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mise à jour du
29 janvier 2004
communication
71-78
lexique
Yawning serves as a visual signal in primates
Napier JR, Napier PH
The Natural History of the Primates
British Museum, London England
1985

Chat-logomini

Animals living permanently in social groups comprising both sexes and all ages need an efficient system of communication for conveying information about their feelings and intentions to other group members.
napier
Scent signals
 
Nocturnal prosimians, in their dispersed semi-solitary groups, have few, if any, visual signals. At night, a slow loris is just visible to another slow loris by its white nose stripe and contrasting dark eye patches. The face, with its tethered upper lip, is capable of little expression, and the stumpy tail is virtually immobile. In nocturnal primates in general, the closely allied senses of smell and taste are all-important. Pheromones, products of the scent glands, give information about the female's reproductive cycle, probably the most important thing one loris needs to know about another. These are distributed by scentmarking - by rubbing the specialized scent glands on a branch, or by urinating on the hands and feet, thus leaving scented footprints throughout the range.
 
Diurnal prosimians also depend on scent in cornmunication and, in male ring-tailed lemurs, the scent glands are used in a ritualized defence of territory. A specialized scent gland with a sharp horny spur on the inside of the fore-arm is placed against another gland situated above the armpit, thus mingling the secretions. The tail is then drawn clown across the fore-arms so that the horny spur combs deeply into the fur, impregnating it with the odour. The tail is then arched over the back and moved up and clown, wafting the scent towards the opponent in the adjoining territory. At the saine time, the skin surrounding the genitalia is rubbed on a convenient branch. The outcome of this so-called 'stink-fight' is the retreat of one or other of the contestants, and the boundary between the groups is once again established by peaceful means, without actual fighting. Ring-tailed lemurs also establish territory by scent-marking saplings, scraping the horny spur of the fore-arm gland directly against the bark, leaving comma-shaped marks which are impregnated with the scent.
 
In diurnal anthropoids, pheromones also play an important role in communication. In New World monkeys, specialized scent glands on the neck and chest as well as the genital region are used to convey information about age, sex and social rank as well as to mark territory. In Old World monkeys and apes, there are fewer examples of specialized scent glands, and scent signals are probably much less significant than visual signals in social behaviour. The swelling of the female's sexual skin at oestrus in some members of this group acts as a visual signal to males, but this is undoubtedly reinforced by scent signals. Although in field observations the influence of female pheromones can only be inferred, their effect on the mating behaviour of the male has been demonstrated in the laboratory. The sense of smell even influences human social behaviour but, because man is so visually orientated, its importance is not always appreciated.
 
Visual signals
 
In diurnal animals, of course, visual communication is dominant and, with colour vision well developed in the anthropoids, coat colour is vital in species recognition. This is seen particularly in forest-dwelling guenons where striking facial patterns - contrasting spots, tufts, blobs and stripes of colour - accentuate the differences between closely related species living in the same place. This helps an animal to recognize its own kind and thus prevent hybridization.
 
Visual signals include posture, gesture and facial expression; in fact the whole body, particularly the tail, conveys information. A dominant male macaque is instantly recognizable by his confident walk and by the position of his tail which is held upright in an emphatic S-bend; a low-ranking male walks rather furtively with legs bent, his tail carried low.
 
With so many means of expression at their disposal, anthropoids can communicate very fine shades of feeling. A dominant male macaque, for instance, uses a graded series of threat gestures to control his subordinates. First he stares directly at the subordinate; then he opens his mouth (possibly suggesting an intention to bite); then he bobs his head and slaps the ground, while uttering coughing grunts. Finally he lunges at the offender and attacks him. At any stage in the above sequence of events the subordinate can, by making an appeasement gesture, terminate the episode peacefully. The appropriate gesture in many Old World primates consists of the subordinate turning and presenting the hindquarters to the dominant animal who may briefly mount. These ritualized gestures, which reduce tension and prevent fighting, are similar to and possibly derived from the mating postures of male and female.
 
One further visual signal available to mammals is erection of the hair (pilo-erection). This is well displayed in the titi of South America which shows hostility in territorial defence by fluffing up its fur, arching its back and swinging its tail from side to side, all of which makes it look much larger and more aggressive. The remnants of this ability in man were recognized by Shakespeare as a response to extreme fear which, he noted, causes 'each particular hair to stand on end like quills upon the fretful porpentine.'
 
Interpreting the facial expressions of monkeys and apes is not easy. It is not feasible to apply simple concepts such as 'aggression' and 'fear' to the expressions of animals whose feelings can only be surmised. In many cases facial expressions appear to be equivocal. For instance, the retraction of the scalp which reveals the pale eyelids is sometimes used by a dominant animal in threat but also by submissive animals when they are being threatened. The 'lipflip' of the gelada, in which the whole upper lip is everted, is equally difficult to interpret. It is performed by both parties when a male is 'herding' a straying female. Yawning in adult male baboons reveals the long dagger-like canines, and could well be considered a threat, but it may be due to tension in a situation where the animal is uncertain how to react; it may even be a genuine yawn.
 
An invitation to approach is conveyed to another monkey by lip-smacking, the rapid opening and closing of the mouth, sometimes accompanied by rhythmic tongue protrusion. This is seen as a prelude to copulation in marmosets and howlers and in the Sulawesi black 'ape'.
 
The'play face'is common in primates, and consists of a widely open niouth, usually with the upper teeth covered and the lower teeth exposed. The animal soliciting play looks (but does not stare or glare) at another individual and approaches it with exaggerated body movements, sometimes pouncing on it and pretending to bite. Like the yawn, the open mouth can have two meanings, depending on its context: in play it is a relaxed lively expression whereas in aggressive interactions it is tense and threatening.
macaque
Auditory signals
 
These are important in the forest where foliage blocks visual cues. Diurnal forest dwellers have a large repertoire of calls which convey information about age sex and social role just as surely as the olfactory signals of prosimians. As the facial skeleton and larynx develop during growth, so the pitch and resonance of the voice alters. The 'great call' of the adult female gibbon cannot be imitated by a juvenile, neither can the deep roar of adult male howlers which once terrified explorers of the New World who mistook it for the growling of jaguars. The characteristic loud call ('whoop-gobble') of the adult male mangabey, Cercocebiis albigena, is produced for the first time at about six or seven years of age, a phenomenon comparable with the breaking of the voice in human males, and similarly indicating the attainment of sexual maturity. Many male and, female 'monogamous' primates (e.g. gibbons, tarsiers and titis) combine their different calls in a duet which is usually associated with territorial defence. The fluent performance of the duet indicates long practice and thus the presence of a stable mated pair.
 
These are all 'spacing' signals, locating a group in the forest for the information of other groups. Within a group, members keep in touch by means of 'contact' calls: black-capped capuchins in the Colombian rain forest give a low soft whistle which carries a short distance, and a strong high-pitched whistle to contact members who may be as much as 200 metres away.
 
Most arboreal primates give a distinctive warning call in the presence of raptorial birds, enabling the rest of the group to seek shelter in the lower strata of the forest. The partly ground-living and partly treeliving vervet monkey of Kenya has gone one further. It has evolved the ability to give different alarrn calls for several different types of predator - leopard, eagle, snake and baboon. These signals elicit appropriate responses from other group members: for instance the eagle alarm call causes vervets immediately to look upwards and run into cover; the snake alarm call makes them look clown on the ground around them, and the leopard alarm makes them run up a tree or, if they are already in a tree, climb higher. In giving the various calls, adults show very accurate identification, readily distinguishing the dangerous martial eagle from less deadly types of predatory bird. Infants are less able to discriminate and give eagle alarrn calls for a variety of birds from vultures to pigeons - even for a falling leaf.
 
Grooming
 
Finally the sense of touch is used in communication by most primates and takes the form of mutual, or reciprocal, grooming. This activity consists of one partner approaching another and presenting a particular part of its body. The other partner responds by grooming the fur, parting it to examine the underlying skin and picking off flakes of dry skin, dust, dirt or parasites. Each area of skin is carefully and systematically cleaned, and particular attention is paid to the face shoulders and back, and to scratches and wounds. Then roles are exchanged: groomer becomes groomee and another session begins. Judging by the intent expression and persistence of the groomer, the act of grooming is an absorbing task, and from the total relaxation and abandon of the groomee, being groomed is a most soothing experience. What probably originated as a purely hygienic exercise, has become in monkeys and apes a valuable social bond.
 
Grooming the fur is as important in mammals as preening in birds. Prosimians Lise the dental comb and toilet claw for self-grooming. A lemur scratches itself like a dog and washes itself like a cat; furthermore the lemur's dental comb acts as a substitute for the combing action of the cats rough tongue. In mutual grooming, a lemur does not use its hands except to grasp its partner by the head or ears to hold it still while it licks the fur, using the dental comb to free any matted hairs. From time to time the sublingua is used to clear the comb of any accumulated hairs which are swallowed. It is significant that prosimians, the primates with the least dextrous hands, have evolved two supplementary aids - the toothcomb and the toilet claw - to help them in the essential task of keeping the fur clean and comfortable.
 
Some form of grooming is seen in all anthropoids, though there are variations in the amount of time devoted to it. In chimpanzees, grooming sessions last for hours and undoubtedly do more than keep the coat clean, important though this is. Grooming unites mothers and their offspring in regular grooming parties, thus strengthening family ties. It allows young animals to approach adults in a relaxed atmosphere. It communicates feelings of relaxation, amity and well-being, and is a vital link in the cohesion of the group.
 
Another form of tactile communication adopted by the douroucouli and titi of South America is tailtwining. Two or more animals sleep bunched on a branch with their tails entwined, demonstrating the mutual attachment of these family groups.
 
Chimpanzees seem to approach closely to man in their gestures of greeting and reassurance in which the sense of touch is dominant. When chimpanzees meet after a separation, as often happens in their informal type of social organization, they may embrace, hug, kiss, hold hands, touch or pat each other, depending upon the degree of friendship between thein. In moments of sudden alarm, a chimpanzee will reach out to touch another, deriving reassurance from the contact. These gestures are so like those of humans that it is impossible not to accept them as the counterparts of the human gestures they resemble .
Pandiculation: the comparative phenomenon of systematic stretching AF Fraser