their less sociable
nature may result from their attempts to reduce feeding competition and intake
food intake (Brent, et al., 1993).
Male and Female Interactions
The nature of male-female social interactions is contingent on the estrus state of the female. For instance, males spend more time around females who are in estrus. Bisexual parties are considered reproductive groupings. These usually consist of the alpha male and many other males as well as cycling females. The difference in gregariousness in males and females may be due to the heightened importance of foraging on female’s reproductive success. While females not in estrus spend most of their time looking for food alone, males spend their time in social situations trying to attract females in estrus. Female behavior seems to depend most on whether they are cycling or noncycling. If they are cycling, their behavior is then also contingent on whether they are in estrus or not. Noncycling females tend to be the least social so as to conserve physical strength and maximize their energy. Females both in and out of estrus will join bisexual parties, but only those in estrus seem to increase in gregariousness (Matsumoto-Oda, 1999). Adult males usually dominate all females, but competition is so rare that this relationship probably does not affect feeding (Brent, et al., 1993)
Dominance Hierarchies
Age is a deciding factor in male dominance hierarchies. The alpha male is usually between the age of twenty and twenty-six. Other factors that determine dominance are physical fitness, aggressiveness, skill at fighting, ability to form coalitions, intelligence, and other personality factors. The charging display is the main way males work their way up in the hierarchy and also maintain his position. Males will sometimes fight to try and maintain their rank. These fights sometimes, but not usually, result in the death of the loser. Sometimes fights involve a “hit and run” technique where a younger male will strike or slap at an older, higher ranking male in passing. The continuation of such behavior may boost the younger male’s confidence enough so that he one day decides to initiate a more serious attack. This type of fighting is more serious and may result in the permanent reversal of rank between two males. Males will sometimes form coalitions with each other to enlist support during conflicts with other males. Stable coalitions are based on long-term friendships, while opportunistic coalitions consist of two or more males who temporarily join forces against a common adversary (Goodall, 1986).
Females also have some sort of confused dominance hierarchy. The more ambiguous
nature of their system probably has to do with they hardly spend time together
in the first place. Usually one female is clearly the high-ranking female,
and others are clearly the lower ranking individuals. The high-ranking female
also has a high display rate, like the males. Charging behaviors are common
for these females as well (Goodall, 1986).
Aggression
Chimpanzees resolve most disputes with the threat of aggression as opposed to actually engaging in a fight. The gestures and postures they use to indicate threat are as follows: tipping the head, making hitting gestures, flapping hands in the air, sitting in a hunched position, sitting in a hunched position with the head tucked in between the shoulders, swaying branches, throwing objects, flailing arms with a stick in hand, walking in a bipedal swagger, running upright, or charging quickly towards another. These may be combined, and vocalizations often accompany the behaviors. The charging display is the most intense sign of threat and individual chimps have their own distinct way of charging (Goodall, 1986).
Play-Fighting
Play may enable developing and fine-tuning of motor skills and social activities that are necessary for survival as an adult. Play usually incorporates several elements of adult behavior. Some studies have shown that adult behavior can develop normally despite the absence of playfighting, however. Rough-and-tumble play is the most major form of social play in chimpanzees and many other species. Other functions of social play are establishing a sort of dominance order among immature individuals. Without any actual risk of injury, the young who engage in playing get a sense of each other’s strengths and weaknesses. This function of social play is especially pertinent to chimpanzees, who, as adults, engage in actual fighting or threat of fighting to maintain or change social rank. Among younger chimpanzees, playfighting seems to establish a dominance similar to adult structures, but without the tensions and by preventing the rise of conflicts which could result in injury. Chimpanzees use rough as well as gentle play to impress their peers and advertise their rank. While agonistic signals such as threats and submission serve to prevent injury, play seems to have the same effect. Unlike agonism, though, play encourages physical contact in this pursuit of injury avoidance (Paquette, 1994).