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