Communication and Perception
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.
Chimpanzees communicate with a wide variety of gestures, postures, and facial expressions. In addition, body language and physical cues are used in communication.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Communication Channels: visual ; tactile ; acoustic ; chemical
Perception Channels: visual ; acoustic