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A discipline within the field of animal behavior that focuses upon the reception and use of signals. Animal communication could well include all of animal behavior, since a liberal definition of the term signal could include all stimuli perceived by an animal. However, most research in animal communication deals only with those cases in which a signal, defined as a structured stimulus generated by one member of a species, is subsequently used by and influences the behavior of another member of the same species in a predictable way (intraspecific communication). In this context, communication occurs in virtually all animal species.
The field of animal communication includes an analysis of the physical characteristics of those signals believed to be responsible in any given case of information transfer. A large part of this interest is due to technological improvements in signal detection, coupled with analysis of the signals obtained with such devices.
Information transmission between two individuals can pass in four channels: acoustic, visual, chemical, and electrical. An individual animal may require information from two or more channels simultaneously before responding appropriately to reception of a signal. Furthermore, a stimulus may evoke a response under one circumstance but be ignored in a different context.
Acoustic signals have characteristics that make them particularly suitable for communication, and virtually all animal groups have some forms which communicate by means of sound. Sound can travel relatively long distances in air or water, and obstacles between the source and the recipient interfere little with an animal's ability to locate the source. Sounds are essentially instantaneous and can be altered in important ways. Both amplitude and frequency modulation can be found in sounds emitted by animals; in some species sound signals have discrete patterns due to frequency and timing of utterances. Since a wide variety of sound signals are possible, each species can have a unique set of signals in its repertoire. See Phonoreception
Sound signals are produced and received primarily during sexual attraction, including mating and competition. They may also be important in adult–young interactions, in the coordination of movements of a group, in alarm and distress calls, and in intraspecific signaling during foraging behavior. See Reproductive behavior
Visual signaling between animals can be an obvious component of communication. Besides the normal range of human vision (visible light), visual signals include additional frequencies in the infrared and ultraviolet ranges. The quality of light that is often considered is color, but other characteristics are important in visual communication. Alterations of brightness, pattern, and timing also provide versatility in signal composition. The visual channel suffers from the important limitation that all visual signals must be line of sight. Information transfer is therefore largely restricted to the daytime (except for animals such as fireflies) and to rather close-range situations.
Intraspecific visual signaling appears to occur primarily during mate attraction. The color dimorphism of birds, the patterns of butterfly wings, the posturing of some fish, and firefly flashing are examples. Some parent--young interactions involve visual signaling. A young bird in the nest may open its mouth when it sees the underside of its parent's beak. Other examples are the synchronized behavior observed in schooling fish and flocking birds.
Chemical signals, like visual and sound signals, can travel long distances, but with an important distinction. Distant transmission of chemical signals requires a movement of air or water. Therefore, an animal cannot perceive an odor from a distance; it can only perceive molecules brought to it by a current of air or water. Animals do not hunt for an odor source by moving other than upwind or upcurrent in water because chemical signals do not travel in still air or water since diffusion is far too slow.
The fact that chemical signals comprise molecules means that, unlike acoustical or visual signals, chemical signals have a time lag. Chemical signals have to be of an appropriate concentration if they are to be effective. A chemical normally considered to be an attractant can serve as a repellent if it is too strong. Chemical signals may persist for a while, and time must pass before the concentration drops below the threshold level for reception by a searching animal. Since molecules of different sizes and shapes have varying degrees of persistence in the environment, the chemical channel is often involved in territorial marking, odor trail formation, and mate attraction. This channel is particularly suitable where acoustical or visual signals might betray the location of a signaler to a potential predator.
The array of molecular structure is essentially limitless, permitting a species-specific nature for chemical signals. Unfortunately, that specificity can make interception and analysis of chemical signals a difficult matter for research.
Pheromones are chemical signals that are produced by an animal and are exuded to influence the behavior of other members of the same species. If pheromones are incorporated into a recipient's body (by ingestion or absorption), they may chemically alter the behavior of such an individual for a considerable period of time. See Chemical ecology, Chemoreception, Pheromone
Some electric fish and electric eels live in murky water and have electric generating organs that are really modified muscle bundles. Communication by electric signaling is rapid; signals can travel throughout the medium (even murky water), and rather complex signals can be generated, permitting species-specific communication during sexual attraction. However, the electrical mode is apparently restricted to those species that have electric generating organs.
Animal communication is one of the most difficult areas of study in science for several reasons. First, experiments must be designed and executed in such a manner that extraneous cues (artifacts) are eliminated as potential causes of the observed results. Second, once supportive evidence has been obtained, each hypothesis must be tested. In animal communication studies, adequate tests often rely upon direct evidence—that is, evidence obtained by artificially generating the signal presumed responsible for a given behavioral act, providing that signal to a receptive animal, and actually evoking a specific behavioral act in a predictable manner. See Ethology, Psycholinguistics
communication by means of signals between animals of the same or different species. Animals communicate with specific chemical, mechanical, optical, auditory, and electrical signals, as well as with nonspecific signals that accompany respiration, locomotion, or feeding. The signals are received by means of the organs of sight, hearing, olfaction, taste, and skin sensitivity; lateral-line organs (in fish); thermoreceptors; and electroreceptors.
The generation and reception of signals form communication channels (auditory, chemical) between organisms for the transmission of information of varying physical or chemical nature. Information entering through different channels of communication is processed in different parts of the nervous system and is then integrated in the higher nerve centers, where the response reaction of the organism is formed.
Animal communication facilitates the search for food and favorable living conditions and protects an animal from enemies and other dangers. Without communicatory signals, courtship and mating, care of the young, formation of groups (flocks, herds, hives, colonies), and regulation of relationships between individuals in a group (territoriality, hierarchy) would be impossible.
The role of one or another channel of communication is not identical in all animals and is determined by the ecology and morphophysiology of a species, which were established in the course of evolution. It also depends on changing environmental conditions and biological rhythms. As a rule, animals simultaneously use several communication channels.
The most ancient and widespread channel of communication is chemical. Certain metabolic products discharged by an animal act on the chemical sense organs—of olfaction and taste—and regulate the growth, development, and reproduction of organisms. They also act as signals that produce definite behavioral reactions in other individuals. The pheromones of certain male fishes accelerate female maturation, thus synchronizing reproduction of the population. Odorous substances discharged into the air or water, as well as on the ground or on various objects, mark an animal’s territory, facilitate orientation, and strengthen communications between members of a group. Fish, amphibians, and mammals readily distinguish the odors of individuals of their own and other species, while common group odors enable animals to distinguish “their own” from “strangers.”
Aquatic animals communicate principally by means of lateral-line organs, which receive vibrations in the water. This form of mechanical reception over distances enables an animal to recognize an enemy or prey and maintains order within the group.
Tactile communicatory signals, such as the mutual grooming of plumage or fur, are important in regulating intraspecific relationships in some birds and mammals. Females and subordinate individuals usually groom the dominant individuals (mainly adult males). The electrical fields produced by electric fish, lampreys, and hagfishes serve as territorial markers and aid in short-range orientation and in the search for food. Among nonelectric schooling fish a common electric field is created, which coordinates the behavior of individuals.
Visual animal communication, related to the development of vision and light sensitivity, is associated with the development of special features that serve as signals (coloration, patterns, contours of the body and its parts) and with the origin of ritual movements and facial expressions. The process of ritualization, that is, the formation of discrete signals, each of which is associated with a particular situation and has a conventional meaning (threat, subordination, appeasement), decreases the danger of intraspecific conflict. For example, bees that have discovered nectar-bearing plants inform other bees as to the location and distance of the food by means of a dance. (This subject is dealt with in the works of the German physiologist K. von Frisch.)
For many species, ethograms—complete catalogs of the language of poses, gestures, and facial expressions—have been compiled. Communication often involves disguising or exaggerating one or another feature of coloration or shape. Visual communicatory signals play a particularly important role among animals in open terrain (steppes, deserts, tundras); their significance is substantially less among aquatic animals and inhabitants of thickets.
Auditory communication is most highly developed in arthropods and vertebrates. Its role as an effective means of remote signaling increases in an aquatic medium and in closed terrain (forests and thickets). The development of auditory communication depends on the state of other channels of communication. In birds, for example, high auditory abilities primarily characterize modestly colored species, while species with bright coloration and complex demonstrative behavior have a low level of auditory communication.
The differentiation of complex sound-producing features in many insects, fishes, amphibians, birds, and mammals enables them to produce dozens of varied sounds. Songbirds produce as many as 30 basic signals that are combined in various ways, thus increasing the range of communication. Such a broad range of signals makes it possible for a bird to recognize its mate or a member of its flock. In a number of bird species, auditory contact between parents and offspring is established even before the young are hatched from the egg. A comparison of variations of visual signaling in crabs and ducks with variations of auditory signaling among birds reveals similarities between different types of signaling. Apparently, the capacities of the visual and auditory channels of communication are comparable.
Each animal species has a specific signaling system, made up of a complex of signaling features and specific behavioral reactions. Studies show that fish have from ten to 26 specific signals, birds 14 to 28, and mammals ten to 37. Phenomena similar to ritualization may also develop in the evolution of interspecific communication. As protection against predators that hunt their prey by odor, prey species discharge repellent odors and develop inedible tissues. To escape from predators that hunt by sight, some species exhibit repellent coloration.
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N. P. NAUMOV