ANIMAL COMMUNICATION

the transmission of information from one animal to another by means of sound, visible sign or behaviour, taste or odour, electrical impulse, touch, or a combination of these mediums. In general, communication is employed by animals to attract or repel other individuals of particular groups and to establish and maintain distinct forms of social organization that range from relatively simple pair and family bonds to the highly structured troops of some primates and the complex colonies of social insects. The information involved in animal communication can come from many sources; any facet of the environment perceived is considered information. In linguistic communication the primary function of words is to convey information. Similarly, animals (including man) have modes of behaviour that, in the course of evolution, were selected for their value in providing vehicles for conveying information. During the evolutionary process some of these vehicles also retained more direct functions, but many became specialized for a communicative function alone. These communicative acts, known as displays, include various posturings and movements; sounds; particular ways of making contact among individuals; the release of specialized chemicals called pheromones; and even electrical discharges. Displays have been studied as important means for transmitting information in animal communication. There are, of course, other information sources in animals, some of which have also undergone evolutionary specialization toward a communication function. Among them are what may be called badgesi.e., attributes that are merely structural and nonbehavioral in nature: the red breast of the robin, the red underside of the breeding male stickleback fish, and the mane of the male lion. Many other sources of information can be found in the repeated forms of interaction that develop during prolonged relationships between two individuals and in individual expectations about the nature of the roles in which they encounter others, both familiar associates and strangers. The activities of individuals who interact socially provide a constant and usually rich information source, but, in the study of nonhuman communication, the bulk of systematic research thus far has been directed toward displays and badges; it is, therefore, these highly specialized categories that are of the greatest concern here. the transmission of information from one animal to another by means of sound, visible sign or behaviour, taste or odour, electrical impulse, touch, or a combination of these mediums. The existence, nature, and extent of animal communication have long been subjects of speculation by man and have in modern times stimulated much scientific investigation. Most animal communication employs sound, which has several advantages over other mediums. It fades quickly, leaving no trace of the communicator's location, and it can vary in pitch, duration, volume, and repetition, thus permitting the development of special codes. Sound may also be used in many settings, conditions, and situations in which other means are less feasible, such as in dense forests, across great distances, in darkness, or under water. Most communication is vocal, but there are many exceptions. Male gorillas beat their chests, the ground, or any suitable object, while beavers slap the surface of the water with their tails, sending signals through the underwater tunnels leading to their lodges. Hyenas, which hunt in packs of up to 30, have a rich repertory of grunts, snorts, and giggles. Their complex tracking strategy is guided by their sounds, and once the prey is taken, other sounds, including their well-known laugh, calls the rest of the pack to join in the feast. In contrast, a small bird squawking at the sight of a falcon serves to warn other birds that appropriate actions must be taken to avoid imminent danger. Visual communication may be conducted through the use of badges (i.e., special characteristics such as a patch of bright colour or horns), which give some indication of the communicator's identity (e.g., species, sex, and age). A juvenile baboon, for example, can be distinguished by hair colour, which permits it to act in an immature manner forbidden to adults. Information can also be conveyed visually by the assumption of various poses or motions. Males of many species adopt characteristic attitudes to attract females for mating, and females have evolved various ways of indicating readiness for copulation. Some species set aside a display arena or build a structure that is itself intended as a form of communication, such as the elaborate bower built by the bowerbird. Other visible signs include special dung heaps left by rabbits and the scars left on tree trunks by bears. The use of chemical signals, called pheromones, which are produced by the animal's endocrine system, is yet another form of communication. Ants exude an unpleasant aroma designed to convince a predator of their bad taste. Some pheromones are deposited with urine or feces to mark territorial boundaries, as demonstrated by the familiar habit of dogs. Other chemical signs may be produced by a female in heat to signify sexual readiness or laid down as a trail along the ground, signalling the direction of a food source. There are even pheromones that dictate the hierarchy within a group, but these are the least understood. Touch is less prevalent as a mode of communication than sound, sight, or smell. The dance of the honeybee, which is performed in a dark hive, conveys primarily through touch the direction and distance to a food source; this activity also includes an element of taste, because the honeybee usually has some of the nectar on its body. Some male spiders cautiously announce their presence by strumming on a female's web, indicating that they are to be taken as mate and not prey. Eels and a number of other fishes that live in muddy waters use electrical impulses to send messages to one another as well as to ward off enemies. Additional reading Animal communication is the focus of Charles Darwin, The Expression of the Emotions in Man and Animals, 2nd ed. (1890, reissued 1989), the first major attempt to trace the evolution of facial signals; Wesley E. Lanyon and William N. Tavolga (eds.), Animal Sounds and Communication (1960), accompanied by a phonograph record; Martin Lindauer, Communication Among Social Bees (1961), a fascinating account of evolution in and experiments on social bees; Rene Guy Busnel (ed.), Acoustic Behaviour of Animals (1963), a general survey; and Thomas A. Sebeok (ed.), Animal Communication (1968), with good coverage of various aspects of the subject.