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Basic communication modalities in primates (messages which are not under the control of the individual sender) still present information in a coded format, or else it would be very difficult for primates to learn the system. For example, facial colouration patterns in guenons are quite complex. Distinct patterns of red, brown, black, white and blue spots, stripes and eye rings decorate the faces of the12 to 15 gueneon species. These are complemented by crests of hair on the top of the head, the eyebrow region, the 'side burns' area or a beard like growth of hair on the chin. Since these species of small mainly arboreal monkeys are closely related and frequently share the same trees, although eating different diets, and utilizing different levels, they have plenty of opportunity to meet one another. Since sexually mature animals, particularly males, frequently transfer from their group to improve their social rank and mating prospects, it is necessary for them to be able to recognize conspecifics when looking for a new group. Females also must be able to recognize the appropriate species of male if they are in estrus and sexually available. Therefore, the recognition of hair pattern and face colouration is quite important, especially since mixed species troops do exist. Another situation of potential misunderstanding is when a stranger lone animal begins to associate with a troop for its own safety since living alone as a primate is a very risky business.
Within group communication between females and males about sexual readiness is also important and can occur at a basic level. This does not mean that the appropriate response is innate. I have seen a female baboon with a huge estrus swelling presenting repeatedly (standing with her perineum directed at the male's face and looking over her shoulder at him) to a young male who was obviously sexually aroused because he was masturbating his erect penis, but he wasn't even looking at the female. Males must learn what the change in colour and size of a females's perineum means, if the appropriate transfer of information is to occur.
Face colours can also be indicators of sexual receptivity or arousal in both genders. Among Japanese macaques who have rather hairless faces the female's face colour becomes bright red when she is in estrus. Male mandrills who have brightly coloured red and blue faces become positively incandescent when consorting with a breeding female. These markers of sexual readiness and receptivity clearly transmit information not only to intended partner, but to the other members of the group.
It is not only the face which can be affected in the transmission of basic sexual signal. As mentioned above the perineal region (around the anus and vulva) of mature female monkeys often swells and changes colour when she is sexually receptive. This is an important visual cue to primates who may live in large groups or in a forest environment where visibility is somewhat occluded. Chimpanzee males have been observed to spot a flash of bright pink sexual swelling on the other side of a valley and hurry over to investigate. In species such as baboons and some macaques, males form longer term (1 to 3 or 4 days) consort relationships with females and remain in close proximity while grooming and mating. In many cases younger or lower ranking males will consort with females when their swellings are not at maximum size (or when they are young and the swelling is small) but a female with a large estrus swelling is usually the recipient of a lot of sexual interest by males. This is because the swelling usually begins several days before ovulation, and increases until ovulation occurs at which point it begins to reduce. Thus mating with a female at her maximum swelling size will most probably result in conception.
There are additional visual indications of sexual receptivity which change in some primates. These include swelling of the scrotum in males of seasonally breeding species, enlarging of the pink fleshy vesicles on the chests of female geladas and the behaviour of animals who are ready to mate. When discussing behaviour, we move from basic level communicative markers to the interactive level where animals have some control over the messages that they send. In these cases, the decisions to approach or not to approach, to respond or not to respond can be communicative or can reflect the arousal level of the animals. Some individuals simply will not mate with each other and this may indicate close relationship such as brother/sister or mother/son. In some cases one is willing and the other is not. This can lead to conflict in which one animal tries to flee from the other, vocalizes, tries to sit or lie down or refuses to stand in the correct mating posture. This can occur for both males and females, and clearly indicates unwillingness to all conspecific in the vicinity. Some females have been seen trying to pull exhausted males to their feet and get them to mount, especially in a seasonal breeding situation in which all the females are receptive at the same time. Other visual signals include a set of what are called proceptive behaviours by females which are postures and movement to encourage the males to mate. These include presenting the hind quarters, head flagging (shaking the head back and forth) slapping at the male, grooming him and manual stimulation. In addition, some females use particular vocalizations to indicate mating readiness. Males have their own sets of proceptive behaviour as well which vary from species to species. These include genital inspection of females either by sniffing the perineum or touching it with their hands, approaching the females to groom (especially if this is not a common male/female activity as in orangutan), consorting with a female (ie. following her around) touching her hip to indicate that she should stand in a mating posture, and 'bird dogging' which is a posture of Japanese macaque males which looks very much like a well trained hunting dog indicating the presence of a pheasant. In addition are the more overt signals of 'snag crashing' (pushing over trees) dropping branches and loud vocalizations of orangutan males who must attract females from distant locations because they live in fairly solitary lifestyle, and the herding behaviours of chimpanzee males attempting to sequester females during estrus so other males will not find them (termed 'going on safari' in the chimp literature, or 'safari behaviour'). Most monkeys living in groups do not need to use such loud attention getting behaviour, but frequently must be persistent in their signal transmission to get a successful response to their message.
In spite of their impressive nature, displays are not the most common level of visual communicative interaction by most primates. Usually communicative episodes include more low key glances, approaches and shifts in body posture. None the less, these can also be quite complex given the level of differentiation possible in parts of the body and degree of movement. My original work on macaque communication (Taub and King 1986, expanded in Fa and Lindburg 1996) was an effort to describe the movements of the face during threat interactions in Macaca sylvanus, the barbary macaque of Gibraltar. A generalized list of movements of macaque faces had been drawn up before this, but the list was not specific to a particular species and did not consider the possibility of individual variability or variability based on differences due to age of the animal, sex or kin group. Instead, such variability was regarded as noise in a cybernetic system of information transfer. I argued that if there was regularity in this variability then it was not noise, but information added to the message at a metacommunicative level. Briefly stated, my results indicated that Macaca sylvanus used a total of 32 of 34 particular components when making threats. These components were defined as part of the face coupled with a movement, such that eyebrows raise and eyebrows lower were two components. Of these 32 components each individual used between 9 and 20 depending on the individual and the situation. The most interesting discovery was that no components were used in all episodes of sending a threat, which indicates that there is no irreducable core of components that means 'threat'. This discovery has been confirmed by expanding the data base to include Macaca fasicularis (long tail macaques) and Macaca fuscata (Japanese macaques). Only one component in M.fuscata was seen in 100% of the cases. Otherwise, although every individual used the four main components at some time, the patterning of the gesture indicated considerable variability. I divided the components into 3 categories - constant components, variable components and unique components. The idea was to distinguish between those components used by all animals, those used by some and those used only by one animal. However, I found that only one animal used a unique component, so it was not possible to differentiate individuals on the basis of a signature component. When I sorted the components on the basis of use frequency with constant components showing regular use by all member of a species, I discovered that there were only 6 such components in the 3 species examined and only two of these overlapped. In other words, the basic components of threat differ noticeably between barbary, Japanese, and long tail macaques. Not only that, but in barbary macaques all of the constant components were involved with the upper face or piloerection, while both the long tail macaque ones were mouth related components. This indicates that different parts of the face carry different aspects of the message in the two species. When I began to divide the animals in terms of sex and age, I found that some components were used consistently by males which differentiated them from females, and some by females, which differentiated them from males. This occurred in all three species. In Barbary and Japanese macaques the larger proportion of these consistently used components were from the non-mouth region thus reinforcing the pattern of less variable components being non-mouth and more variable components being from the mouth region. This is not, however, the pattern seen in longtail macaques. The same distinction occurred when the animals were divided into old adult, young adult, and subadult categories. The barbary and Japanese macaques showed consistant use of non-mouth discriminators, while long tails discriminated age sets by frequent use of mouth components. The actual components involved are discussed in Chapter 24 in Fa and Lindberg's 1996 'Evolution and Ecology of Macaque Societies." The importance of this level of description and differential is the discovery that the information coding system for threat not only sends ' the threat message' but also operates at a meta-communicative level to send information about the social class (age and sex) of the sender. Even more informative is the fact that in Barbary macaques (which is the only species which I had the data to test for kin group) the three matrilineal kin lines could be distinguished by differential component use, and the one non-kin male distinguished from them. This level of social distinction not only suggests the importance of learning the correct code for your species, but for the social group within the species. The level of information coded included the main message of threat, and the meta level messages of species, age, sex and kin group. This is a very complex coding system and one which was not envisioned when primate communication studies began in detail some forty years ago.
I have only begun to touch on the levels of complexity in coding of visual and vocal signals in primates in this lecture to make it clear that these are not simplistic one or two variable systems, but extremely complex, information rich, multi layered systems of information transmission. Human non-verbal coding may not actually be as complex in terms of layering, but certainly provides a very rich context for our pervasive verbal system.
Fa, J. and Lindburg D. 1996. Evolution and Ecology of Macaque Societies. Cambridge University Press Cambridge.
Jolly, A. 1985. The Evolutionary Primate Behaviour. 2nd ed. Macmillan Publishing Co. London.
Taub, D. And King, F. 1986. Current Perspectives in Primate Social Dynamics. Van Nestrand Reinhold Co. New York.
Zimmerman, E., Newman, J. and Jurgens, U. 1995. Current Topics in Primate Vocal Communication Plenim Press. New York.
King, B.J. 1996. The Information Continuum. SAR Press. New Mexico.