Communication (zoology)

A simple definition of animal communication is the transmission of information between animals by means of signals. Developing a more precise definition is difficult because of the broad array of behaviors that are considered messages or signals and the variety of contexts in which these behaviors may occur. Animal signals can be chemical, visual, auditory, tactile, or electrical. The primary means of communication used within a species will depend upon its sensory capacities and its ecology.

Pheromones

Of the modes of communication available, chemical signals, or pheromones, are assumed to have been the earliest signals used by animals. Transmission of chemical signals is not affected by darkness or by obstacles. One special advantage is that the sender of a chemical message can leave the message behind when it moves. The persistence of the signal may also be a disadvantage when it interferes with the transmission of newer information. Another disadvantage is that the transmission is relatively slow.

The speed at which a chemical message affects the recipient varies. Some messages have an immediate effect on the behavior of recipients. Alarm and sex-attractant pheromones of many insects, aggregation pheromones in cockroaches, or trail substances in ants are examples. Other chemical messages, primers, affect recipients more slowly through physiological changes. Examples of primers include pheromones that control social structure in hive insects such as termites. Reproductive members of the colony secrete a substance that inhibits the development of reproductive capacity in other hive members. The chemicals that control the hive are spread through grooming and food sharing (trophallaxis). Chemical communication is important not only among social and semisocial insects but also among animals, both vertebrates and invertebrates. Particularly common is using a pheromone to indicate that an animal is sexually receptive.

Visual Signals

Visual communication holds forth the advantage of immediate transmission. A visual signal or display can also encode a large amount of information, including the location of the sender. Postures and movements of parts of an animal’s body are typical elements of visual communication. Color and timing are additional means of providing information. Some visual signals are discrete; that is, the signal shows no significant variation from performance to performance. Other displays are graded so that the information content of the signal can be varied. An example of a graded display is found in many of the threatening or aggressive postures of birds. Threat postures of the chaffinch vary between low-intensity and high-intensity postures. The elevation of the crest varies in ways that indicate the bird’s relative readiness for combat. The song spreads of red-winged blackbirds and cowbirds show variation in intensity. In red-winged blackbirds, the red epaulets, or shoulder patches, are exposed to heighten the effect of the display. Discrete and graded signals may be used together to increase the information provided by the signal. In zebras, ears back indicate a threat, and ears up indicate a greeting. The intensity of either message is shown by the degree to which the mouth is held open. A widely open mouth indicates a heightened greeting or threat.

Visual displays depend upon the presence of light or the production of light. The ability to produce light, bioluminescence, is found most frequently in aquatic organisms, but its use in communication is probably best documented in fireflies, beetles belonging to the family Lampyridae. Firefly males advertise their presence by producing flashes of light in a species-specific pattern. Females respond with simple flashes, precisely timed, to indicate that they belong to the appropriate species. This communication system is used to advantage by females in a few predatory species of the genus Photuris. After females of predatory species have mated with males of their own species, they attract males of other species by mimicking the responses of the appropriate females. The males that are tricked are promptly eaten. The luminescence of fireflies does not attract a wide variety of nocturnal predators because their bodies contain a chemical that makes them unpalatable.

Visual displays are limited in the distance over which they can be used and are easily blocked by obstacles. Visual communication is important in primates, birds, and some insects but can be dispensed with by many species that do not have the necessary sensory capacities.

Auditory Communication

The limitation of visual communication is frequently offset by the coupling of visual displays with other modes of communication. Visual displays can be coupled with auditory communication, for example. There are many advantages to using sound: It can be used in the dark, and it can go around obstacles and provide directional information. Because pitch, volume, and temporal patterns of sound can be varied, extremely complex messages can be communicated. The auditory communication of many bird species has been studied intensively. Bird vocalizations are usually classified into two groups, calls, and songs. Calls are usually brief sounds, whereas songs are longer, more complex, and often more suited to transmission over distances.

The call repertoire of a species serves a broad array of functions. Many young birds use both a visual signal, gaping, and calling in their food begging. Individuals that call more may receive more food. Begging calls and postures may also be used by females in some species to solicit food from mates. One call type that has been intensively studied is the alarm call. Alarm calls of many species are similar, and response is frequently interspecific (that is, interpretable by more than one species). Alarm calls are likely to be difficult to locate, a definite advantage to the individual giving the call. Calls used to gather individuals for mobbing predators are also similar in different species. Unlike alarm calls, mobbing calls provide good directional information so that recruitment to the mobbing effort can be rapid.

Call repertoires serve birds in a great variety of contexts important for the survival of the individual. Song, on the other hand, most often serves a reproductive function, that of helping a male hold territory and attract a mate. Songs are species-specific, like the distinctive markings of a species. In some cases, songs are more distinctive than their physical appearance. The chiffchaff and willow warbler were not recognized as separate species until an English naturalist named Gilbert White discovered, by examining their distinctive songs, that they are separate. The North American wood and hermit thrushes can also be distinguished more readily by song than by appearance. Bird songs can communicate not only the species of the individual singing but also information about motivational state. Most singing is done by males during the breeding season. In many species, only the male sings. In some species, females sing as well. Their songs may be similar to the songs of the males of their species, or they may be distinctive. If the songs are similar to those of the males, the female may sing songs infrequently and with less volume. In some instances, the female song serves to notify her mate of her location. An interesting phenomenon found in some species is duetting, in which the male and female develop a duet. Mates may sing in alternate and perfectly timed phrases, as is done by the African boubou shrike, Laniarius aethiopicus. An individual shrike can recall its mate by singing the entire song alone.

Individuals in some bird species have a single song, and individuals of other species have repertoires of songs. The average repertoire size of the individual is characteristic of a species. Whether songs in repertoires are shared with neighbors or unique to the individual is also characteristic of a species. Sharing songs with neighbors permits song matching in countersinging. Cardinals and tufted titmice are species that frequently match songs in countersinging. Possible uses for matching are facilitating the recognition of intruders and indicating which neighbor has the attention of a singer. Some species of birds have dialects. The species-specific songs of one geographic region can be differentiated from the song of another geographic region. The development of dialects may be useful in maintaining local adaptations within a species, provided that females select mates of the same dialect as their fathers.

Although auditory signals of birds have received a disproportionate share of attention in the study of animal communication, auditory communication is used by a broad spectrum of animals. Crickets have species-specific songs to attract females and courtship songs to encourage an approaching female. The ears of most insects can hear only one pitch, so the temporal pattern of sound pulses is the feature by which a species can be identified. Vervet monkeys use three different alarm calls, depending upon the kind of threat present; they respond to the calls appropriately by looking up, looking down, or climbing a tree, depending upon the kind of call given.

Tactile and Electrical Communication

Tactile communication differs significantly from other forms of communication in that it cannot occur over a distance. This form of communication is important in many insects, equipped as they are with antennae rich in receptors. Shortly after a termite molts, for example, it strokes the end of the abdomen of another individual with its antennae and mouthparts. The individual receiving this signal responds by extruding a fluid from its hindgut. Tactile signals are frequently used in eliciting trophallaxis (food sharing) in social insects. Tactile signals are also important in the copulatory activity of several vertebrates.

Additional channels of communication available in animals are electrical and surface vibration. Many modes of communication are used in combination with other modes. The channels used will depend in part on the sensory equipment of the species, its ecology, and the particular context. Most messages will be important either for the survival of the individual or the group or for the individual’s ability to transmit their genes to the next generation.

Communication Studies

The early study of animal communication depended primarily on the careful observation of animals. This technique has been supplemented by several tools. High-definition cameras permit the observer to analyze visual displays more completely. Auditory recorders are a particularly versatile tool; acoustical communication can be recorded, and the result is used in playback experiments, in which the ethologist plays the recording in the field to test hypotheses about communication. Playbacks have helped scientists determine that some species of birds can discriminate between the songs of neighbors and the songs of strangers. Taped songs have been cut and spliced in various sequences to determine which features of a song’s structure are important in species recognition.

The development of song in some species has been studied by means of isolation experiments. Birds that have been hatched and reared in the laboratory have been isolated from their species-specific song to determine whether the song needs to be learned. Some isolates are exposed to tutors (either tape recordings or living birds) at various intervals to examine the possibility of critical periods for song learning.

Sound spectrographs make it possible to produce pictures of calls and songs. Spectrographs represent song frequency on one axis and time on the other. These graphs have revealed the intricate structures of many auditory communication signals.

Information about sensory reception and about neural control of signals is an important research area. Some information in this area has come from ingenious but simple experiments. Bees have been trained to respond to color clues in association with a sugar source to determine which colors they can discriminate. Important knowledge in sensory research comes from determining the specific stimuli that will elicit a response in specific neurons. By using microelectrodes placed in or near the neuron, scientists can detect the presence of a response. Another technique used to determine the function of a presumed sense organ is to block or remove either the organ or the neural connections to the organ. One of the earliest experiments of this type was done in 1793 by Lazzaro Spallanzani. He found that flying bats could not avoid obstacles when their ears were tightly plugged but that the bats were able to avoid obstacles when they were blinded. In 1938, the use of an ultrasonic recorder made it possible for Donald Griffin to discover the bat’s use of ultrasonic sound.

Synthetic pheromones can be produced that have the same effects on behavior as natural pheromones. Scientists can also determine at what dilution a pheromone will still evoke a response. Hence, the sophisticated tools of chemistry have important applications in ethology.

Talking to Animals

Animal communication provides a fascinating frontier for exploration. Some of the knowledge acquired has had practical applications as well. Pheromones have been used to bait traps for insect pests. In some cases, this technique is used directly as a control measure; in other instances, the traps are used to estimate population size and other control measures are used when pest populations are high. A key advantage of pheromone use is its specificity.

Recognizing the communication signals of pets and domestic animals is often useful in their care. Knowledge of releasers, standard signals that receive standard animal responses, is important for survival in some contexts. Knowing which signals are perceived by animals as threats allows humans to avoid triggering an attack. This knowledge also allows the control of animals in less destructive ways. Recordings of alarm signals of birds are used to disperse flocks that are creating problems.

Knowledge of a species’ communication repertoire is critical in the training of animals for useful work or for entertainment. Also, knowledge of their sensory capacities makes it possible for appropriate signals to be selected—particularly important as it applies to human nonverbal communication. Knowing which signals of our nonverbal communication repertoire are characteristic of the whole species is both useful and interesting.

Principal Terms

Discrete Signals: signals that are always given in the same way and indicate only the presence or absence of a particular condition or state

Display: a term used to indicate social signals, particularly visual signals

Pheromone: a chemical substance used in communication within a species

Primer Pheromone: a chemical substance that affects behavior by altering physiology and is therefore not rapid in its effects

Releaser: a standard signal that elicits a standard response

Trophallaxis: food exchange between organisms, particularly in social insects

Bibliography

“Auditory Communication - NatureWorks.” New Hampshire PBS, 2023, nhpbs.org/natureworks/nwep3b.htm. Accessed 9 July 2023.

Bradbury, Jack W., and Sandra L. Vehrencamp. Principles of Animal Communication. 2nd ed. Sunderland: Sinauer, 2011. Print.

De Waal, Frans. Chimpanzee Politics: Power and Sex among Apes. 25th anniversary ed. Baltimore: Johns Hopkins UP, 2007. Print.

Goodall, Jane. In the Shadow of Man. Rev. ed. Boston: Houghton, 2009. Print.

Grier, James W. Biology of Animal Behavior. 3rd ed. New York: McGraw-Hill, 1999. Print.

Hart, Stephen. The Language of Animals. New York: Holt, 1996. Print.

Hauser, Marc D. The Evolution of Communication. Cambridge: MIT P, 1996. Print.

Roitblat, Herbert L., Louis M. Herman, and Paul E. Nachtigall, eds. Language and Communication: Comparative Perspectives. Hillsdale: Erlbaum, 1993. Print.

Wilson, Edward O. Insect Societies. Cambridge: Harvard UP, 1971. Print.