Chimpanzees (Pan troglodytes) inhabit the tropical forests of central Africa. They are distributed from about 10 degrees N to 8 degrees S, and from 15 degrees W to 32 degrees E. They are found from Gambia in the west to Uganda in the east, excluding the region bordered by the Congo and Lualaba rivers in central Zaire (Congo) where their sister species, bonobos (Pan paniscus), are found. (Goodall, 1986; Jones, et al., 1996; Napier and Napier, 1985; Nowak, 1999)
There are three recognized subspecies of common chimpanzee. Pan troglodytes verus occurs in the western portions of the range, from Gambia to the Niger river. From the Niger river to Congo, in the central portion of the range, P. troglodytes troglodytes inhabits forested regions. In the far eastern portion of the range, from the northwestern corner of Zaire into western Uganda and Tanzania, P. troglodytes schweinfurthi is found. (Nowak, 1999)
Chimpanzees utilize a great diversity of habitat types. Although they are typically thought of as living in tropical rainforests, they are also found in forest-savanna mosaic environments, as well as in montain forests at elevations up to 2,750 m. Some populations are known to inhabit primarily savanna habitat. (Goodall, 1986; Jones, et al., 1996; Nowak, 1999)
Adult chimpanzees have a head and body length ranging between 635 and 925 mm. When standing erect, they are 1 to 1.7 m tall. In the wild, males weigh between 34 and 70 kg, whereas females are slightly smaller, weighing between 26 and 50 kg. In captivity individuals typically attain greater weights, with the top weight reaching 80 kg for males and 68 kg for females. Although data from individual subspecies are not available, it appears that P. t. schweinfurthi is smaller than P. t. verus, which is smaller than P. t. troglodytes. Some of the differences seen between captive chimps and wild chimps may be due to subspecific differences in size. (Jones, et al., 1996; Napier and Napier, 1985; Nowak, 1999)
The arms are long, such that the spread of the arms is 1.5 times the height of an individual. Legs are shorter than are the arms, which allows these animals to walk on all fours with the anterior portion of the body higher than the posterior. Chimpanzees have very long hands and fingers, with short thumbs. This hand morphology allows chimpanzees to use their hands as “hooks” while climbing, without interference from the thumb. In trees, chimpanzees may move by swinging from their arms, in a form of brachiation. Although useful in locomotion, the shortness of the thumb relative to the fingers prevents precision grip between the index finger and thumb. Instead, fine manipulations require using the middle finger in opposition to the thumb. (Jones, et al., 1996; Napier and Napier, 1985; Nowak, 1999)
The long hands of chimpanzees also function in quadrupedal locomotion. Fingertips are typically curled upward into the palm during locomotion, and the weight is borne along backs of the fingers. Much of the length of the hand thus contributes to the length of the forelimbs while walking. In combination with the short legs, this gives the back a downward slope from neck to rump, and orients the head into a forward facing position. (Napier and Napier, 1985; Nowak, 1999)
Chimpanzees have prominent ears, and a prominent superorbital crest. This gives the brows a somewhat rigid and bony appearance. A sagittal crest may be present on very large individuals, but is not common. There is no nuchal crest. Cranial capacity of these animals ranges from 320 to 480 cc. The face is slightly prognathic. The lips protrude and are very flexible, allowing an individual to accomplish many tasks through labial manipulation. (Goodall, 1986; Jones, et al., 1996; Napier and Napier, 1985; Nowak, 1999)
Dentition is typical of primates. The dental arch is square in shape, and there is a prominent diastema. Canines are large, as are molars. Molars decrease in size toward the back of the mouth, and lack the enamel wrinkling seen in orangutans. (Napier and Napier, 1985; Nowak, 1999)
The face of adults is typically black, or mottled with brown. Hair is black to brown, and there is no underfur present. There may be some white hairs around the face (looking a bit like a white beard in some individuals). Infant chimpanzees have a white tuft of hair on their rumps, which identifies their age quite clearly. This white tail tuft is lost as an individual ages. (Jones, et al., 1996; Napier and Napier, 1985; Nowak, 1999)
Individuals of both sexes are prone to lose the hair on the head as they age, producing a bald patch behind the brow ridge. Graying of hairs in the lumbar region and on the back is common with age, also. (Goodall, 1986; Jones, et al., 1996; Napier and Napier, 1985; Nowak, 1999)
Chimpanzee reproduction is very complex, and many misconceptions arose early in the study of these animals about the nature of their mating system. Both males and females are known to mate with multiple partners, so they can be considered polygynandrous. However, at times a male may control sexual access to a female, preventing other males from mating with her. A male may do this either through force and dominance in a group mating situation, or by taking the female on a consortship away from other males and thereby securing exclusive sexual access to her. Each of these situations will be discussed at length below. (Goodall, 1986; Jones, et al., 1996; Nowak, 1999)
It is important to note that copulation may serve a number of social functions in this species. Females and males mate more often than would be necessary to ensure impregnation. Copulation may help to develop bonds between males and females. It may funtion in establishing and maintaining group unity. (Goodall, 1986)
Females have an estrus cycle which lasts approximately 36 days. During the course of this cycle, as her hormone levels change, a female experiences changes is the size, shape, and color of her genital skin. As circulating estrogens increase during the follicular phase of the cycle, the size of the swelling increases. When the anogenital skin is fully engorged, it is typically bright pink, and can measure from 938 to 1400 cc. The state of maximal tumescence is of variable length in different individuals and at different stages of maturity, but lasts an average of 6.5 days. It is during this time that females are sexually receptive and that the bulk of copulations with mature males occur. (Goodall, 1986)
The anogenital swelling of females is very important in the sexual behavior of these animals. Most copulations involving mature males and females (96.2%) seen at the Gombe Stream National Park in Tanzania were observed with females who were maximally tumescent. Of the few copulations observed when females were not maximally swollen, almost 75% were performed by one of two adult males, indicating that the propensity to copulate with females who are not at their peak swelling may be something of an individual idiosynchracy. (Goodall, 1986)
The role of the anogenital swelling is many-fold. First, it serves as a signal, visible to males from a great distance, that a female is sexually receptive. Since females tend to be relatively solitary, advertizement of their sexual state to potential mates is essential for reproduction to occur. Males are very interested in the condition of the genitals of each female they encounter. Second, the anogenital swelling may aid females in obtaining food resources including meat. Females who are maximally swollen are often able to supplant more dominant animals at a food source, and are more successful at begging food from males than are unswollen females. Finally, because the males find sexual swellings so attractive, having a maximally engorged genital region may help stranger females to interact peacefully with unfamiliar males as they disperse into new areas. (Goodall, 1986)
There are several possible mating scenarios that males and females may encounter. Each of these is based in part on the phase of the female’s cycle. A female may experience one or more of these scenarios during a particular cycle. The types of situations she encounters depend upon a female’s popularity as a sexual partner, how many other females are in estrus at the same time, how popular those females are, and how attractive the female is to the dominant male.
First, during early tumescence, females are mated by infants, juveniles and early adolescents. Infants and juveniles are probably gaining experience through the copulation, they are unlikely to sire offspring. Mature males do not typically copulate with females until they are maximally tumescent, although exceptions to this rule have been observed. (Goodall, 1986)
In the second sexual scenario, a female who has achieved maximal tumescence becomes the nucleus of a multi-male party. Other estrus females may travel in the same sexual party. These parties can include some or all of community males. During this phase of a female’s cycle, mating can be promiscuous. The males are typically not comepetitive in this situation, and different males may mate with the female in rapid succession. (Goodall, 1986)
The third situation a female might encounter occurs during the second half of maximal tumescence. As the timing of ovulation approaches, dominant males may become possessive and prevent subordinates from copulating with the female. This may involve outright conflicts or, because the dominance relationship between males is well established, may be as simple as the dominant male maintaining close proximity to the female, thereby communicating to his subordinates that the female is no longer up for grabs. Inhibition of the copulations of other males may also occur through threats or attacks. Interestingly, these attacks and threats are often directed at the female, should she express sexual interest in another male. Directing aggression toward the female benefits the male in several ways: 1) it prevents potentially costly fights with other large males, 2) it teaches the female not to copulate with anybody else, and 3) it prevents a third male from mating with the female while the possessive male is punishing another sexual rival. If the possesive male is the highest ranking male in a party, he can inhibit copulations between the female and all other males. (Goodall, 1986)
The result of this restriction of mates late in the course of maximal tumescence has the effect of reducing the number of potential sires for any offspring conceived during that estrus cycle. Since sperm remain viable in the fallopian tubes for 48 hours, only males copulating with a female during the last four days of her swelling could fertilize an egg. Even though a female may mate with many males during any particular cycle, not all of these matings have the potential of resulting in impregnation. (Goodall, 1986)
The fourth sexual mating situation is the consortship. During a consortship, the female may be led away from the group by a particular male. When consorting, male/female pairs often move to the periphery of the community range. Pairs can stay together up to 3 months. During consortship, both members of the pair maintain relative vocal silence, helping to avoid the attention of other community members, as well as attention from the males of neighboring communities who might behave with hostility toward the pair. Consortships inherently involve the cooperation of female. (Goodall, 1986; Nowak, 1999)
Whether males engage in any of these sexual scenarios is highly variable among individuals. A male's preference for, or success in, group mating versus consortships may change depending upon the rise and fall of his fortunes in the constant struggle for dominance between community males. Males who are actively moving up the dominance heirarchy may not spend time away from other males frequently, as in doing so, they may sacrifice social status. Such males, who are in their prime, are more likely to be able to monopolize sexual access to a female in a group situation. High ranking males, especially the alpha male, may take females on consortships, but because of the need to maintain their social standing, these consortships tend to be short in duration. (Goodall, 1986)
It may benefit lower-ranking males to initiate consortships when possible, as in consortships there is no mating competition from other males. This may represent the most likely chance the male has to sire offspring. However, it is harder to entice a female to come on a consortship if she is close to ovulation because of competition/possessiveness of other males. A female may benefit from consortships by being able to choose the male with whom she mates. There may also be better access to food and reduced aggression during a consortship as compared to a group mating situation. However, these benefits must be weighed against the potential cost of encountering hostile neighboring chimpanzee groups when spending time in the periphery of the range. (Goodall, 1986)
Most consortships (40%) at Gombe Stream National Park were initiated when a female was maximally swollen. Only 16% of consortships were intiated when the female was at variable tumescence, and even fewer consortships began when females were flabby (12%) or pregnant (12%). (Goodall, 1986)
To initiate a consortship, a male may gaze toward the female he desires to consort with. This is often accompanied by piloerection (fluffed-out hair), branch shaking, arm stretching, and rocking. If the male succeeds in getting the female to follow him away from the group, he will often walk while looking over his shoulder to make sure she’s still tagging along. This sequence of behaviors may be repeated until the female follows him. If the female does not comply with the male’s wishes, he may become hostile, using aggression to force her to follow him. (Goodall, 1986)
During just over half of fertile cycles, females are confined to multi-male groups. About 21% of fertile cycles occur on consortships. The remaining 15% of cycles occur when young females visit males in other communities. In spite of the numbers of fertile cycles which fall under each mating situation, females are disproportionately likely to conceive during consortships. The exact mechanism of this is not understood. (Goodall, 1986)
Male mate choice
Because males become possesive of females only late in the course of maximal tumescence, it appears that they have some ability to discern the fertile period of females. The ability of male chimpanzees to gauge the potential fertility of a given female can unquestionably be inferred from patterns of copulations. The increase in the copulation frequency of dominant or older males as ovulation approaches demonstrates that males do not respond the same to females throughout the duration of maximal tumescence. Copulations increase as fertilization and impregnation become more likely. In addition, females who were presumed to be undergoing nonfertile cycles (such as during pregnancy and early in the postpartum period) are typically not sexually popular with mature males. (Goodall, 1986)
Aside from potential fertility, one characteristic involved in male mate choice is the age of the female. When presented with two receptive females, males typically show a preference for copulating with the older of the two. Personality traits of individual females may also contribute to males favoring them. A female who is relaxed in the presense of males may be prefered over a more skittish female. Novelty can also play a role in attracting males, since they seem to prefer unfamiliar females over those with whom they have longstanding relationships. (Goodall, 1986)
Female mate choice
Females have some ability to choose the males with whom they mate. They may choose to accept or decline a male’s invitation to consortship. This may allow a female to ensure that a particular male who is low in dominance standing, and therefore is less successful in group mating competitions, sires her offspring. The characteristics of males with whom females consort may vary. It seems that the overall “friendliness” of a female’s relationship with a male may play some role in her choice of him as a consortship partner. Whether the male has played with her, groomed her, or engaged in other friendly behaviors with her as she matured or when she is not maximally swollen, may play some role. (Goodall, 1986)
Although consenting to a consortship clearly demonstrates choice on the part of the female, it should not be assumed that by staying in a multi-male mating party as ovulation approaches, a female is relinquishing her mate choice. She may be choosing to mate with particular dominant individuals. Or, she may be enhancing her social status and familiarity to all the community males by remaining in the group. (Goodall, 1986)
That females discriminate between various males in mating situations is clear. Females avoid copulations with their mature sons and their brothers. There is also some evidence that young females avoid copulations with the older males in their communities (who may potentially have sired them). Although matings do occur between siblings, and occasionally between mothers and their mature sons, the frequency of such matings is much less than would be expected by random pairings of adults within the community. (Goodall, 1986)
Initiating a copulation
Copulations are typically initiated by males. The male sits in what is called the “male invite” posture, with his legs flexed and slightly splayed. This displays his erect penis to a potential mate. A male chimpanzee’s penis is bright pink, thin, and tapered to a point. It is very visible against the black hair and pale skin on the male’s lower abdomen and thighs. The value of the erect penis as a signal may be enhanced as the male “flicks” it-- causing the penis to make a rapid “tapping” movement. (Goodall, 1986)
In addition to displaying his penis, a courting male may show piloerection (fluffed-out hair). A male may gaze directly at a female. Such a gaze directed at a male rival is an unambiguous threat, but in a sexual context appears to serve as an invitation. He may place his raised hand on a branch overhead, and he may shake the branch. This is all a low-key invitation to the female to present her hindquarters to the male for copulation. If he fails to attract the notice of the female, he may incorporate one or more of the following behaviors into his display: arms outstretched toward the female, a bipedal swagger, a sitting hunch, side to side rocking, swaying of vegetation, or stamping with the foot or knuckes. (Goodall, 1986)
Copulation usually occurs in a squatting position after the female crouches and presents her rump to the male. Often, there is no contact between the participants in the mating except at their genitals, although sometimes the male may hold the female. (Goodall, 1986)
Ejaculation is usually achieved within 8.8 thrusts. The copulation is ended as the male scoots back or the female darts forward. Males and females have been seen to clean themselves with leaves after copulating. Females not infrequently consume the vaginal plug (congealed semen) after mating. (Goodall, 1986)
There is no clear seasonality in the reproduction of chimpanzees. Females cycle throughout the year, and males copulate with them when they are receptive. Females may have infertile cycles, such as are seen during the period of adolescent sterility, during pregnancy, and early in the postpartum period. Males copulate with females during infertile cycles as well as during fertile cycles. This indicates that there are social functions other than reproduction related to sexual behavior in these animals. (deWaal, 1982; Goodall, 1986; Jones, et al., 1996; Nowak, 1999)
The female reproductive cycle lasts an average of 36 days. As hormone levels change during their cycle, so does the size of the female’s anogenital swelling. There are four main phases to the cycle, including inflation, as the size of the swelling increases, maximal tumescence. when the sexual skin is fully distended, detumescence, when the previously swollen skin looses all turgidity, and flat, when there is no sign of swelling in the anogenital area. Menstruation occurs about nine days after detumescence begins, and lasts for about three days. Ovulation typically occurs on the last day of maximal tumescence. (Goodall, 1986; Jones, et al., 1996; Nowak, 1999)
Females do not reproduce frequently. There is a prolonged period of juvenile dependence during which the offspring relies on the mother for milk, protection, and education. Becuse of the care required by a single offpspring, females cannot produce offspring frequently. The duration of the interbirth interval varies from population to population. Some of the variability may be due to ecological factors (highly productive habitats may allow females to wean their young sooner, or may result in higher rates of infant survival, both of which would affect interbirth intervals). Because different populations may also represent different subspecies, genetic differences in the timing of reproduction may also be involved. (Goodall, 1986)
Average interbirth intervals range between 3 and 6 years. Gestation lasts from 202 to 260 days, with a mean of 230 days. Typically, a single young is born, weighing about 2 kg. Twinning is rare, but may be more common than in humans. The infant is carried ventrally by the mother for about 3 to 6 months, after which infants may either ride on their mother’s ventrum or on her back. As the young chimp grows, it increasingly rides on its mother’s back during travel. Although young chimps sometimes walk on their own, they regularly ride on mom until the time of weaning at 3.5 to 4.5 years. (Goodall, 1986; Jones, et al., 1996; Nowak, 1999)
The age of independece is somewhat difficult to judge in this very social species. Young chimps can survive without their mother after they are weaned. However, orphaned chimps are often “adopted” by an older sibling or another close relative, who provides the young chimp with care similar to that which the mother would provide. Young typically travel all the time with their mother until they reach puberty. At puberty, females may become the focus of sexual parties, and males become very interested in establishing themselves in the dominance hierarchy. The activities of maturing chimps around the age of 10 years lead to the parting of ways between a mother and her son. (Goodall, 1986; Nowak, 1999)
Females and males enter puberty around the age of 7 years. Females experience a period of adolescent sterility of about three years, during which they cycle, but do not ovulate. During this period, females may transfer into a neighboring chimpanzee community. (Goodall, 1986)
As in humans, there is a great deal of variability between different populations and between individuals within populations in the timing of first birth. Female chimpanzees in the wild give birth to their first offspring between the ages of 11 and 23 years. In Tanzania, the average age at which a female first gives birth is between 14.5 and 15 years. Captive chimpanzees reach sexual maturity at younger ages, and have been known to have babies at ages as young a 7.5 years. However, even for well-fed captive animals, the average age at which a female has her first offspring is between 10.5 and 11.15 years. (deWaal, 1982; Goodall, 1986; Jones, et al., 1996; Nowak, 1999)
Like females, males enter puberty around the age of 7 years. Males of any age, including infants, may mate with females, but these copulations are unlikely to result in impregnation of the female. It is not until males attain social maturity that they can effectively compete for access to females who are fertile. In the wild, males are first seen to ejaculate around the age of 9 years. They do not reach adult weight and social maturity until they are about 15 years of age. (Goodall, 1986; Nowak, 1999)
In general, chimpanzees can be classified into age categories that represent developmental stages. Until the age of 5 years, chimpanzees are infants. From 5 to 7 years of age, chimpanzees are called juveniles. From 7 to 10 years of age, females are called adolescents. Similarly aged males, from 7 to 12 years are also called adolescents. Females aged 10 to 13 years are considered subadults, as are males aged 12 to 15 years. Females are considered fully adult around the age of 13 years, whereas males reach maturity later, around 15 years. (Goodall, 1986; Jones, et al., 1996; Nowak, 1999)
As is true for most mammals, females provide the bulk of parental care. They carry their offspring, groom them, nurse them, and provide them with opportunites to learn all of the complex behavioral patterns of the species. Young are completely dependent upon their mother until weaning at 3 to 4 years of age, but continue to travel with her and rely heavily upon her for support until they reach adulthood. Bonds with the mother extend throughout an individual’s life. In spite of having achieved independence, both males and females may maintain social bonds with their mother for the remainder of their lives. Although females sometimes emmigrate into a new community of chimpanzees, thereby severing ties with their mother, females may also stay in their natal community as adults. In this case, they may occasionally travel with their mother. Males often use their mother for emotional support when establishing themselves in the male dominance hierarchy. When things are not going particularly well for them, some males may seek the comfort, stability, and quiet that only their natal family can provide. (Goodall, 1986; Nishida and Hiraiwa-Hasegawa, 1986; Nowak, 1999)
Because multiple young of different ages may be traveling with their mother at any time, bonds between siblings are also strong. These bonds may remain strong during adulthood, and brothers are frequent allies in intragroup intrigues. Older siblings frequently help to carry infants and play with infants. If the mother should die, older siblings will often assume the care of their immature, weaned siblings. (Goodall, 1986)
Males do not provide any direct parental care for young, although they can be quite gentle and playful with young members of their community, especially those still possessing a white tail tuft. Males may indirectly provide protection for their young. Adult males in the community engage in border patrols, which may help to protect the young from potentially dangerous stanger males. (Goodall, 1986)
The relationship between a mother and her offspring can have many repercussions during the life of the offspring. Although rank is not technically inherited from the mother, the rank of a female does affect her offspring. A mother who has a high rank, who is confident and relaxed in dealing with other chimpanzees, is likely to have offspring who behave in a similar fashion. Nervous mothers may produce offspring who are fearful of other chimpanzees, and who may not do well in dominance competition. (Goodall, 1986)
Because young males do not emmigrate at maturity, they inherit the home range of dominant males. There is no certainty of paternity in this polygynandrous species, so transmission is not directly from father to son and it is unlikely that such relatives would recognize one another as such. Females may remain in their natal community also, although they may transfer to a different chimpanzee social unit upon reaching maturity. (Goodall, 1986; Nishida and Hiraiwa-Hasegawa, 1986; Nowak, 1999)
A variety of ailments trouble chimpanzees in natural habitats, and affect survivorship and longevity. Respiratory diseases, such as colds and coughs, seem prevalent during the rainy season. Gastrointestinal problems, such as diarrhea, peritonitis, and enteritis have been seen and can be lethal, especially in young or very old chimps. Skin ulcers and osteoarthritis have affected some chimpanzees. One chimpanzee at Gombe had a goiter. Abcesses of various sorts have been seen, as have rashes, fungal diseases, and parasitic infections. Even human diseases may sometimes affect wild chimpanzees. A polio epidemic in local human populatons devastated the chimpanzees at Gombe Stream National Park in 1966, killing some and leaving many chimpanzees partially paralyzed.
In addition to disease, injuries are an important source of infections and can lead to mortality in chimpanzees. Injuries may be sustained during falls, or as a result of aggressive interactions within groups or among neighboring groups. (Goodall, 1986)
Because chimpanzees are so closely related to humans, and because they show such intelligence, they have been the focus of many behavioral investigations, both in captivity and in the wild. Over the years, a tremendous wealth of information on the behaviors and social relationships of these animals has been collected. What follows is intended to give the reader an overview of chimpanzee behavior. Necessarily, this account is not exhaustive, nor are all aspects of chimpanzee behavior discussed. Also, please note that discussions of behavior related to reproduction and feeding are found in other sections of this species account.
Chimpanzees are social, diurnal animals. They travel from place to place mainly on the ground, using a form of quadrupedal walking in which the weight is borne on the kuckles. Although they travel on the ground, chimpanzees spend considerable amounts of time in the trees. They feed on fruits while sitting in trees, and arboreal sites are always chosen for resting in night and day nests. Nests are constructed from plant material in trees, and may contain branches from several small trees. Although mothers share their nests with their unweaned offspring, all other juveniles and adults make separate nests in which to sleep. Nests are constructed nightly, and may contain both a bottom platform or mattress, as well as a cover. (Furth and Hohman, 1994; Goodall, 1986; Nowak, 1999)
Chimpanzees are not strictly territorial. Instead, groups occupy a home range, which males and females use differently. Males typically travel farther during a given day than do females (males travel and average of 4.9 km/day versus 3.0 km/day for females). They also range more widely, often visiting the boundaries of the home range. Females, on the other hand, have a core area within the home range in which they spend most of their anestrous time. Females in estrus, though, may range as far as males, as they are likely at this time to travel in mixed sex parties. The exact distance traveled by chimps in a day, a week, or a year, may vary based on food availability, hostile neighboring group proximity, groups size, etc. (Goodall, 1986; Jones, et al., 1996)
Chimpanzees are highly social, and are able to discriminate easily between other individuals. Their memories are long, and chimpanzees who have been taught sign language not only remember individuals they have not seen in years, but also remember the name sign for these individuals. It is likely that such long social memories play an important role in chimpanzee society in natural settings. (Goodall, 1986)
Under natural conditions, chimpanzees live in what behaviorists call a fusion-fission society. The entire community splits into small parties, which frequently travel alone. These subgroups come together from time to time. The composition of subgroups is flexible, so that individuals may travel together sometimes, and at others times travel separately. All members of a community of chimpanzees rarely, if ever, are found in the same place at the same time. (Goodall, 1986; Jones, et al., 1996; Nishida and Hiraiwa-Hasegawa, 1986; Nowak, 1999)
Males tend to be more social than females under natural conditions. At Gombe, males tend to travel in larger parties than do females. Male parties are often centered around sexually attractive females. When females are not in estrus, they often travel alone or with their dependent offspring. Sometimes, two mothers will travel together, giving their young an opportunity to play with one another. (Goodall, 1986)
How much time a particular female spends in large groups versus alone or with dependent offspring is the result of many variables, including how likely the female is to engage in group mating situations versus consortships, how sexually popular she is when she is cycling, and how successful she is at rearing young (which affects the interbirth interval and how often she will have estrus cycles). (Goodall, 1986)
Data from captive chimpanzees indicate that females are not necessarily less social than males. In captivity, females form close bonds with one another, and often have amicable realtionships. The more solitary behavior of female chimpanzees in the wild, then, must be imposed by other factors involved in wild living. It may be that, given the strains of rearing young, the energetic demands of nursing, and the costs of being in a larger group, make solitary life preferable to females. Typically, the smaller group size maintained by females allows them greater access to food. There are also lower levels of aggression in family parties than in mixed sex parties, resulting in reduced risk of injury. (Baker and Smuts, 1994; deWaal, 1982; Goodall, 1986)
Patterns of sociability change during the lifetime of an individual. How social a male is under the age of 8 years depends directly on how social his mother is. As a male matures, he begins to spend less time with his mother, and more time with non-family members. Associations are especially common with adult males and with estrus females. In late adolescence, males may become peripheral, and may spend a great deal of time alone. Around this time, males begin to systematically challenge adult males in the community. The outcome of these challenges affects the dominance status of the male. At all times as adults, males operate within the dominance heirarchy, which impacts all aspects of their behavior. Fully mature males spend little time alone, often being in the company of male friends and rivals, or estrus females. Old males may become increasingly solitary as they near death. (Goodall, 1986)
As is true for young males, the sociability of a young female is related to the sociability of her mother. Unlike her male counterparts, a female does not experience an increased desire for sociality as a young adolescent. However, as she begins to have sexual cycles, a female will undergo some intense social experiences in which she is integrated into the adult reproductive community. As these sexual cycles are underway, a female enlarges her circle of acquaintance, and may spend time, at least temporarily, associating with the males of neighboring communities. Females may transfer to a new community at this time. After the birth of their first offspring, females associate mainly with their families, except when they are cycling. (Goodall, 1986; Jones, et al., 1996; Nowak, 1999)
Relationships within a community
Understanding the social relationships within a community is essential to understanding the dynamics of chimpanzee society. The relationships between individuals change over time as these dynamic animals form coalitions, close friendships, and enemies. Maturation of siblings, death of close associates, changes in the dominance hierarchy of males, and immigration of new females into the community all influence the complex network of social relationships. Goodall (1986) classifies social relationships as friendly, sexual, neutral, or unfriendly. (Goodall, 1986; Nishida and Hiraiwa-Hasegawa, 1986)
There are several sorts of friendly relationships seen in these animals. The relationship between a mother and her offspring involves a high level of protection and assistance. Should a mother die while her offspring is still young, an older sibling or frequent associate of the mother (presumably mother’s sibling) may assume the role of caretaker of the younger chimp. Friends are animals which have stong and enduring reciprocal affiliative interactions. These individuals may support one another against third parties during conflicts. Friendships are common between mothers and their adult offspring, between adult siblings (especially males), and between unrelated adult males. (Goodall, 1986; Nishida and Hiraiwa-Hasegawa, 1986)
Sexual relationships between males and females may be friendly or tense, depending upon the general relationship between a particular male and female. Females may be relaxed and playful with some males, but nervous and tense with others. Sexual relationships may be confined to the time around estrus when males court and consort with females, or they may be more protracted and overlap with friendships. Certainly, a female is likely to be more cooperative in establishing a consortship with a male whom she shares a friendly relationship with than with a male who is aggressive toward her or makes her uncomfortable. (Goodall, 1986)
Most adult females within a community have neutral relationships with one another. The interaction between participants in such relationships is not sufficient to call them either friendly or unfriendly. Such relationships involve females who are rarely together, and who seem to ignore one another when they are. (Goodall, 1986)
Unfriendly relationships are those in which avoidance and aggression are more common to the interactions of the participants than are friendly behaviors. These unfriendly relationships may be competitive, as is seen between pairs of adult males stuggling to best one another in dominance competitions. They also exist with strangers. Females are very hostile to strange females immigrating into their community, although males are usually sexually attracted to such strangers. Males are hostile toward male members of neighboring communities, and may be hostile toward anestrous females from neighboring communities. Males aggressively protect their community boundaries against neighboring males. (Goodall, 1986; Nishida and Hiraiwa-Hasegawa, 1986; Nowak, 1999)
The strongest relationships within a chimpanzee community appear to be between adult males. Adult males spend a great deal of time together. They have been reported as 4 times more likely to groom one another than are females, and from 9 to 20 times more likely to exchange greetings by pant-grunting or kissing than are females. At Mahale, over 80% of the greetings that involved embracing were betweeen males. Relationships between males are highly dependent upon the dominance hierarchy. The hierarchy is mostly linear, with one top-ranking, or alpha, male. This male does not pant-grunt to other males. His status as alpha male is marked by his physical appearance (hair erect, shoulders hunched while walking), and allows him many advantages. Alpha males may take meat from subordinates, displace subordinates at food sites, and may be able to monopolize sexual access to females, thereby achieving disproportionate mating success. (Goodall, 1986; Nishida and Hiraiwa-Hasegawa, 1986)
Because of the advantages of dominance, males compete fiercely for it. Age is a good overall predictor of a male’s position in the dominance heirarchy. Adolescents are subordinate to all adult males. In young adulthood, males are actively challenging older males and moving up the dominance heirarchy. They reach their peak sometime between the ages of 20 and 25 years. Rank declines as a male passes his physical prime, although some individuals may maintain a hold on power until they are fairly old. This may be accomplished through coalitions with other males. (Goodall, 1986; Jones, et al., 1996; Nishida and Hiraiwa-Hasegawa, 1986)
Coalitions between males may affect dominance interactions, and chimpanzees are effective at social manipulations. Both in wild populations and captive groups, relationships and coalitions between males may allow males who could not dominate a third individual by themselves to do so. Males therefore are careful in choosing allies, and spend a great deal of time courting the affinities of particular partners. Low-ranking males may shift coalition partners in ways that are advantageous to them, keeping the hierarchy at higher levels unstable. Instability between the alpha and beta males in a community may provide advantages to lower ranking males by focussing the attention of those two high ranking individuals on their competition with one another, rather than on the “little guys.” In general, brothers are commonly allied in wild populations, but unrelated males are also known to form coalitions. (deWaal, 1982; Goodall, 1986; Nishida and Hiraiwa-Hasegawa, 1986)
An important activity in chimpanzee societies is social grooming. Grooming has many different functions. In addition to helping remove ticks, dirt, and flakes of dead skin from the hair, social grooming helps to establish and maintain social bonds. It provides chimps with an opportuntity for extended, relaxing, friendly social contact. It is often performed in contexts in which it alleviates tension. (deWaal, 1982; Goodall, 1986; Muroyama and Sugiyama, 1994)
During grooming, one individual uses fingers and lips to part the hair of another individual. The groomer searches through the hair of the groomee, looking for any bits of matter which ought to be removed. The act of grooming is frequently accompanied by lip smacking, tooth clacking, and lip buzzing. These noises often increase in intensity when the grooming individual finds something of interest hidden among the hairs of the groomee. During grooming, it is not uncommon for partners in some populations to clasp raised hands above the level of the head. At Gombe, arms of grooming partners are similarly engaged in holding on to branches above the head. The significance of such cultural traditions is unknown. (Goodall, 1986; Muroyama and Sugiyama, 1994)
Patterns of grooming reveal a great deal about relationships between members of a community. An individual is more likely to select as a grooming partner another individual with whom a friendly relationship already exists. Preferred grooming partners are also individuals with whom a better relationship might be socially advantageous. Bouts of social grooming last longest when the grooming is reciprocated. Whether or not an individual responds in kind to grooming is governed by similar considerations. For example, younger males tend to groom older or more dominant males more often than they are groomed by them. Older males are more likely to groom important allies when challenges from young males arise. (Goodall, 1986; Nishida and Hiraiwa-Hasegawa, 1986)
Adult males tend to groom one another with the greatest frequency and for the longest periods of time. Since adult males within a community cooperate to patrol territorial boundaries, good relationships between males may be essential for maintaining the community against neighboring rivals. Grooming between males is likely to be reciprocal. (Goodall, 1986; Muroyama and Sugiyama, 1994; Nishida and Hiraiwa-Hasegawa, 1986)
Males often groom females, but are more inclined to do so when the female in question is in estrus. Often grooming is part of courtship, such that females are more likely to consort with males who groom them. A female’s cooperation in consortship may be important to a male’s chances to mate with her. As such, it benefits a male to maintain friendly relations with a female through grooming. Females often groom with older males, who are likey to be their sexual partners during the fertile portion of the cycle. However, unlike males, females do not use grooming to help establish the sexual relationship. Their attractiveness to males is already assured by the swelling of the anogenital region. (Goodall, 1986; Muroyama and Sugiyama, 1994)
Females groom most often with the members of their immediate family. Adult male offsping may help to support their mother in conflicts within the community, and adult daughters are often a source of companionship. In wild communities, females are hesitant to reciprocate grooming with other females who are not kin. This may result from low levels of familiarity, as captive females, who spend a great deal of time with one another, are more likely to have close female friends and to engage in reciprocal grooming with them. (Baker and Smuts, 1994; Goodall, 1986; Muroyama and Sugiyama, 1994)
Other forms of contact are also important in chimpanzee behavior. From the mother’s embrace, which provides comfort and security to an infant, to touches and embraces during times of excitement, physical contact in non-aggressive situations with other members of the community is common. Such contact provides comfort and reassurance in times of stress. Reassurance behaviors are often directed from a dominant animal to a subordinate after the former has attacked the latter. (deWaal, 1982; Goodall, 1986)
Play is important to chimpanzees of all ages. Although it most commonly involves youngsters, adults may often play as well. Play may be important to the development of social bonds and friendly relationships between individuals, and these relationships may last for life. For example, males and females who play frequently together as youngsters may maintain a friendly relationship leading to consortships as adults. Social play in chimpanzees contains many of the same elements as social play in young humans. Tickling, chasing, and wrestling are common and may be accompanied by laughter. As with other behaviors, the amount of play shown by individuals varies, with some being more playful than others. (Goodall, 1986)
Chimpanzees exhibit complex patterns of behavior, many of which are learned. Chimpanzees acquire information as a result of experience, and that experience modifies subsequent behavior. An individual chimpanzee’s knowledge may be acquired through perceptions (locations of food sources, types of food that are good to eat, etc.), observation (seeing another individual try something and imitating it), trial and error (practicing), or some combination of these. (Goodall, 1986; Tomasello, 1994)
The higher cognitive function of chimpanzees has been demonstrated repeatedly in captivity. Chimpanzees are able to solve problems. They have the ability to abstract and generalize, and they perform cross-modal transfer of information (e.g. object previously felt but not seen can be identifited from photos). In addition, chimpanzees show evidence of being able to plan ahead for anticipated events as well as evidence of remembering past events. (deWaal, 1994; Goodall, 1986)
Tool use and culture
Since the 1960s, researchers have known that chimpanzees make and use tools. Although compared to the computer on which you are reading this account, the tools are terribly simple, their production nonetheless shows foresight, planning, and skill. Chimpanzees often use twigs, sticks, or stems that they have modified as tools with which to fish for insects. Ants and termites are commonly acquired this way. Leaves are used as napkins, and may be crushed in the mouth and used as a sponge to dip for water. Rocks or sticks are used in some populations as hammers to open hard-shelled nuts. In addition, sticks and branches may be used as clubs or projectiles, though for these uses, the raw materials need little or no modification. The tools used, and the uses to which they are put, vary between communities, indicating that there is a pattern of cultural transmission of information on materials and means of production. Female transfer from one community to another may facilitate the spread of novel innovations to naive chimpanzee communities. (Goodall, 1986; McGrew, 1994; Tomasello, 1994)
Within a community, aggressive behavior does not often lead to attacks or physical contact. Males often use displays as a means on intimidation, so that actual attacks are not necessary to maintain social order. However, sometimes physcial fighting takes place, and it can be brutal, resulting in lethal injury. (Goodall, 1986; Nishida and Hiraiwa-Hasegawa, 1986)
Between communities, aggression seems to be the rule. At both Gombe and Mahale, larger communities of chimpanzees exterminated smaller neighboring communities. This was accomplished through brutal attacks between males from the different communities. The duration and nature of attacks on neighboring males clearly indicated that the intent was to do harm. Some males are known to have died from wounds received in this context. The deaths of others have been inferred. (Goodall, 1986; Nishida and Hiraiwa-Hasegawa, 1986)
Chimpanzees can be called territorial, although they do not fit into the ritualized non-violent mode of territoriality common to many other species. In addition to the brutal attacks of neighboring animals, chimpanzees monitor the boundaries of their territories frequently. Groups of animals traveling in peripheral areas are tense and nervous compared to their demeanor when in their core area. Generally however, in territorial species, resident animals win conflicts. With chimpanzees, it seems to be the size of parties, not their location, which influences the outcome of intercommunity interactions. Larger parties are typically victorious. Also, chimps have flexible, rather than stable, groupings. There is often considerable overlap between the home ranges of adjacent communities. And finally, unlike other animals which simply chase their rivals from their territories, chimpanzees are particularly savage in their attacks. They not only attact intruders, but they aggressively search out neighboring community members, often entering the range of the neighboring community in order to do so.
It should be noted that incursions into the territories of enemies, with the apparent intent of harming or killing those encountered, is unique to humans (Homo sapiens) and chimps (Pan troglodytes). The behavior shown by chimps in this context resembles that seen in humans between neighboring enemy tribes. (Goodall, 1986; Nowak, 1999)
An interesting aspect of chimpanzee behavior is their apparent use of medicinal plants. Chimpanzees have been recorded using 13 different plant genera from eight families as possible medications for a variety of ailments. The use of plants with secondary compounds having pharmacological effects has been recorded in at least three populations. Many of these plants are also used by people indigenous to the regions in question for the treatment of stomach upsets, headaches, and parasitic infections. Various compounds have been isolated from these plants, and have demostrated anthelmintic, antiamoebic, antitumor, and antibiotic properties. (Huffman and Wrangham, 1994)
Plants with suspected medicinal value are eaten or processed in manners atypical of normal foodstuffs. Bitter piths may be eaten or sucked, and leaves may be swallowed whole. Also, some of the plants suspected of medicial use by the chimpanzees are only consumed by chimps who appear ill, or at times of the year when illness, especially parasitic infections, are common. (Huffman and Wrangham, 1994)
The size of the home range occupied by a chimpanzee community varies greatly. Both habitat quality and the number of chimpanzees in the community affect home range size. In forest and woodland habitats, chimps are reported to have home ranges between 5 and 50 square km, with an average size near 12 square km. In savanna habitats, where food sources are spread out, chimp communities may occupy home ranges from 120 to 560 square km. (Goodall, 1986; Jones, et al., 1996; Nowak, 1999)
Communication in this highly social species is an area of great interest to human researchers. Chimpanzees in captivity have been involved in a number of experiments designed to show how their minds work with regard to signs, signals, and speech. In this account, communication in wild chimpanzees will be discussed first, followed by a discussion of what language studies in captivity have helped us to understand about these animals.
Gestures such as arm raising, slapping the ground, or a direct stare are threatening signals used between individuals. Male courtship signals, like branch shaking or foot stamping, may be directed at particular female with whom he wishes to mate. Some facial expressions and vocalizations may also be directed at particular individuals. Loud arm scratching while looking at another individual may be interpreted as a request for grooming. (deWaal, 1982; Goodall, 1986)
When excited or fearful, chimps may show low closed grins, full closed grins, or open grins. Snears may also be shown in a fearful context. When the distress is less severe, communicative facial expressions include pouts and horizontal pouts. Compressed lips are often used in threatening displays, and play is generally accompanied by a “play face”, in which the chimp has an open smile with top teeth covered. (deWaal, 1982; Goodall, 1986)
Erection of body hair (piloerection) is an important signal communicating excitement. It occurs in most chimps when a strange or frightening stimulus is encountered, during times of aggression, and in other contexts of social excitment. This bristling of the hair is an autonomic response, so it is not under the conscious control of an individual animal. It is a reliable signal of excitement in this species, just as blushing is a reliable signal of embarrassment in humans. (Goodall, 1986)
In times of fear induced by the behavior or presence of a dominant animal, chimpanzees never show piloerection. Instead, they have incredibly sleek hair, making them appear smaller. Also, the alpha male chimpanzee in a community, although not frightened or excited, almost always has bristled hair--making him appear even larger than he is. (Goodall, 1986)
The swelling of the anogenital skin of females clearly communicates their sexual state to other members of the community. Because the bright pink swelling is highly visible, even at a distance, and can be seen by all, it is considered a non-directed signal. (Goodall, 1986)
All chimpanzee vocalizations are closely tied to their emotions. Their vocalizations are usually spontaneous, signalling the excitment of arriving at a food source, greeting of old friends, or moments of acute fear or distress. However, producing a particular vocalizations without experiencing the underlying emotion seems to be a task that surpasses a chimpanzee's abilities. Conversely, chimps can learn through experience to suppress a particular call in contexts where the vocalizations may lead to an unwelcome result. (Goodall, 1986)
Chimpanzees can be quite vocal. They use a variety of grunts, barks, squeaks, whimpers, and screams. Each call is typically tied to a particular emotional context, such as fear, excitment, bewilderment, or annoyance, so that vocalizations provide information to other chimps about what is happening to other members of their community, even if they cannot see them directly. Subordinate animals direct pant-grunts at more dominant animals. During grooming, chimpanzees often lip-smack or tooth-clack. Play is often accompanied by laughter which, although very raspy-sounding to humans, is similar enough to our own laughter to be easily recognized. Some vocalizations (food grunts) attract other party members to an plentiful food source. Some louder vocalizations (food aaa calls) may attract other chimpanzees in the community from a greater distance. The famous “pant hoot” call of chimps seems to serve as a means of individual identification, and allows friends and family to locate one another even though they may not be within visual range. A detailed listing of calls made by the chimps of Gombe is available in Goodall (1986), and should be consulted by those wishing to know more about specific calls. (Goodall, 1986)
That chimpanzees understand the meaning of their vocalizations is clear from contexts in which they purposefully supress vocalizations. Although typically vocal--especially when traveling in groups-- male chimpanzees are almost entirely silent when they are performing a border patrol, or when raiding into the home range of a neighboring group. It is as if they understand that the success of their mission depends upon remaining covert, and that vocalizations will assuredly attract the notice of neighboring animals whom they would prefer to surprise. Similarly, during the course of a consortship, both male and female remain almost entirely silent. This silence may serve two different functions. First, it may prevent the pair from being discovered by other males in the community, disrupting the temporarily monogamous union. Second, because most consortships take place on the outskirts of the community’s range, silence helps the consorting pair to avoid attracting the attention of neighboring males, who may themselves be out patrolling their borders. (Goodall, 1986)
Various forms of tactile communication occur between pairs of chimps. Physical contact helps to reassure distressed individuals, to placate aggressive individuals, and to appease stress. Embracing, patting, kissing, mounting, and touching all occur in a variety of contexts, including greetings, reconciliations, and reunions. As mentioned in the section on behavior, relaxed physical contact is provided by frequent bouts of social grooming. Such friendly contact helps to cement social bonds. Playful contact, such as finger wrestling or tickling may also occur. (deWaal, 1982; Goodall, 1986)
Although the bulk of physical contact seen in chimpanzees is friendly, there is also physical contact associated with aggression. Hitting, slapping, kicking, and biting also occur, as do pounding, dragging, and stamping. Although such aggressive physical contact usually occurs between two individuals as the result of a specific conflict, it may also sometimes be incidental, as when a chimpanzee is in the wrong place at the wrong time, and becomes incorporated into the display of a dominant or irritated individual. (Goodall, 1986)
Chimpanzees are very interested in smells, and seem to be using them in a variety of contexts. However, the degree to which they use smells, or the specific information they obtain from smells, is not known. Chimpanzees sniff and smell at the anogenital swellings of females. They smell the ground after a mother with a new infant has moved away, apparently trying to catch the scent of the newborn. Individual chimps may have unique odors, recognized by their fellows, but research on this point is lacking. Wild chimpanzees sometimes appear to use scent cues in tracking missing family members. Olfactory cues may be used in helping males to identifiy the approach of ovulation in females, although the specific mechanism or chemicals used for this have not been described. (Goodall, 1986)
Communication Studies in Captivity
Although wild chimpanzees have complex communication, they do not possess what we would call language. They do not use specific calls to identify specific objects or individuals. Indeed, they seem unable to produce vocalizations at will, instead uttering cries and calls as a result of impulsive emotions. However, in spite of having no true language, the mental function of chimpanzees is well developed and they possess many of the cognitive abilities necessary for language to develop, as studies of their acquisition of lexigrams (keyboard symbols) and sign language have shown. (Goodall, 1986; Rumbaugh, et al., 1994)
Chimpanzees can be taught large numbers of signs or symbols, which they can use to respond to questions reliably and repeatably. They can identify sizes, shapes, colors, and can distinguish what attributes of objects make them different (e.g., two circles, one blue, one red, differ in color). They can use abstract concepts and generalize. For example, they can know that a wrench is a tool and a banana is a food. They are able to spontaneously mix and use symbols they know to describe novel objects. For example, one chimpanzee described a cucumber as a “banana which is green”. Further, research has demonstrated that chimpanzees can understand spoken language, responding appropriately to requests, even though they are, themselves, unable to speak. (Goodall, 1986; Rumbaugh, et al., 1994)
Chimpanzees are broadly omnivorous. They rely heavily on ripe fruits and young leaves, with additional consumption of stems, buds, bark, pith, seeds, and resins. This diet is supplemented by a variety of insects, small vertebrates, and eggs. Soil is sometimes consumed, especially that associated with termite mounds, presumably for the minerals it contains. Diets vary seasonally, as different foods are available at different times of year. Diets also vary geographically. Some foods eaten by chimpanzees in one location are not eaten by chimpanzees in another location, even when the food in question is present at both locations, making it possible that geographical differences in diet are cultural. (Goodall, 1986; Jones, et al., 1996; Nowak, 1999; Tomasello, 1994)
Chimpanzees spend the bulk their time feeding or moving from one food source to another. Although foods may be eaten at any time of the day or night, there are typically two major peaks in feeding activities. The first occurs in the morning between 7 and 9 AM. The other is in the afternoon, between 3:30 and 7:30 PM. (Goodall, 1986; Nowak, 1999)
Chimps may use a food source until the food is gone, or they may leave before having consumed all of the food. This may depend upon how many chimps are feeding at the site. Variety in the diet seems to be important, and after consuming enough of a particular food, chimps may move on in search of something else to eat. (Goodall, 1986)
Chimpanzees are known to hunt other large vertebrates on occasion. The largest animals hunted are bush pigs (Potamochoerus larvatus), colobus monkeys (Colobinae) and baboons (Papio). Although adults are sometimes taken, it is more common for chimps to take young animals. (Boesch, 1994; Goodall, 1986; Nowak, 1999)
The predatory behaviors of chimpanzees vary between sexes, individuals, and locations. Males typically consume more meat than females, who seem to specialize more on insect foods than do males. Chimps in the Ivory Coast are known to use more cooperative hunting techniques than the chimpanzees in Tanzania and Uganda. This may be related to differences in the habitat and the behavior of prey. In the Ivory Coast, there is a well developed canopy to the forest, and monkeys may escape chimp predators by climbing high into the trees. In this situation, only cooperative hunting tactics work well for capturing prey. However, at both Gombe and Mahale in Tanzania, the forest is not as dense, and the upper portions of the canopy are not as well developed. As a result, individuals have high success at hunting without enlisting the aid of other chimps. (Boesch, 1994)
Another consequence of habitat differences between western and eastern populations of chimpanzees is that in the east, the colobus monkeys preyed cannot take refuge in areas inacessible to chimpanzees. Under these conditions, colobus monkeys are more aggressive toward the chimpanzees. Coupled with the smaller size of the subspecies of chimp found in this area (P. t. schweinfurthi), a different dynamic is established between predator and prey. Chimpanzees in this area are sometimes fearful of adult male monkeys, and are most likely to attack females with young, in the hope of snatching a baby monkey to eat. (Boesch, 1994)
Cannibalism has been reported in chimpanzees. The circumstances under which this behavior has been observed vary, although typically chimps do not kill and eat members of their own communities. Most commonly, infants killed during intercommunity aggression may be eaten by the males of the neighboring community. However, in a famous case at Gombe, an adult female and her adolescent daughter were responsible for killing several infants of other females in their community. These infants were eaten, often in front of the mother. This behavior ended when the adult female died. The daughter has shown no inclination toward cannibalism since her mother's death. (Goodall, 1986)
Captive chimps commonly exhibit coprophagy and repetitive regurgitation and reingestion. These behaviors appear to be an aberration seen in captivity, as they are not found in wild chimpanzees. (Goodall, 1986)
Finally, sick chimpanzees are known to consume a variety of plants with potentially medicinal value. For a more comprehensive discussion of this behavior, please refer to the behavior section. (Huffman and Wrangham, 1994)
Chimpanzees are hunted as food by humans in many parts of their range. There is no direct evidence of predation on chimps by other animals, although there are some sympatric predators that are likely candidates for taking an occasional chimpanzee--especially young ones. These are leopards (Panthera pardus), pythons (Phython sabae), and martial eagles (Poleamaetus bellicosus). (Goodall, 1986; Jones, et al., 1996)
As predators, chimpanzees may be a factor in structuring populations of their prey species. Certainly, they have a strong impact on red colobus monkeys (Colobus mitis) at Gombe, and they are likely to have effects on other species as well. As frugivores, chimps may help to disperse seeds of certain plants, either through transportation, or by processing the fruit. There are competitive interactions with other primates, and so chimpanzees may have an additional negative effect on other primate species. (Jones, et al., 1996; Nowak, 1999)
Various parsites, such as intestinal helminths, trematodes, and schistosomes, have been reported in these animals. (Jones, et al., 1996)
Chimpanzees, being among our closest living relatives, are of tremendous importance in medical research. They are also heavily used in studies of behavior, both in captivity and in the wild. They are the focus of valuable ecotourism enterprises and are popular in zoos. Finally, there is some illegal pet trade in chimpanzees and they are hunted for bushmeat. (Goodall, 1986; Jones, et al., 1996; Nowak, 1999)
Chimpanzees have been known to prey upon young humans when the opportunity arises, although the propensity for this behavior is closely related to the presence of waste from human beer-making facilities. Chimpanzees eat these attractive, fermented leavings and become intoxicated, making them more likely to become aggressive. When frightened or aggressive chimpanzees can be dangerous, even to adult humans. In addition, because of their biological similarity to humans, they may serve as a reservoir or host for diseases that affect humans. (Goodall, 1986; Nowak, 1999)
Chimpanzee populations are jeopardized by human expansion into rainforests and mixed forest environments. Humans destroy habitats required by chimpanzees for survival and hunt them for bushmeat. They are listed as an Appendix I species by CITES, and are considered endangered by IUCN redlist. The United States Fish and Wildlife Service consideres the species endangered in the wild, and threatened in captivity outside of the natural range.
The scientific name for this species is somewhat misleading. Pan refers to the greek god of forests, and is not entirely inappropriate for these animals. However the term troglodytes means one who crawls into holes or caves. As demonstrated in the report above, these animals do not typically use caves. (Jones, et al., 1996)
Relationships among the subspecies are of interest to many, especially those seeking to understand human diversity by looking at diversity in our closest relatives. Research on the DNA of these subspecies indicates that P. troglodytes troglodytes and P. troglodytes schweinfurthi are most closely related. Their lineages likely separated around 440,000 years before present. In contrast, the lineage of P. t. verus separated from the other common chimpanzees around 1.58 million years before present. Because of this relatively distant relationship, some researchers believe that P. t. verus may warrant elevation to species status. (Nowak, 1999)
Nancy Shefferly (author), Animal Diversity Web, Tanya Dewey (editor), Animal Diversity Web.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
uses sound to communicate
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.
uses smells or other chemicals to communicate
helpers provide assistance in raising young that are not their own
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
A substance that provides both nutrients and energy to a living thing.
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
an animal that mainly eats all kinds of things, including plants and animals
the business of buying and selling animals for people to keep in their homes as pets.
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
scrub forests develop in areas that experience dry seasons.
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
breeding takes place throughout the year
Baker, K., B. Smuts. 1994. Social Relationships of Female Chmpanzees: Diversity Between Captive Social Groups. Pp. 227-242 in R Wrangham, W McGrew, F deWaal, P Heltne, eds. Chimpanzee Cultures. Cambridge, Massachusetts: Harvard University Press in Cooperation with the Chicago Academy of Sciences.
Boesch, C. 1994. Hunting Strategies of Gombe and Tai Chimps. Pp. 77-91 in R Wrangham, W McGrew, F deWaal, P Heltne, eds. Chimpanzee Cultures. Cambridge, Massachusetts: Harvard University Press in Cooperation with the Chicago Academy of Sciences.
Furth, B., G. Hohman. 1994. Comparative Analyses of Nest-Building Behavior in Bonobos and Cimpanzees. Pp. 109-128 in R Wrangham, W McGrew, F deWaal, P Heltne, eds. Chimpanzee Cultures. Cambridge, Massachusetts: Harvard University Press in Cooperation with the Chicago Academy of Sciences.
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