Communication, Animal

I. Social and Psychological AnalysisJarvis Bastian

BIBLIOGRAPHY

II. Communication Models and Signaling BehaviorThomas A. Sebeok

BIBLIOGRAPHY

I SOCIAL AND PSYCHOLOGICAL ANALYSIS

It is not easy to mark the boundaries of the subject of animal communication. Some quite good reasons might be offered for viewing the subject as encompassing all phenomena of life, for the very notion of biological adaptation can be said to involve an animal population’s or, more to the point, a gene pool’s communication with its environment. Even when biological adaptation is considered only at the behavioral level, this broad view may seem increasingly appropriate as we come to appreciate heretofore unsuspected ways by which animals communicate with their environments—such as the echo-ranging systems of the dolphins. But however impressive the echo-ranging systems of dolphins, bats, eared seals, and so on, are, they are no more (nor less) marvelous than, say, the olfactory systems of carnivores or the visual system of higher primates. An active wresting of adaptively pertinent information, rather than a mere reacting to environmental changes, is a characteristic feature of all higher modes of adaptation.

Thus, there is usually little advantage to be gained from viewing animal communication as extending across all of an animal population’s interactions with every aspect of its environment, and it is common to restrict most discussions of the subject to what may be called social communication. This is a valuable restriction, for with the exploitation of social modes of adaptation, an additional range of environmental information becomes significant, namely, that arising from the social environment. The problems associated with these adaptations are quite special because the reciprocity of influence and concomitant fluidity in social interactions is usually much greater than in the interactions between animals and their nonsocial environments. This is not to say that the processes and mechanisms of social interaction are necessarily different in kind from those involved in interaction with nonsocial environments but only to point out that pressures related to social factors have been involved in their evolution (Wynne-Edwards 1963). It is because of this that it is especially reasonable to distinguish social communication as a special part of the more general problem of the communication of animals with their environments.

However, in making this distinction we must be careful not to make social communication conceptually more special than it really is. Most often social communication is considered a subordinate part of social behavior. This is clearly wrong, for, basically, social communication and social behavior are identical. At bottom, can anything more be said of social behavior than that it is the partial, and mostly reciprocal, determination of one or more animals’ actions by other animals? And, reversing the coin, can the occurrence and reception of communicative signals be something more than just this social behavior? There are probably many reasons why social communication has been mistakenly thought to be a subject set apart from the rest of social behavior. No doubt some are related to the apparent ease with which we seem to distinguish man’s linguistic actions from the rest of his social interactions. But man’s linguistic activities constitute an exceedingly specialized form of animal communication, and it is well to bear constantly in mind that it is extremely risky to apply generalizations and ideas having their basis in what we feel to be the properties of linguistic communication to nonlinguistic communication. (Caution in proceeding in the reverse direction is at least equally warranted.) Actually, nonlinguistic modes of communication are exploited as much by humans as by any other social fauna, and if we were to attend only to these, the inclination to separate communication from social interaction would surely diminish.

The distinction between social communication and social behavior is also promoted by the feeling, again prompted by a presumed analogy to human linguistic actions, that successful communication involves the transmission of information or some other commodity. That is, it is thought that in communication something is literally made common to both signaler and recipients that would otherwise remain the private possession of the signaler. This notion is also linked with the idea that communication occurs only when one animal, the signaler, performs some sort of action and by this action generates the signal whose reception by others constitutes the information transmission. One of the difficulties with this formulation of animal communication is that there are many situations in which an animal may affect the conduct of others in its group, not through any actions of its skeletal musculature, but simply by sensory attributes of its body over which it in no sense can be said to have control, such as the coloring of its feathers or of its beak. Even when the communicative events derive from particular behavioral acts, the applicability of the notion of information transmission is open to question, although to whatever extent it is applicable it is just as much so to all of social behavior. In animal communication the information that might be said to be transmitted is precisely the social significance of any attribute, behavioral or otherwise, of the participants in any social interaction.

Signaling systems

Nonetheless, specializations in social modes of adaptation do occur very widely, even in species not routinely living in groups, in which specific actions by one participant appear to function primarily to produce patterns of stimulation that characteristically evoke regular changes in the behavior of others. Such conventionalization of the means of integrating animal social behavior can well be regarded as signaling systems, always appreciating that we are only referring to especially systematic, regularized episodes of social interaction. Social specializations of this sort, as with any biological specialization, are the more pronounced the more directly they contribute to the integrity of a species, and thus, animal signaling systems appear most often in the government of social episodes relating to biologically critical areas, such as reproduction and infant care, species and group integration, spacing and population control, predator defense, cooperative foraging, etc.

There are many questions about any animal signaling system that require answers if we are to develop an understanding of these parts of biology. To date none have been more than partially answered for any single species, and as the answers can certainly be expected to be interrelated not only with each other but also with the immense numbers of other questions remaining to be answered about any species’ mode of adaptation, we can view our current state of knowledge only with despair. But however woefully lacking in answers, we will discuss these questions in three very much overlapping groups, relating in turn to the structures, functions, and mechanisms of animal signaling systems.

Structural aspects . The most basic structural question concerns the physical nature of the signals. For any species this depends on the nature of the afferent and efferent adaptations and on the demands of the habitat. In principle every available avenue of exteroception is potentially exploitable for mediating social intercourse, and in fact, all are exploited by one animal form or another. There are, of course, restrictions imposed by sensitivities of the receptor systems and by glandular and motor capabilities for generating signals commensurate with these sensitivities. For instance, exposure of colored surfaces could have no value for intraspecific signaling in color-blind species. But many other factors (carefully reviewed by Marler 1961a) may participate in the selection of signaling modes that are perhaps less apparent—as for instance, the time and distance over which social interactions occur, the sources of signal distortion in the signaling medium, and the exposure to predation associated with signaling actions. Because signaling systems are intrinsically social phenomena, their adaptive exploitation requires the characteristics of signal emission, transmission, and reception to be well matched, to insure the effective mediation of social episodes.

This brings us to questions concerned with the nature of the particular signals, where similar degrees of complexity must be faced. Only detailed, systematic investigation can reveal which features of a given signal possess social significance, i.e., are critical in determining the results of signal reception. Fortunately there have been some very notable successes in developing appropriate methods for identifying the critical stimulus features governing social interactions, such as are described by Tinbergen (1951; 1953a). Ideally, the most effective procedure exposes animals to models incorporating stimulus variations of the features of the naturally occurring signals and measures the effects of such variations on the conduct of recipients. This has been practicable in a number of instances where the natural signal involves only a single sensory mode and remains relatively stable for long durations, such as the chemical signals that have been isolated as parts of the social adaptations of various insects (Wilson 1963). Even with auditory signals, which are usually much briefer and less steady, advances in recording and reproducing techniques have made it possible to employ a close approximation to the model-manipulation approach by selective filtering of recordings of the original signals in order to determine the behavioral effects (Busnel 1963; Falls 1963); and it can be expected that before long the very close parallels to the model-manipulation procedures that have been so productively used in the analysis and synthesis of human speech sounds (e.g., Liberman 1957) will begin to be used with equal effect by animal behaviorists concerned with acoustical signaling.

Unfortunately, the full power of the model-manipulation method can perhaps never be fully brought to bear on the problem of identifying the significant features of many kinds of animal signals. This is because, especially in social episodes involving close proximity of the participants, the signals may involve several sensory modalities simultaneously. The difficulties are further intensified when the features of the signals are produced by many different concurrent motor adjustments, as in the signals of some carnivores and terrestrial primates (Hinde & Rowell 1962; DeVore 1965).

When the signals are shifting patterns of multimodal stimulus combinations, the determination of the contribution made by each aspect to the significance of the total complex may never be complete. Nevertheless, the ingenuity of investigators and the prospects for exploitable technological developments in manipulating complex stimulus events in the field or laboratory, if not limitless, are at least sufficiently unpredictable to permit the hope that much progress can be made in analyzing the constituents of even the most complex and fluid signals, for we know that signal complexity cannot exceed the socially effective resolution capacities of its recipients. We appear to be further aided in meeting this problem of signal complexity by the seeming absence of gestalt properties in their reception (Hess 1962). That is, the social effects of parts of a signal complex may interact in simply an additive fashion, so that the effects of subsets of the total complex may be studied separately. This possibility is well illustrated in studies by Miller and his associates (1959) in which they compared the stimulus values of (1) fearful monkeys, (2) life-size still photographs of fearful monkeys, and (3) life-size still photographs of just the facial regions of fearful monkeys in evoking conditioned avoidance responses in other monkeys. They found that all three different stimulus complexes were effective, which suggests that such conditioning procedures, together with advanced techniques of stimulus manipulation, might very well be valuable in analyzing critical features of even the most complex social signals.

Perhaps an even more imposing barrier to the exploitation of the model-manipulation method is raised by the evidently very important role played by context effects in determining the behavioral consequences of the signals, especially the more elaborate modes of social adaptation. Thus, apparently, the same signal emitted in different social contexts (Schaller 1963) or following different prior signaling actions (Altmann 1962) does not evoke the same behavioral effects. As a result of such difficulties, this extremely valuable technique of analyzing the stimuli that control general animal behavior may be of limited use in studying many kinds of signals operating in social interactions.

But there is no reason for pessimism. Careful field observation by competent (ecologically oriented) workers aided by good cinematic and audio field recording can be expected not only to yield precise identifications of the signals occurring in conventional behavioral interactions but also to disclose what are their more or less invariant features—though perhaps not the particular contribution made by each, nor their interactions, in determining the behavioral effects of signal reception. These prospects are heightened by the relative stability of animal signals. In profound contrast to human linguistic signals, which change incessantly and with great rapidity, nonlinguistic signals of man and other animals tend to be steady and to remain so for long periods of time. And since even the fluctuating auditory displays of songbirds (Thorpe 1961 a) and dolphins (Dreher & Evans 1964) tend to occur as repetitive trains, we can hope to attain rather close specifications of these signals.

Not only must extended observation of free-ranging animals be relied on to furnish much of the information needed for determining the particular physical characteristics; it is also required to provide additional structural data essential to understanding the functioning of any signaling system. We need to know the features of as many of the signals as possible, how variable each is, and to what degree the different classes of signals intergrade. We also need to know their distributions of occurrence in an animal population, in terms of their grading by age, sex, and social status and in terms of the presence and ranges of “dialectical” differences.

Another very important question is whether signals or their constituent features occur in different simultaneous or sequential combinations. That is, do these systems possess syntactical properties? So far only very few combinatorial phenomena have been found that are loosely analogous to the syntactic operations of intensification in human languages. However, the foremost advantage of syntactic systems is the large number of different events provided by a few combinatorial elements, and as far as is known, nonlinguistic signaling systems involve impressively small numbers of different signals.

Functional aspects

Once some degree of resolution can be provided for questions concerning the structural properties of animal signaling systems, combined observation and experimentation in the field and laboratory is also indispensable for answering the next broad set of questions—those addressed to the functioning of the systems. These questions occur on at least two levels. The first is concerned with the functional determinants of the glandular–muscular actions of the participants in a particular social episode; the other is concerned with the functioning of such episodes on an ecological level, that is, in the contribution that these conventionalized behaviors make to the species’ over-all mode of adaptation. Questions on both levels must be posed in terms relevant to the social and ecological settings into which the evolution of these signaling processes has fitted them. Although it is completely clear that deep understanding of functional problems cannot be achieved without recourse to experimental methods, the scientific value of the uses of such methods is directly proportional to their degree of congruence with information concerning the nature of the ecological adaptations of animal populations.

Before pursuing these functional considerations of animal signaling systems any further, we should pause briefly to immunize what is to follow against some of the conceptual poisons that so easily infect discussions of this kind. Fortunately, most of the deleterious aspects of the biologist’s notion of function have been removed by the recognition of the worthlessness of teleological explanations for the teleological mechanisms that so pervade the phenomena of life. But they continue to pose a threat when the functioning of communicative acts is considered, because of the seductive qualities of thinking about signaling actions in terms of the purposes or intentions of the signaler. It is quite easy to avoid such thinking by thoroughly appreciating that animal signaling actions, such as the “waggle” dance performed by workers of some species of bees, are purposive in exactly the same way as a shark’s kidneys or a sparrow’s hemoglobin. Some day, perhaps, a behavioral theory will be developed in which the notion of purposive actions appears in a way that goes beyond the general idea of biological adaptation and that sharply distinguishes, say, only some kinds of human actions as purposive in this special sense. Until then the term “purposive” will be a predicate more of features of biological populations than of specific actions, and we might do better just to use the term “adaptive” and get on with the task of discovering the specific features of particular signaling, neuromuscular, renal, and biochemical systems and how they function to confer selective advantage on their possessors.

On the behavioral level two principal questions about the functioning of signaling systems confront us. The first is concerned with the circumstances of an animal’s environment (external and internal) that determine its signaling actions and can be taken as concerning the reference of the signals generated by such actions. The second question concerns the behavior changes contingent upon signal reception, or what may be called the significance of the signal. Because the reference of a signal may be only indirectly connected to its significance, describing the functions of signaling systems in terms of transferring information or conveying meaning may often be quite strained. Even when the reference and significance of a signaling action can be specified, nothing is added on the behavioral level of analysis by assertions about the information transmitted or the message conveyed, although these may be warranted, and indeed important, considerations on an ecological level of analysis.

The emotional components. In examining the events of signal emission from a viewpoint somewhere between the glandular–muscular and ecological levels of analysis, one gets, along with Darwin and many others, a strong impression of their fundamentally emotional character. That is, signal emission is associated with shifts in the levels of arousal of emotional or drive states in the animal, induced by the environmental changes to which the signal refers. This characterization is, of course, flagrantly anthropomorphic and becomes increasingly objectionable as the signaling systems of animal forms below the birds and mammals are considered. At present there is not much meaning to discussions of the emotional qualities of a spider’s courtship behaviors. Nevertheless, to the degree that the term “emotional” can be provided any technical meaning with respect to human behavior, this anthropomorphistic usage does have some measure of justification, because of the emotional character of much of man’s nonlinguistic signals, particularly those emitted by human infants, and their apparent homology with the signals of other animal forms (Andrew 1963; Schaller 1963). Actually, a more forceful objection to the emphasis on the emotional qualities involved in the processes of animal signal emission might be that they are quite unexceptional in this regard. If the bulk of all animal behavior, man’s included, were organized and activated by emotional processes, then accounting for the apparent exceptions would present the most challenging problems. Perhaps the most notable of such exceptions would be those forms of human interaction, mediated by linguistic signaling systems, that appear to be specifically protected, though often only flimsily, against emotional influences by traditional conventions (Hebb & Thompson 1954). But even when linguistic signals do not refer to emotional processes (though they very often do), much of the variation in their linguistically nonsignificant features is subject to emotional determination.

Not only do animal signaling actions appear to be associated with emotional processes in the emitter; their significance, that is, their effect on their receivers, is largely emotional as well. Characteristically, the consequences of signal reception involve changes in the emotional status of the receiver, frequently leading to its emission of signaling actions in turn, which evoke further emotional changes in the initial signaler, and so on, until sometimes quite elaborate interaction episodes, such as the courtship patterns of many birds, are sequentially unfolded in this way. Obviously, there is more that transpires in such episodes than just exchanges of signals, but the important point is that the actions of the participants are steered by the emotional changes arising from signal reception.

Mechanisms

The strength of these restrictions is unknown, but it has an important bearing on the kinds of answers that might be proposed to questions about the mechanisms governing signal emission, the behavior consequences of signal reception, and the development of these mechanisms in species and their members. The specific features of these mechanisms have not been established for any species, but gratifying progress has been made in determining the general nature of neurochemical components of the mechanisms and their dynamics, particularly for some avian species (as, for instance, in the work of Lehrman 1962; Schein & Hale 1959; Hoist & Saint Paul 1962).

This work suggests that whatever the various mechanisms may be, we should be prepared to expect them to be no different from the mechanisms governing other, nonsocial behavior. Similarly, we can expect the development of their components to involve interactions of various sorts between genetic and experiential factors (Marler 1963). And we should not be surprised to find, especially for the more advanced forms, that different developmental histories underlie the mechanisms governing the emission of different signals or the responses to them in a given species. For instance, it could very well be that for a particular signal hereditary factors are more penetrant in the development of the mechanisms governing its emission than the behavioral results of its reception, or vice versa. Because of this we may find that certain signaling mechanisms in some animals are highly plastic, not only in terms of their references, but also in the physical form of the signals they produce. This is already well established for phonatory signaling of certain species of “talking” birds (Ginsburg I960; Grosslight et al. 1962), but more surprisingly, the techniques of operant conditioning have also been used to manipulate vocalization of some nonhuman mammals, such as the domestic dog (Salzinger & Waller 1962), the house cat (Molliver 1963), the bottlenose dolphin (Turner 1964), and the chimpanzee (Hayes & Hayes 1950).

However, it is far from clear that any of the above cases represents a departure from the emotional character of these signaling actions. The degree to which the activation of these signaling mechanisms may be divorced from emotional processes is a particularly exciting question, for the answers may yield a better understanding of the basis of this independence in human speech (Geschwind 1964).

Jarvis Bastian

[Other relevant material may be found inEmotion; Ethology; Imprinting; Instinct; Kinesics.]

BIBLIOGRAPHY

The bibliography for this article is combined with the bibliography of the article that follows.

II COMMUNICATION MODELS AND SIGNALING BEHAVIOR

To understand the ways whereby animals communicate with each other requires the cooperative attack of a wide variety of disciplines, ranging from bioacoustics and biochemistry through anatomy to sensory physiology and neurophysiology, and from comparative psychology and zoology to anthropology and linguistics. The diverse lines of research that have converged on the study of animal communication—which, in turn, seems so far to have constituted the principal axis of synthesis in the entire field of animal behavior—may together be subsumed under the label zoosemiotics. This word was coined (Sebeok 1963a, p. 465) to emphasize the necessary dependency of this emerging field on a science that involves, broadly, the coding of information in cybernetic control processes and the consequences that are imposed by this categorization where living animals function as input–output linking devices in a biological version of the traditional information-theory circuit, with a trans-coder added. Thus, the science of zoosemiotics lies at the intersection of general semiotics, the doctrine of signs, and ethology, the biological study of behavior [seeEthology; Semantics and semiotics].

zoosemiotics

The essential unity of a zoosemiotic event may be decomposed, for a field observer’s or laboratory experimenter’s convenience, into six aspects, and the sphere of animal communication studies has in practice tended to divide roughly in accordance with these dimensions. The hexagonal model which is suggested here (Broadhurst 1963, chapters 2, 3) entails a communication unit in which a relatively small amount of energy or matter in one animal, the source, brings about a relatively large redistribution of energy or matter in another animal, the destination, and postulates a channel through which the participants are capable of establishing and sustaining contact. Every source requires a transmitter, which serves, by a process called encoding, to reorganize the messages it produces into a form that the channel can accommodate; and a receiver is required to reconvert, by a process called decoding, the incoming messages into a form that can be understood by the destination. The source and the destination are therefore said to share, at least partially, a code, which may be defined as that set of transformation rules whereby messages can be converted from one representation to another. An ordered selection from a conventional set of signs is a message. The physical embodiment of a message is a signal, which is usually mixed with noise. (The term “noise” here refers to variability at the destination not predictable from variability introduced at the source.) Finally, to be operative, the message presupposes a context referred to and apprehensible by the destination.

The origin, propagation, and effect of signs can be studied by an examination of the manner in which an animal encodes a message, how this is transmitted in a channel, and how the user decodes it. Since any form of physical energy can be exploited for purposes of communication, a primary task is to specify the sensor or constellation of sensors employed among the members of a given species or among members of different species. Organisms may have sensors for chemicals in solution or dispersed in air (taste and smell), sensors for light (vision), sensors for pressure changes (tactile perception or hearing), or still other sensors involving, for example, parts of the electromagnetic spectrum besides the visual portion. Many animals employ multiple sense organs: thus, communication among bees involves olfactory, optical, acoustic, and other mechanical signals; a herd of mule deer achieves social integration by hearing, vision, smell, and touch.

Chemical systems provide the dominant means of communication in most animal species (Wynne-Edwards 1962, chapter 6; Wilson & Bossert 1963; Bossert & Wilson 1963) and perhaps even in birds. Information is transferred by substances referred to as pheromones (Wilson 1963). Chemical signals may be emitted by an animal’s entire body cover, the skin, by special scent glands (e.g., as in ruminants), and by still other parts of the body. They may be received throughout the body (e.g., as in some aquatic invertebrates) or by specialized structures called chemoreceptors, that is, by the distal organs of smell and the proximal organs of taste. It is as yet unknown whether any animal can modulate the intensity or pulse frequency of pheromone emission to formulate new messages. Pheromones tend to function as yes–no signals: a particular scent either is produced or it is not; once emitted, however, the odor is very likely to persist and, thus, convey a message after the departure of its source from the site. The one great advantage, therefore, of chemical signals is their capacity— exploited for social integration by terrestrial mammals especially—to serve as vehicles of communication into the future. This function whereby an individual can leave messages for another to find in his absence or, by a delayed feedback loop, even leave messages for himself, is analogous to the human use of script (Haldane 1955). Its overwhelming evolutionary value is confirmed by the fact, for example, that herbivores usually leave telltale trails, at the risk of revealing their whereabouts to carnivores, while some of the latter broadcast a strong smell advertising their presence, at the sacrifice of part of the surprise element in hunting.

Optical systems (Marler 1961b; Wynne-Edwards 1962, chapter 2; Tinbergen 1964) presuppose reflected daylight in the case of diurnal species and bioluminescence (McElroy & Seliger 1962) in those species that dwell in dark but transparent media. Patterns of visual activity are highly variable as to shape and color, duration, and range of intensity; they can also be actively displayed by movements and postures, as in three-spined sticklebacks (Tinbergen 1953a); by facial expressions, as in the primates (Andrew 1964); or by intermittent flashing, as in fireflies. Thus, visual signs are both flexible and transient: they can be rapidly switched on or off. These capacities allow for precise coding of information and may even be exploited to misdirect, as in protective displays involving “eyespots” in moths (Blest 1957). Ethologists, concerned with the origin and evolution of visual and other forms of signaling behavior, have described and provisionally classified them into three principal categories: movements signifying intention, that is, those which seem to be preparatory or incomplete versions of functional acts (such as choking in kittiwakes); autonomic effects (such as piloerection in dogs); and so-called displacement movements, that is, those which appear to be irrelevant in the context in which they are delivered (such as preening in pigeons during courtship). Ethologists think that there has been an evolutionary process of increased adaptation to visual signaling behavior; they call this modification ritualization.

Tactile systems include rather disparate phenomena, from all sectors of the animal world. They all have in common the requirement that the individuals communicating by such means must be in physical contact: suckling, copulating, fighting, social grooming or mutual preening. Although communication in this channel is thereby limited to relatively short distances, its effective range can be increased somewhat by the use of elongated feelers, such as antennae, tentacles, barbels, fin rays, or the like, and considerably further by, for example, lines of silk, as in many spiders (Wynne-Edwards 1962, chapter 7). Since tactile signals are subject to wide variations in duration and intensity, they are particularly useful for the transmission of quantitative information, such as distances. The nature of topographic discriminations achieved through an animal’s body surface or through more or less sensitive contact receptors is not well understood; the possibilities of cutaneous message processing are, however, being explored (Geldard 1960).

Partly because it has an immediate appeal to the imagination of men and partly because it was stimulated by technological refinements that became available in the decades after World War ii, the study of the mechanical vibrations by which some animals communicate constitutes one of the most advanced branches of zoosemiotics (Symposium on Animal Sounds and Communication I960; Busnel 1963). Bioacoustical systems may operate in the air, as with insects and with birds, which as a class are the most vocal of animals. The mammals that communicate this way are the bats (Griffin 1958), shrews, rodents, deer, seals (Bartholomew & Collias 1962), the carnivores, especially Felidae (Moelk 1944) and Canidae (Hafez 1962, pp. 442–443), and the monkeys and anthropoid apes (Yerkes & Learned 1925; Altmann 1966). Bioacoustical systems for social communication and display may also operate underwater (Wynne-Edwards 1962, chapter 4; Symposium on Marine Bio-acoustics 1964) and have been variously recognized among Crustacea, aquatic insects, fishes, and Cetacea; in recent years whale communication has been receiving increased attention (Sebeok 1963a). Finally, rhythmic changes of density in a solid may also form an acoustical system, e.g., the quacks of queen honeybees are transmitted directly through the hive material (Wenner 1962). Although both visual and auditory perception occur in space and time, vision is pre-eminently the spatial sense, just as audition is the temporal. In acoustic communication, reaction times are typically fast (the speed of response in the avian ear is estimated to be about ten times that in the human: Thorpe 1963a) and sound signals can be received at as great distances as chemical ones. The emission of sounds involves a minute output of energy, and their transient character makes accurate timing possible. If perceived by the proper receiving organs, sounds—especially those in the higher frequencies—can be directional, when it is advantageous that information about the sender’s location be broadcast; on the other hand, with the use of lower frequencies the sender’s whereabouts may be kept concealed. Sound fills the entire space around the source and therefore does not require a straight line of connection with the receiver: a signal can travel around corners and is not usually interrupted by obstacles. This flexibility in frequencies, intensities, and patterns is important in that it allows for considerable specific differentiations, as well as, within a species, for individual variation with many shadings and emphases.

Echolocation—where the encoder and decoder of an acoustic (or, sometimes, electrically coded) message is the same living animal in a situation of rapid feedback—may be regarded as a special case of communication. This phenomenon was first discovered in bats (Griffin 1958) but has since been found in all sorts of other animals, including gyrinid beetles, the South American oilbird, the southeast Asian swiftlet, and some seals and porpoises (Kellogg 1961). It has also been shown that moths of the family Arctiidae emit noisy ultrasonic pulses when they detect insectivorous bats pursuing them and that these bursts may function to mislead their predators (Dunning & Roeder 1965).

It is well known that certain fishes generate electric fields. It seems probable that some of the feebler impulses are employed for signaling, at least in those species (such as a number of mormyrids and gymnotids) where the frequencies and patterns of discharge are distinct (Wynne-Edwards 1962, chapter 5). Such electric rhythms have even been compared to the song displays of birds and ascribed an analogous territorial function. While it is suspected that thermal sensation, also, is employed as a communication channel among certain animals, there is as yet insufficient evidence to substantiate this.

Matter, as well as energy, may serve as a message conductor, as in honeybees, ants, and termites, where processes that bring food and water also transport information vital to the survival of the colony. This form of semiotic biosocial facilitation of interindividual stimulative relationships is known as trophallaxis (Wheeler 1926; Lindauer 1962).

Context and significance of signals

Although it is both necessary and proper to distinguish the several channels of animal communication and to study each in isolation, the redundancy that prevails among the multiplicity of bands in natural systems—an effect sometimes referred to as the law of heterogeneous summation—must soon become an object of both theoretical and practical concern. The over-all code that regulates an animal communication network often seems to consist of a set of subcodes grouped in a hierarchy. Fluctuations that occur in these subcodes are determined by such factors as the kind of information to be transmitted, the availability of alternative channels, and the distance between source and receiver. Thus, in the mountain gorilla, vocalizations employed when the individual is hidden from view by dense vegetation serve to draw attention to the animal emitting them; these sounds notify other gorillas of the specific emotional state of the performer and alert them to watch for gestures, which then communicate further information. Postures and gestures, especially facial expressions, coordinate behavior within the group when the distance between the members decreases; the visual subcode is in turn replaced by the tactile subcode when distance is still further diminished, as between a female and her small infant (Schaller 1963).

In each species the source of a message must share a code with its destination. This is the critical element of communicative commerce; it constitutes a particularized version of the universal “need to know.” Every emitting organism’s selection of a message out of its species-consistent code, as well as the receiving organism’s apprehension of it, proceeds either in accordance with a “closed” genetic program, automatically and predictably shaping a wholly prefabricated set of responses, or with reference to the animal’s unique memory store, which then directs the way in which the genetically precoded portion of the total behavior program is acted out. Even in “open” behavior programs certain releaser mechanisms can begin to function only at predetermined stages of maturation. The relationship of learning to instinct in animals in general has been reviewed by Thorpe (1963b), and the relative influence of inheritance and learning in the development of vocalizations by Marler (1963), while the question of learning from alien species, especially the capacity of certain birds and mammals to imitate human speech—the phenomenon of mimicry—has been examined by Andrew (1962). As one would expect, the higher vertebrates tend to be increasingly malleable through learning experience—certain domesticated species can even be motivated by verbal instruction (elephants, for example, can be trained to distinguish between up to 24 different commands by purely auditory perception).

The basic assumption of zoosemantics is that in the last analysis all animals are social beings, each species with a characteristic set of communication problems to solve. All organic alliances presuppose a measure of communication: protozoa interchange signals; an aggregate of cells becomes an organism by virtue of the fact that the component cells can influence one another. Creatures of the same species must locate and identify each other; moreover, they must convey information as to what niche they occupy, in territory as well as status, in the social hierarchy and also as to their momentary mood. Intraspecific and interspecific messages furthering ends such as these can be coarsely categorized in terms of their ecological or functional contexts, and different scholars have devised roughly comparable, but all more or less subjective, schemes to classify the supposed signification of the signals they have observed. Thus, it is possible to note intraspecific expressions of threat, warning, fear, pain, hunger, and—at least in the highest of animals—such feelings as defiance, well-being, superiority, elation, excitement, friendliness, submission, dejection, and solicitude and interspecific warning signals, intimidating signals, decoying signals, and positive or negative masking signals (Wynne-Edwards 1962, pp. 24–25). Frings and Frings (1964) have noted species identification in aggregational systems (cellular, sessile, mobile, social, and interspecific) and dispersal systems (ritualized fighting, aggressive displays, and territorial behavior); social cooperation, involving such items of information as alarm signals (subclassified as indicators of departure, distress, warning, and the like) and food signals; sexual attraction and recognition; courtship and mating; and communication in the parent-young relationship. Collias (1960, p. 387) relates all acoustic messages to five contexts: food gathering, predatism, sexual and allied fighting behavior, parent–young interrelations, and aggregations and group movements. Armstrong, with due cautioning about difficulties and uncertainties, lists the categories required to cover the range of context in the auditory communication of birds (see Table 1).

The associative ties between signals and their meanings are often arbitrary (as opposed to iconic): thus, tail movements in a dog denote friendship; in a cat, hostility; and in a horse, the presence of flies. Some signals are “shifters” (Sebeok 1965a), whose meaning differs according to the situation: thus, the honeybee’s tail-wagging dance has more than one denotatum, for it designates either a food source or a nesting site; the gesture pattern is identical, its pragmatic import depending, not upon variation in the form of the expression, but solely upon the attendant physical context. The herring gull’s head tossing has more than one function: it occurs as a precoital display, but this is indistinguishable from the head tossing exhibited by a female begging for food (Tinbergen [1953b] 1961, p. 112).

The importance of compiling a complete inventory of the behavior of every species studied has been stressed by, among others, Tinbergen (1951), who called collections of raw materials of this sort “ethograms.” An ethogram should, of course, incorporate a description of the zoosyntactic properties of the codes peculiar to each species. In this respect an ethographer plays the role of a crypt-analyst, receiving messages not destined for him and ignorant of the pertinent transformation rules. Although there are perhaps 700,000 animal species extant, virtually none of the codes in use is fully understood, not even the one regulating the remarkable communication system honeybees have developed. While the fact that these bees perform intricate movements—the famous “dances”—in directing their hivemates to a source of food supply or to new quarters has been widely reported and is now a familiar story, it is not so well known that these insects transmit information through acoustic means as well. It has been amply demonstrated that the length of the train of sound emitted during the straight run of the dance tells the distance of the find (Wenner 1964), but this discovery is bound to be only a first step in the comprehensive unfolding of the auditory subcode of the bees; researchers in several laboratories are now investigating this hardly anticipated facet of the apiarian ethogram.

Following certain distinctions noted by Morris (1946, pp. 219–220), it seems useful to mark three possible approaches to zoosemiotics: pure, descriptive, and applied.

Pure zoosemiotics is concerned with the elaboration of theoretical models or, in the broadest sense, with the development of a language designed to deal scientifically with animal signaling behavior.

Descriptive zoosemiotics comprehends the study of animal communication as a natural and as a behavioral science, in its pragmatic, semantic, and syntactic aspects, as briefly outlined in this article.

Finally, applied zoosemiotics aims to deal with the exploitation of animal communication systems for the benefit of man. Utilitarian applications— tasks, in the main, for the future—may be confidently envisaged in wildlife management (e.g., control of the coyote by input of its own or its prey’s distress calls); agriculture (e.g., pollination of orchard trees by electronically programmed bees); and pest control (e.g., the prevention of woodpecker damage to wooden utility poles by use of repellent chemical and auditory signals). Our knowledge of basic zoosemiotic processes may also be put to practical uses to supplement existing human information-handling devices (in aiding the deaf and the blind, in assisting communication with man in outer space), and to advance bionics, the science of converting living systems into mechanical and electrical analogues. Linguists and psycholinguists who are concerned with animal communication are interested chiefly in disclosing the biological and anthropological origins of human communication. They seek answers to particular questions such as these: what are the anatomical and physiological correlates of verbal behavior and what sensory and cognitive specializations are required for language perception? what motivates the onset and accomplishment of language learning in the development of human infants? why do subhuman forms lack the capacity to acquire even the beginnings of language? how can present evolutionary theory account for the unique form and behavior of language in man? what is the genetic basis for language propensity, man’s species-specific biological endowment? Zoosemiotics, although still in its infancy, provides the scientist with a simpler setting in which to search for solutions than does the far more complex sociobiological environment that constitutes the framework of man’s communicative behavior.

Thomas A. Sebeok

[See alsoEthology; Semantics and semiotics; Social behavior, animal.]

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