After this display, both groups will usually withdraw to the safety of their own ranges. If the patrolling males encounter a lone stranger or a solitary female with her offspring, the males will chase and even attack. With the exception of a female in heat, researchers have found that male chimps of a community will tolerate no foreign chimpanzees, regardless of sex, within their range.

Aggression between communities is generally much more serious than aggression between the members of the same community. Encounters and conflicts between communities can result in serious injuries or even death, whereas conflicts between members of the same community rarely last even a few minutes.

Each community has a dominant male leader, known as the alpha. The rest of the hierarchy falls into levels of high-ranking males, middle-ranking males and low-ranking males. Powerful alliances and coalitions also exist among both females and males. These coalitions are particularly important when a male needs support to attain or maintain his rank within a community.

In her research, Jane Goodall has determined that a male's rank is not based on physical strength alone. Biologists have observed that some dominance struggles involve such important traits as self-confidence, initiative, resourcefulness and persistence.

There are nearly always some young, low-ranking males waiting for an opportunity to improve their status within a community if they detect an alpha's is in ill health or aging, or if he loses an ally. By repeatedly challenging a higher-ranking male, another male is often able to assume a higher position over an extended period of time.

Young males work their way up the ranks by first challenging the females of the community, and then the senior males. Males usually reach their ultimate spot in the overall hierarchy between age 20 and 26. However, after a male has reached about 30 years of age his status drops, sometimes gradually and sometimes suddenly.

Aggression within a community may occur between males in a struggle for social position or when one family member defends another. Frustration also may cause aggressive behavior. When an individual has been attacked or threatened by an animal of higher rank that he isn't able to challenge within the hierarchy, he may take his frustration out upon some lower-ranking individual in the area.

Females cannot always be ranked in a clear-cut dominance hierarchy. However, several observations have shown that a hierarchy of levels may exist among the females in a community, similar to the levels seen in males. There are often females " who are clearly very high ranking (one of whom often emerges as alpha) and others who rank very low; the remainder fall into a middle-ranking class." A female's rank is greatly influenced by the "nature of her family" and the presence of certain family members when she encounters another female (Goodall-Gombe 437-439).

Males are often said to be "more gregarious" than females and prefer each other's company, except when females are in estrus. Females tend to "spend most of their time with their own offspring - except when cycling, at which time they become very sociable," (Goodall-Gombe 149).

Communication such as posture, touching and grooming, sound, and facial expressions are used to reinforce social hierarchies.

Observations "have highlighted striking similarities in the behavior of chimpanzees and man, notably in nonverbal communication patterns," (Goodall - Shadow 284).

The 'pant-hoot', the most common adult call, consists of a "series of hoo sounds connected by audible intakes of breath, gradually getting louder and usually ending with waa sounds also connected by panting intakes of breath," (Goodall - Shadow 273). The pant hoot is used to maintain contact between the scattered subgroups of a community. Chimps can recognize each other by the sound of individual calls.

Greeting behaviors are used to reaffirm the social status of the individuals involved. The pant-hoot and gestures such as presenting and crouching are important.

A nervous animal may hold out a hand toward the higher-ranking animal, or bow to the ground and crouch submissively with a down-bent head. The dominant animal may then give the lower-ranking animal a reassuring pat or touch, or even hold its hand.

Chimpanzees may also use high- or low-pitched grunts to communicate. "A subordinate chimpanzee is likely to pant-grunt as he approaches a superior during a greeting or after being threatened or attacked. If the superior behaves at all aggressively during the interaction, pant-grunting quickly becomes squeaking or screaming and the chimpanzee grins," (Goodall - Shadow 276).

A frightened or excited chimpanzee may touch or embrace a nearby chimpanzee as a form of reassurance.

Mutual grooming is extremely important in chimpanzee societies.

Aggressive behaviors/gestures may include: hitting, kicking, scratching, hair pulling, biting, stomping, and dragging. After a quarrel, the "vanquished" will often approach his or her attacker, crouch, "weep", and sometimes hold out a hand. The superior animal will then "comfort" the animal it attacked by touching, embracing, or 'grooming' him or her (Goodall/Grzimek 475).

Chimpanzees, like nearly all social animals, may act out disputes with threatening gestures or sounds. This behavior prevents direct combat and possible injury. Males, and occasionally females, may "display" by charging across the ground or through the trees while swinging or dragging branches, throwing stones or sticks, and stomping about. Such displays are important to males in attaining a position of high rank (Goodall/Grzimek 475).

Conflict may occasionally arise between a male and female if the female is "unwilling to follow them in the early phase of courtship". Females are sometimes attacked violently for "reasons not clear to us" (Goodall/Grzimek 475).

Chimpanzees are not always engaged in aggressive behaviors or displays. Chimpanzees also "exhibit a large measure of care, sympathy, and helpfulness towards conspecifics. Usually such behavior pertains to family members, but it will also happen that adults not related to each other will risk their lives for those in danger" (Goodall/Grzimek 481).

Members of a chimpanzee community have been seen embracing, kissing, touching, and holding hands after a period of separation (Goodall/Grzimek 467).

Hear other chimpanzee vocalizations: Food Bark, Bronx Cheer

Breeding and Care of Young

Puberty in both sexes occurs at about 7-8 years of age, but females do not usually give birth until 13-14 years, and males are not fully integrated into the social hierarchy until they are 11 - 15 years old.

Females are capable of reproducing into their 30s and 40s.

The great apes have no 'breeding season'. Males are sexually active at all times. Females have a hormone-controlled cycle usually longer than 30 days. The chimpanzee estrous cycle is approximately 34 - 37 days in length, but there are tremendous individual differences. Cycles ranging in length from 22 - 187 days have been observed.

When a female chimpanzee comes into heat, or estrus, the skin in her genital area becomes swollen. This 'sex skin' is maximally swollen for approximately 10 days. Ovulation occurs near the time of the last day of maximal swelling.

A variety of situations may arise when a female enters estrus. A female may be mounted by most or all of the males in the community, or the highest ranking male may try to prevent others from mating - especially during the last 3 or 4 days of the cycle, when the probability of conception is the highest (Goodall/Grzimek 464).

Chimpanzees are not always promiscuous. A male may form a short-term relationship with a female in estrus and prevent lower-ranking males from mating with her. Male-female pairs may also establish a temporary consortship for up to 3 months. The pair will leave the vicinity of the community and mate only with one another. Consortships are often an effective means for lower-ranking or disabled males to successfully mate.

Gestation lasts 7.5 months, and females usually give birth to one young that will remain with her from 6 to 10 years.

Infants are generally tolerated by all members of the community. Females may carry or comfort infants other than their own. Males are usually tolerant of infants and may pat, touch, groom, play with, comfort, or embrace infants.

During the first few months of their life, young chimpanzees are in almost constant contact with their mothers. Babies less than 5 months of age are "normally protected by their mothers from all contact with other chimpanzees except their own siblings. Infants from the age of 3 months onward often reach out to other chimps sitting nearby, but usually their mothers pull their hands quickly away" (Goodall - Shadow 148).

Social play begins with mother-infant interactions after about 3 months of age. Play may include the mother bouncing the baby on her hands while she lies on her back, mother and infant mouthing each other, play faces, and laughing.

Infants will begin to try solid foods between 4 and 6 months of age.

During the first 6 to 10 months, infant chimps travel almost exclusively in the ventral-ventral position (clinging to their mother's belly).

Chimpanzees at 12-16 months of age "have about as much understanding as a human child of about the same age" (Preuschoft 396).

By 1 year of age, traveling in the ventral-ventral position accounts for about 74% of the travel time (Fulk 26).

Solitary play, which consists of jumping, tumbling, running, and slapping inanimate objects, is very common after one year of age.

Infant chimps may begin to engage in social grooming by infrequently grooming their mother during their first year of life. The frequency of social grooming increases gradually and accounts for about 2 - 3% of a 2 to 3 year old infant's time (Fulk 28).

Youngsters may practice building sleeping nests at an early age. Constant practice helps ensure that a youngster will be skilled at nest making by the time he or she is 4 or 5 years old and ready to sleep on his/her own.

Young chimps also "practice" using twigs and sticks for eating insects.

By age 2, riding on the mother's back is the predominant mode of travel for young chimpanzees. By 3 years, their travel is much more independent.

The time that young chimpanzees spend in contact with their mother decreases over several months. Generally speaking, by 2 years of age, young chimpanzees spend 20 -30% of their time with their mothers (Fulk 26).

Young chimpanzees engage in social play quite frequently. By 3 years of age, the young chimp will be more likely to engage in play with peers. Mother-infant play becomes uncommon after 3 years of age.

Young chimps will often build their own sleeping nests during their final year of suckling. However, they will continue to share a sleeping nest with their mother until a new sibling is born.

Infant chimps are gradually weaned around 4-5 years of age, as their mother resumes cycling.

In the wild, chimps will usually give birth every 5 or 6 years. Also, chimps will continue to associate with their mothers for at least 3 to 4 years after the birth of a sibling. Even 5-year-old captive chimps have been observed to spend 10 - 25% of their time in contact with their mothers.

Family bonds usually last for a lifetime.

During adolescence, females tend to move to a new community and seek acceptance, but males usually stay with the community they were born into.

Subadult males begin to venture out on their own more when they are 8-9 years old. While an adolescent female tends to "plunge into the social life of the community," an adolescent male will tend to become a "more peripheral member" of the community (Goodall - Gombe 168). "A male will associate with other conspecifics and travel around with them. He will maintain 'ties' with his family and finds fresh strength among them in his struggle for rank," (Goodall/Grzimek 465).

After the onset of the first estrus at 9-10 years of age, an adolescent female will begin to venture outside of her family group. A female may transfer to another group permanently or she may form a family of her own in her original home community (Goodall/Grzimek 465).

"After giving birth to her first infant, the female typically becomes less gregarious. As a female gets older, she demonstrates a gradually increasing tendency to spend time with family members only," (Goodall-Gombe 168