Ethology

BIBLIOGRAPHY

Ethology has existed as a concept since 1762 when it was defined in France as the study of animal behavior. In this sense it carries the same meaning as the Greek word “ethos,” from which the modern term ethology is derived. However, a separate meaning of the word ethology, related to the term “ethics,” has been used in the Anglo-Saxon literature to define the “science of character.”

The founder of modern ethology is Konrad Z. Lorenz, physician, zoologist, and comparative anatomist. By systematic application of biological research methods to the analysis of animal behavior, he provided the initial impetus in the 1930s. The first modern ethology textbook, The Study of Instinct, was written by Nikolaas Tinbergen in 1951, and E. H. Hess (1962) and Eibl-Eibesfeldt (1966) recently produced summaries of the modern concepts of behavior. The observations of a number of pioneers, including Spalding (1873), Darwin (1872), Whitman (1898), Altum (1868), Heinroth (1911), and Craig (1918), awakened scientific interest in animal behavior, and ethology came to be considered an independent branch of zoology around 1910. As with every young science, ethology inevitably suffers, on the one hand, from the incorporation of concepts whose meaning has oscillated or has already become too specialized (such as “instinct”) and, on the other hand, from the application of provisional concepts, which may alter in meaning with advances in knowledge, to contemporary working hypotheses.

The term “ethology” is now attached to the scientific investigation of the behavior of animals and of some aspects of human behavior. Pronouncements about inaccessible psychic phenomena are avoided; the term “animal psychology” is still occasionally used but on purely historical grounds. Ethology is concerned with the investigation of animals, whether these be single cells–either as individual protozoans or as parts of metazoans– or more complex animal structures, that is, individuals, groups, or so-called animal colonies (e.g., ants, bees, and termites).

The behavior of an animal is equated with changes brought about by effectors (e.g., movements, sounds, scent production, color changes). Such effector responses are temporal events. For this reason only effector responses which repeatedly and identifiably occur are open to scientific analysis; they are then termed “fixed action patterns.” It is important to note that these temporal events can be recorded by tape and film, except in the case of chemical or tactile signals. The locomotion of an animal can be subdivided into the movement of the extremities, of antagonistic muscle groups, of single muscles, and ultimately of the muscle fibers. The smallest identifiable effector components, occurring either singly or in combination with other components, are chosen as the units of ethological study.

The aim of ethology is to explain both phylogenetically and physiologically the functional relationships of all factors involved in behavior. This is evident in the modern definition of instinct suggested by Tinbergen: “… a hierarchically organized nervous mechanism which is susceptible to certain priming, releasing and directing impulses of internal as well as of external origin, and which responds to these impulses by coordinated movements that contribute to the maintenance of the individual and the species” (1951, p. 112). The touchstone for ethological hypotheses is the reliable prediction of the behavior of a living system in any given situation.

Ethologists are zoologists; they are thus interested in the biology of a species, and their prime interest is behavior as it occurs under natural conditions. The ethologist always begins by compiling an “action catalogue,” or ethogram of the species in question, that is, as complete a description as possible of the behavior throughout the animal’s life cycle. This simply describes what the animal does, not why it does it.

The various behavior patterns are then classified and compared with those of other species, especially with closely related species. It is important that the animals should be observed in their natural habitats or in surroundings which closely resemble them. Additional observations in captivity are often necessary. A very useful expedient, first known to have been practiced by Baron Ferdinand Adam von Pernau in 1702, is to rear the animals to be both tame and unconfined.

Learning, maturation, and genetics. Although learning is considered to be very important in animal behavior, the first concern of the ethologist is with behavior patterns typically performed by all animals of a species, because it is necessary for him to know the basic predetermined responses before proceeding to study changes brought about by learning. This is important, since not every change of form or effectiveness of a given behavior pattern occurring during the life of an individual involves learning in the form of acquisition by experience. As early as 1760 a professor in Hamburg, Hermann Samuel Reimarus, discovered the phenomenon of maturation of instincts and pointed out the difference between innate and acquired skills. The innate skills, for example, the collection of food or the performance and “understanding” of the dance language in bees, are present from the time of birth or of hatching from the egg or pupa. Without involving a definition of learning, the problem can be formulated as follows: the majority of behavior patterns in most animals are adapted (adjusted) to special situations in their respective environments. Since this fact cannot be explained as a chance phenomenon and since it is not a self-evident phenomenon, an explanation must be provided. In order to behave adaptively, the animal must have at its disposal information about the environment. This information can be stored either in the chromosomes or in memory; that is, it can be either innate or acquired. In complex behavior patterns, there is often an interaction between innate and acquired elements. However, although we know of perceptual and motor skills in which learning plays no part, it is impossible to postulate a completely learned element of behavior that is not based on genetically determined and, therefore, delimited capabilities. Further, no one has so far been able to demonstrate the infinite modifiability of any arbitrarily chosen, innately determined element of behavior or the possibility that learning could be the function of a nonorganized aggregate of neural elements. In learning, the fact that the organism selects “good” and not “bad” behavioral responses or stimuli logically implies a built-in mechanism which is able to direct learning toward survival value.

A particularly good method for distinguishing between the learned and innate elements of behavior is contained in the deprivation experiment: the animal, usually isolated from members of its own species, is deprived of certain experiences and later tested in the situation to which the behavior pattern in question is normally adapted. As a control a normal animal must be tested in the same situation. (This is one of several safety precautions which are necessary in the evaluation of the deprivation experiment.) The majority of behavior patterns do not follow the all-or-none law but can occur at varying intensities. The lowest intensities, where it is just possible to recognize which pattern has been activated, are referred to as intention movements. The intensity with which a behavior pattern is performed depends upon both internal and external factors.

The appearance of a particular fixed action pattern in animals isolated from their own species is clear evidence of genetic fixity. It is a constant characteristic of the species concerned and is based upon a specific central nervous mechanism that is inherited just as are morphological and physiological characteristics. (This had already been stated by the English naturalist Spalding in 1873.) A particularly good example is provided by many bird songs which develop into the species-specific pattern even in completely isolated animals. Research into the genetic basis of behavior patterns is developing as an important part of ethology. For example, crossing two duck species which differ in their courtship behavior can give rise to hybrids exhibiting courtship motor sequences not evident in any known species of duck or sometimes to hybrids possessing behavior patterns absent in both parent species but present in some presumed ancestral type (Wall 1963). However, it is still not clear what changes in the complex physiological basis of such behavior patterns are responsible for these differences. Dilger investigated the carrying of nest material in F₁ hybrids of Agapornis roseicollis parr at (male) x A. per sonata fischeri (female). Both parent species cut strips of paper or leaves and carry them to the nest. Females of the first species carry the strips in their bills, while females of the second species tuck the strips under special feathers on the lower back. The hybrids attempted to perform this latter pattern but failed for various reasons. For example, some were unable to let go of the strip of paper and tried to carry the strips in the bill and under the feathers at the same time. Within two years the behavior of the hybrids improved through learning, but they continued to perform ineffective tucking movements (Dilger 1962).

The genetic fixity of elements of behavior and the fact that they are nearly always to be found in more than one species prove their taxonomic value. In fact they are often characteristic of genera, families, or even higher taxonomic categories. For this reason it is possible to employ behavior patterns in the investigation of the relationships between animals. Indeed, Whitman (1898) and Heinroth (1911) investigated the behavior of doves and ducks respectively in the hope of finding characteristics useful for a more systematic analysis of their interrelatedness. In some grasshopper and toad species, species-specific calls or songs are used for species recognition; thus they represent barriers to interspecific reproduction. On the other hand, it is possible to reconstruct the phylogeny of behavior patterns on the basis of variations in the form of the same basic pattern between closely related species, as was pointed out by Darwin in The Expression of the Emotions in Man and Animals (1872). Exactly the same method is used in comparative anatomy and morphology. Although no behavioral fossils exist, more transitional forms exist between different behavioral types than is the case with morphological characteristics; behavioral characteristics occur repeatedly and at different intensities, while a leg is formed only once. The individual elements of various behavior patterns are, however, more open to formation of novel combinations (e.g., in contrast to the bones of the skull in vertebrates). For this reason, the phylogeny of behavior patterns must be based on the simplest possible elements.

We know that no behavioral characteristic is dependent upon only one gene, that each hereditary component affects several characteristics, and that there are not two separate sets of hereditary material governing body construction and behavioral features. The interaction of a behavior pattern with its effector organ is thus just as labile as the coadaptation of several functionally correlated organs.

Evolution and selection. Reimarus pointed out that in many instances behavior patterns adapted to the use of certain organs are performed, at times, even before these organs are developed. Apart from differences in speed of development of behavior patterns and their effector organs, it is also possible that one survives when the other is lost; a cerambycid beetle will continue to preen its antennas after they have been removed by dissection, mutant fruit flies (Drosophila) with no wings still perform the wing-preening movements typical of the species, stump-tailed monkeys, when they run along a branch, still show the balancing movements once effective in their long-tailed ancestors.

Such historical carry-overs can also be observed in behavior patterns originally adapted to certain environmental conditions which have since changed. Ground-breeding birds regularly use the beak to perform specific behavior patterns for rolling the eggs back into the nest if they are found outside. Tree-breeding birds do not show this, since the eggs that fall disappear. However, Poulsen (1953) was able to show that some birds which have recently evolved from ground-living stock to a tree-living habit still exhibit egg-rolling patterns, while some recently evolved ground-breeding birds lack this pattern. There are other examples which show that fixed action patterns can be extremely conservative in the evolution of a species. On the other hand, closely related species occupying the same area exhibit rapid phylogenetic changes in the sexual behavior patterns serving for sexual recognition. In fact, in some such species greater differences in species recognition signals are seen where two species occur together than where either species occurs in isolation. This phenomenon has been called character displacement.

Intraspecific signals usually undergo selection for better recognition (to avoid “misunderstandings”) and tend to become more and more conspicuous and outlandish. The behaviors involved are performed more conspicuously and are emphasized by morphological characteristics of color, form, or odor. In addition such behaviors are often rhythmically repeated. This fixed patterning often ceases to show different degrees of intensity. The level of motivation is no longer expressed in the intensity of the behavior but in how often it is repeated at one and the same fixed intensity (Morris 1957), much as the urgency of a telephone call is indicated by how often the bell rings and not how loud it rings. Finally such a recently formed fixed action pattern may become motivationally autonomous of the situation in which it was originally aroused by a process that Tinbergen has called emancipation. These and other changes in signal behavior patterns, leading to improved communication between signal sender and signal receiver, are referred to as ritualization. We still know very little regarding the physiological and neuroanatomical basis of both nonritualized and ritualized behavior patterns. [see COMMUNICATION, ANIMAL.]

It is commonplace to say that no animal performs the behavior patterns in its repertoire in random order. An animal responds to signals according to set principles. It is the task of the behavioral physiologist to analyze this phenomenon. This task involves large-scale studies of sensory physiology, since the animal receives the stimuli with its sense organs; of hormone physiology, since hormones can decide whether the sight of the female elicits courtship by the male, and so on; and of the physiology of the central nervous system, which is responsible for the analysis of the stimuli and for the coordination of the requisite behavior patterns.

Releasing mechanisms. The carnivorous water beetle Dysticus marginalis does not react to the sight of prey (e.g., a tadpole in a glass tube), although it has perfectly developed eyes, but it does react to the chemical stimuli emanating from the prey. If some prey-extract solution is added to the water, the beetle will clasp even inanimate objects immersed in the water. A male robin will attack a bundle of red feathers but not a perfect dummy of a male lacking the characteristic red breast. Such examples show that animals respond with quite specific reactions to quite specific stimuli among the many perceived from the environment. These relevant stimuli are called sign stimuli, or releasers.

Sign stimuli act upon specific functional units of the central nervous system, the so-called releasing mechanisms. The specific properties of these units may likewise be either genetically determined, in which case they are termed innate releasing mechanisms (IRM), or partially determined by learning. The releasing mechanism filters out the sign stimuli and thereby triggers off specific behavior patterns. Some behavior patterns can be elicited by more than one stimulus (e.g., an odor or a vibration). The vigor of the reaction generally depends upon the strength of the stimulus, and heterogeneous stimuli may summate (the same intensity of a reaction may be shown toward a strong odor or a strong vibration or a weak odor together with a weak vibration). Sometimes it is possible to present the animal with an abnormally strong stimulus and obtain a response stronger than that released by the naturally occurring stimulus; Magnus (1958) has shown that the males of the silver-washed fritillary butterfly react with courtship toward the orange and black color pattern of the female’s fluttering wings. By placing orange and dark stripes on a cylinder and rotating it, he proved that more rapid color-dark alternation than the rate characteristic of the female was more effective in eliciting the male’s reaction. The greater the speed of rotation of the cylinder, the greater were the courtship responses, right up to the physiologically demonstrated flickerfusion frequency for the species concerned. [see SEXUAL BEHAVIOR, article on ANIMAL SEXUAL BEHAVIOR.] This susceptibility of animals to supernormal releasers provides us with an insight into the reason for the development of bizarre morphological signal structures such as the feathers of the peacock. Some parasitic birds even capitalize on this phenomenon when their young are larger and more babyish than, and therefore preferred to, the host’s own young.

Motivation and drives. It has been observed that one individual will sometimes respond to a weak stimulus with a strong response, while at other times respond only at the same intensity or not at all to a much stronger releasing stimulus. It is therefore necessary to measure independently the specific “readiness” of the animal to react, apart from the strength of the stimulus. The strength of a reaction often decreases sharply with repeated equivalent stimulation, as is the case with escape attempts in aquarium fish in response to tapping on the glass pane or with gaping in young birds when the nest is lightly shaken. The readiness of an animal to perform certain patterns exhibits extensive and independent variation; an animal which is not prepared to eat may nevertheless exhibit readiness to flee. The readiness to perform a certain pattern is referred to as the motivation. Motivation (e.g., in hunger) often increases with the time interval from the last elicita-tion of the type of behavior concerned (“damming effect,” an effect which is related to the corresponding stimulus threshold). In the extreme case the action pattern can occur without any evident external elicitation–as vacuum activity. However, an animal with high motivation to perform specific behavior patterns (where the “drive” is under restraint) usually performs certain behavior patterns suitable for attainment of a stimulus situation appropriate to the motivated patterns. In simple terms, the animal “searches.” Craig (1918) observed the occurrence of restlessness, varied movements, and searching behavior as symptoms of a physiological state of appetite for specific stimuli and labeled such behavior appetitive behavior, as distinct from consummatory behavior, which lowers the degree of motivation when performed and leads to a state of satisfaction. It is important to note that the animal does not attempt to achieve the biological effect associated with the consummatory act but merely the performance of the consummatory behavior itself. The state of satisfaction can also be achieved by abreaction in response to models. In the simplest case, appetitive behavior consists of undirected locomotion, but many animals (especially higher-developed forms) learn from experience and modify the appetitive behavior, so that it more rapidly leads to success. They learn when, where, and how they can attain the releasing situation. Briefly, appetitive behavior is typically variable (plastic), whereas the consummatory act is relatively fixed (stereotyped). Motivational analysis attempts to demonstrate how many behavior patterns are dependent upon the same motivational source and how many partially or completely independent motivational centers are present in a given animal species. It is taken as axiomatic that there are fewer independent sources of motivation than observably distinct behavior patterns and that behavior patterns which regularly occur within short intervals from one another are thus commonly motivated–the motivational state of the animal oscillates more slowly than the alternation of behavior patterns. Further, it is known that behavior patterns exist which are characteristic for specific conflict situations; in the conflict between attack and flight these are represented by threat behavior. Such patterns are certainly motivated from different sources, which may vary independently from one another. It is not known from the outset how many of the behavior patterns observed have mixed motivation, but for the purposes of analysis it is assumed that it is the minimum possible. Wiepkema, a Dutch ethologist, carried out the following model experiment (1961) with the European bitterling: First he recorded the occurrence of the behavior patterns which he had identified for this species (ramming the flank of a conspecific with the head, scouring of the substrate, tail-beating, swimming before the female, etc.) over a long period of time. In this process typical locomotory sequences are found to occur regularly, while some behavior patterns are seen to be mutually exclusive within a given time interval. Wiepkema computed the minimum number of independent variables (i.e., motives) necessary to account for the observed distribution of action patterns. Mixed motivation was taken into account, but it was assumed that one given motive was predominant in each case. For the reproductive period of the bitterling it was found that three independent motivational sources are necessary and that each source governs a group of motor patterns which are totally or predominantly dependent upon the source concerned. These groups are comprised of (1) behavior patterns directed at the rival, objectively termed “fight,” (2) behavior patterns directed away from the rival, termed “flight,” and (3) the patterns carried out in combination with the female in association with spawning. Accordingly it is possible to refer to the predominant motivation in each case as (1) fight drive, (2) flight drive, and (3) sex drive. Some behavior patterns lie between these groups, however, and are thus more or less equally dependent upon more than one motive. For example, spreading of the fins combined with an undulating movement of the entire body, which we refer to as “threat,” is motivated by both fight and flight drives; a specific courtship pattern is motivated by both fight and sex drives. Using factor analysis it is even possible to rank the action patterns according to a scale of ratios between different drives. [see DRIVES; MOTIVATION.]

Various phenomena occur in conflict situations; the animal may combine two behavior patterns (e.g., warding off a rival and eating), it may oscillate between the intention movements of different action patterns (e.g., oscillation between motions toward attack and flight without actually attacking or fleeing), it may exhibit abreaction of an inhibited behavior pattern by transferring the direction to a neutral object (e.g., gulls which do not dare to attack a stronger rival may tear and pluck at tufts of grass), or it may exhibit a behavior pattern which does not belong to either of the motivational sources directly involved in the conflict. This last pattern is referred to as displacement activity. For example, domestic cocks will start to eat when they are involved in a conflict between attack and flight, while avocets will assume a sleeping posture. The physiological foundations of displacement activities have been investigated only in a few cases and appear to vary from case to case. Some behavior patterns may be dependent upon the same releasing stimuli as well as upon the same motivational sources. [see CONFLICT, article on PSYCHOLOGICAL ASPECTS.]

Sequential and hierarchical organization. The fact that some elements of behavior can give rise to conflict at corresponding integrational levels, while others are mutually exclusive, indicates that groups of elements are governed by superior systems which can similarly show mutual interference, promotion, inhibition, or exclusion. In this way, we arrive at the concept of a hierarchical system of dominant and subordinate drives. The same concept emerges from the comparison of releasing situations and appetitive behavior.

A hungry squirrel (1) climbs (2) trees (3) looking for cones; when motivated to build a nest, it (1) climbs (2) trees (3) looking for twigs. Thus different motivations may employ the same “lower” motor and orientation components. The latter are called taxes, a taxis being defined as orientation of the whole body or parts of it with respect to the source of stimulation. Further, the distinction between appetitive behavior and consummatory behavior is a relative one. Normally, certain appetitive behavior leads to a stimulus situation which initiates another, more specific, appetitive behavior. This fact has been carefully worked out by Baerends (1941) and Tinbergen (1951). The three-spined stickleback is brought into reproductive motivation by the gradual increase in day length in spring and begins migration inland into shallow fresh-water habitats. This factor, together with the rise in water temperature and the visual stimulation of heavily vegetated sites, is a releasing mechanism for the establishment of a suitable territory by the males. A territory is necessary for the male to acquire its characteristic red belly. Only then does it begin to react to particular stimuli which previously had no effect. The male will build a nest with suitable material, fight against rival males (where the releasing stimulus is the red belly of the male intruding into his territory), and court passing females, which present their silvery, swollen, egg-filled bellies to the male in a characteristic manner. Thus, the stimuli emanating from a territory will activate the fighting, building, and mating drives, which must then be elicited by special releasers. Fighting itself consists of a number of behavior patterns (chasing, threatening, tail-beating, biting), each dependent upon still further, highly specific stimuli emanating from the intruder’s behavior. The behavioral sequences of male and female form an alternating chain of reactions, each action of one partner releasing the following appropriate reaction of the other partner until the female spawns and the male fertilizes the eggs. The act of fertilization initiates brood care in the male; he now fans fresh water onto the eggs and continues to drive off rivals but does not exhibit further courtship until the young hatch. It is thus clear that there are chains of behavioral tendencies connected at higher and lower levels of integration and that these different levels are organized into a hierarchical system. The advantage of a hierarchy, as opposed to a stereotyped series of single fixed actions, lies in its adaptability to unpredictable sequences of events.

Neurophysiological aspects. It seems evident that some structural organization must exist within the central nervous system, paralleling the observed organization of behavioral responses–in particular the hierarchical organization. Neurophysiological investigation of fixed action patterns has therefore become an important branch of ethological research. Extending the earlier experiments of W. R. Hess (1949), Hoist and Saint Paul (1959) demonstrated the existence of structural hierarchical organization of the mechanisms underlying behavior by electrically stimulating specific areas of the brain in chickens. Well-coordinated, complete sequences of movements identical with those observed in normal behavior were elicited. All these sequences of behavior were composed of single actions, each of which could be obtained in isolation by stimulation of specific brain areas. Holst and Saint Paul combined brain stimulation with the normal releasing stimuli, electrically changed the “mood” (motivational state) of the animal and studied artificial conflict between drives by producing interaction of different behavior patterns with simultaneous elicitation.

Neurological research has substantiated the conclusion, derived from ethological field studies, that the coordination of many locomotive patterns arises from impulses generated in the central nervous system. Potent support has also been provided for Lorenz’ hypothesis postulating constant production of action-specific potentials in the central nervous system.

Habituation and imprinting. Most of the original schemata postulated for the functional structure of behavior have been shown to be simplifications, though correctly describing special cases. In order to arrive at a generalized schema, it is still necessary to modify repeatedly such hypothetical schemata. Even the hierarchical system must be altered to a multidimensional network. The concept of habituation likewise increases in complexity with time. A behavior pattern repeatedly elicited by a particular sign-stimulus will cease to occur after a given time. The sense organ can nevertheless be demonstrated to be fully capable of functioning, and it is not even necessary to presume that the motivation of the animal to perform this pattern is entirely extinguished; it is often possible to elicit the same behavior pattern immediately afterward with another sign-stimulus. In such cases, it is necessary to assume that central cut-off systems are involved. Such systems are capable of very complex functions; mechanisms of this type in turkeys extinguish flight behavior in response to all relatively slow-flying objects which occur frequently, and the adult animal flees only in response to uncommon flying objects. In fact, the most infrequently occurring objects which (relative to their own size) are slow-flying are birds of prey. The adult turkey thus shows a well-adapted flight reaction in response to predatory birds–but also to advertising balloons. It is a question of definition whether or not one refers to this effect as learning; it takes place without marked exogenous reward or punishment. The same is true of imprinting, which was described by Spalding as early as 1873. In imprinting, a specific reaction of the animal (which need not be functional at the time of imprinting) becomes attached to an object which later functions as the releasing agent. This occurs within a limited sensitive period, usually at a young age. In contrast to learning by association, there is no reward (as in the previous example), and even punishing stimuli have a reinforcing effect. If ducks or doves are reared by other species they will later show a pairing preference toward a partner belonging to the foster species, even when a conspecific partner is available. [see IMPRINTING.] Phenomena similar to imprinting have been discovered in many fields. Some juvenile birds learn the song entirely from the “father” and will learn the song of a foster-father even in the midst of conspecifics. Since later offspring learn from these birds, the possibility of “speech dialects” arises. In different mammal species there have been cases of traditions which largely concern food preferences or forms of food acquisition, although traditions may also arise in the avoidance of enemies.

IRENÄUS EIBL-EIBESFELDT AND WOLFGANG WICKLER

[Directly related are the entriesPSYCHOLOGY, article onCOMPARATIVE PSYCHOLOGY; SOCIAL BEHAVIOR, ANIMAL. Other relevant material may be found inCOMMUNICATION, ANIMAL; DRIVES; EVOLUTION; GENETICS; IMPRINTING; INSTINCT; LEARNING; MOTIVATION.]

BIBLIOGRAPHY

ALTUM, BERNARD (1868) 1910 Der Vogel und sein Leben. 9th ed. Munster (Germany): Schöningh.

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CRAIG, WALLACE 1918 Appetites and Aversions as Constituents of Instincts. Biological Bulletin 34:91–107.

DARWIN, CHARLES (1872) 1965 The Expression of the Emotions in Man and Animals. Edited by Francis Darwin. Univ. of Chicago Press.

DILGER, WILLIAM C. 1962 The Behavior of the Lovebirds. Scientific American 206, no. 1:88–98.

EIBL-EIBESFELDT, IRENÄUS 1966 Ethologie: Die Biologie des Verhaltens. Volume 5, pages 341–549 in Handbuch der Biologie. Edited by Ludwig von Bertalanffy. Potsdam (Germany): Akademische Verlagsgesellschaft Athenaion.

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LORENZ, KONRAD Z. 1965 Evolution and Modification of Behavior. Univ. of Chicago Press.

MAGNUS, DIETRICH 1958 Experimentelle Untersuchungen zur Bionomie und Ethologie des Kaisermantels Argynnis paphia (lep. Nymph). Zeitschrift für Tierpsychologie 15:397–426.

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SPALDING, DOUGLAS A. (1873) 1954 Instinct, With Original Observations on Young Animals. British Journal of Animal Behaviour 2:2–11.

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WIEPKEMA, P. R. 1961 An Ethological Analysis of the Reproductive Behaviour of the Bitterling (Rhodeus amarus Bloch). Archives neerlandaises de zoologie 14:103–199.

ETHOLOGY

Ethology is the biological study of animal behavior. It derives from the Greek root ethos, which, in normal English usage, refers to the manner of living, or customary behavior, of a social entity. One may therefore speak of the ethos of a particular sports club, small town, or professional organization, for example. By the same token, ethologists are concerned with the ethos of animals: their way of behaving.

Ethology traces its history to the early decades of the twentieth century, especially the work of the Austrian physician Konrad Lorenz (1903–1989), Dutch biologist Niko Tinbergen (1907–1988), and German entomologist Karl von Frisch (1886–1982); in recognition of their achievements, these three shared the Nobel Prize in physiology or medicine in 1973. The characteristics of ethology as a scientific discipline can be appreciated by comparing it to one of its well-known counterparts, comparative psychology.

Whereas comparative psychology is primarily concerned with understanding human behavior, such that animal research is conducted with an eye to better understanding Homo sapiens, ethology focuses specifically on the behavior of animals for its own sake. Similarly, comparative psychologists study a small range of animal species—particularly laboratory rats, macaque monkeys, and pigeons—as easily manipulated substitutes for human beings. By contrast, ethologists study the diversity of animal species, especially invertebrates, fish, and birds. Because of their underlying concern with understanding human behavior, researchers in comparative psychology are especially interested in examining the various concomitants of learning (which have a notable impact on human beings). Ethologists pay considerable attention to behavior that is loosely described as "instinctual," which tends to be more prevalent in the species with simpler nervous systems that are typically the subject of ethological research. Ethologists also emphasize the study of animal behavior in its natural context; that is to say, under field conditions where the organisms normally live and to which they are adapted by natural selection. By contrast, comparative psychologists typically conduct their research in a laboratory setting within which they can carefully control for extraneous factors while focusing on the role of various aspects of experience.

Some Aspects of Classical Ethology

Ethology, as the study of how organisms conduct their lives, long has been especially concerned with compiling careful, detailed descriptions of actual behavior patterns, known as ethograms. These detailed records (including verbal descriptions, photographs, and sonograms of vocal communications, for example) are not generally considered ends in themselves, but are fundamental to a rounded, ethological understanding of any species: Ethologists emphasize that they must first know what the animals in question do before they can pose meaningful questions.

According to Niko Tinbergen, those questions are especially concerned with the following:

1. How does the behavior in question influence the survival and success of the animal? In modern evolutionary terms, what is its adaptive significance; or, how does it contribute to the inclusive fitness of the individual and the genes responsible, recognizing that inclusive fitness involves not only personal, Darwinian reproductive success but also the effect of each behavior on the fitness of other genetic relatives.
2. What actually makes the behavior occur at any given moment? This might include the role of hormones, brain mechanisms, prior learning, and so forth.
3. How does the behavior in question develop as the individual grows and matures? What is its developmental trajectory, or ontogeny?
4. How has the behavior evolved during the course of the species' evolutionary history? In short, what is its phylogeny?

It is worth noting that of these, question a has become the special province of sociobiology, a research discipline closely allied to ethology and that emphasizes matters of adaptive significance and evolutionary—often called ultimate—causation. By contrast, question b is associated in the public mind with research into animal behavior more generally; it is often called proximate causation. Ideally, a complete understanding of animal behavior will involve both ultimate and proximate considerations, as well as attention to matters of ontogeny and phylogeny.

Through their research, early ethologists developed a number of concepts now considered part of "classical ethology." These include, but are not limited to, the following. Fixed action patterns are the fundamental building blocks of behavior, consisting of simple, relatively unvarying movements that are more or less independent of prior experience. Once initiated, fixed action patterns generally continue to completion even if the initiating stimulus is no longer present; this emphasizes the unthinking nature of these acts, which are the products of natural selection rather than complex cognition or daily experience. Fixed action patterns, in turn, are evoked by releasers, features of the environment or other animals to which the receiving animal is delicately attuned. The situation is analogous to a lock-and-key mechanism: a lock is carefully adjusted (in the case of animal behavior, by natural selection rather than by a locksmith) to the specific characteristics of a key. In ethological terminology, the lock is an innate releasing mechanism, a characteristic of the receiving animal—usually but not necessarily located in the animal's central nervous system—that responds to the traits of the releaser. Continuing the analogy, when the key fits the lock, a door opens; this is equivalent to the fixed action pattern. And, just as a door moves along a fixed, predetermined pathway, so do the behavior patterns with which ethologists have traditionally been most concerned.

Although it may appear that this schema is only capable of generating simple behaviors (a simple releaser evokes a comparably simple fixed action pattern), ethologists demonstrated that these connections can be "chained," such that fixed action patterns by one individual, for example, can serve as a releaser for another, whose fixed action pattern, in turn, serves as a releaser for another fixed action pattern in the first; and so on. In the process, complex sequences of courtship, parental care, or communication can be constructed.

In the courtship behavior of the three-spined stickleback fish—a species that has been intensively studied by ethologists—males develop a bright red abdomen in response to the warming water and increased day length of spring; females react to this releaser by their own fixed action pattern, a "head-up" display which in turn reveals their abdomens, swollen with eggs; the male, in turn, responds by his own fixed action pattern, a "zigzag dance," which involves swimming rapidly toward a nest made of algae that he would have previously constructed and then swimming quickly toward the female; the female responds by following the male; the male lays on his side in a characteristic posture "showing" the nest entrance to the female; she enters; he rhythmically prods the base of her tail with his snout, whereupon she deposits her eggs; she swims away; he enters the nest, fertilizes the eggs, and continues to care for them until they hatch. Throughout this complex sequence, each situation or behavior by one animal serves as a releaser for a fixed action pattern by the other, and so on in turn.

Ethologists also developed descriptive models for the control of behavior. Two notable models are the hydraulic model of Lorenz and Tinbergen's hierarchical schema. Lorenz proposed that a kind of motivational pressure—which he labeled action specific energy—builds up within the central nervous system of an individual. This energy is dissipated when the appropriate fixed action pattern is performed. In some cases, if the behavior in question is blocked, the motivational energy spills over into another channel, generating a seemingly irrelevant behavior, known as a displacement activity. For example, shorebirds known as avocets, when engaged in a dispute at a territorial boundary, may tuck their heads into their wing feathers, in a posture indistinguishable from that normally assumed during sleep.

Lorenz's scheme is also consistent with vacuum activities, whereby an animal may suddenly perform a fixed action pattern in the absence of any suitable releasing stimulus; in this case, presumably the energy associated with a given fixed action pattern has built up to such a level that it essentially overflows its neuronal banks and the relevant brain centers discharge in an apparent vacuum. Although the hydraulic model does not have many current devotees, it still serves as a useful heuristic model.

Tinbergen proposed a similar perspective, one somewhat more consistent with known neurobiological mechanisms. He suggested that various major instinctive tendencies (e.g., reproduction, migration, food-getting) were organized hierarchically, such that reproduction, for instance, was subdivided into fighting, nest-building, mating, and care of offspring, each of which, in turn, was further subdivided. Thus, depending on the species, fighting might involve chasing, biting, and threatening, whereas care of offspring might involve provisioning the young, feeding them, defending them from predators, and providing various kinds of learning opportunities.

Ethology in the Twenty-first Century

Despite the ethological focus on animal behavior that can loosely be labeled "instinctive," an important realization characterizes all studies of behavior, whether conducted by ethologists, sociobiologists, or comparative psychologists: Behavior always derives from the interaction of genetic and experiential factors. Variously labeled instinct/learning, genes/experience, or nature/nurture, contemporary researchers widely acknowledge that these dichotomies are misleading. Just as it is impossible for an organism to exist or behave without some influence from its environment (the extreme case of "pure instinct"), it is impossible for environmental factors acting alone to produce behavior (the extreme case of "pure learning"). Every situation must involve both factors: there must always be an organism to do the behaving, and, moreover, organisms with different experiences exposed to the same situations always respond somewhat differently.

Ethologists have branched out substantially from their earlier focus on careful naturalistic descriptions of animal behavior, increasingly blurring the distinction between ethology and various related disciplines. Thus, neuroethologists concern themselves with the brain regions and precise neuronal mechanisms that govern, for example, animal communication as well as the reception of auditory, olfactory, visual, and even tactile signals. Behavior genetics incorporates an amalgam of ethology and precise genetic techniques to unravel the genetic influence on various behavior patterns; such research may range from the creation of cross-species hybrids to the detailed analysis of DNA sequences in identified genes responsible for specific behavioral tendencies. Behavioral endocrinology investigates the role of hormones in predisposing animals toward courtship, aggressive, migratory, and other behaviors, as well as the environmental and social situations responsible for releasing the relevant hormones. Mathematically inclined ethologists have been increasingly interested in applying concepts derived from game theory in seeking to understand how behavior has evolved, especially in situations such that the benefit to each individual depends not only on what he or she does, but also on the behavior of another individual.

Ethology and Ethics

Researchers increasingly have been applying the basic ethological techniques of detailed, objective, nonjudgmental observation to human behavior as well. Human ethology is essentially an organized form of "people watching," whereas human sociobiology (sometimes called evolutionary psychology) seeks to apply the principles of evolution by natural selection to Homo sapiens. Critics assert that the former approach consists of a kind of empty empiricism, lacking powerful theoretical roots; others attack the latter for being overly driven by theory, occasionally lacking in adequate empirical findings.

The conduct of ethology occasionally raises ethical issues concerning the treatment of animal subjects, but generally such matters are more controversial in the laboratory-oriented disciplines such as comparative psychology and neuroethology. Because ethologists study undisturbed, natural populations, or—when conducting laboratory research—strive to maintain their subjects under naturalistic conditions, the major ethical dilemma facing ethologists tends to center around whether or not to intervene in the events of the normal lives of their study animals. For example, is it appropriate to prevent a forthcoming act of predation? (Ethologists nearly always answer in the negative, because they are typically committed to nonintervention on the lives of their subjects.) Moreover, because the goal of ethological research—unlike that of comparative psychology—is to understand behavior rather than to control it, and because—unlike evolutionary psychology—ethologists generally do not directly employ controversial assumptions about evolutionary factors currently operating on human behavior, ethology is generally free of the moral conundrums often attending its sister disciplines.

DAVID P. BARASH

SEE ALSO Aggression;Animal Tools;Dominance;Nature versus Nurture;Selfish Genes;Sociobiology.

BIBLIOGRAPHY

Alcock, John. (2001). Animal Behavior: An Evolutionary Approach. Sunderland, MA: Sinauer. The standard college textbook of animal behavior, which includes a good, if brief, treatment of ethology.

Barash, David P. (1982). Sociobiology and Behavior. New York: Elsevier. A wide-ranging introduction to sociobiology, emphasizing its distinction from classical ethology.

Goodenough, Judith; Betty McGuire; and Robert A. Wallace. (1993). Perspectives on Animal Behavior. New York: Wiley. A solid introduction to animal behavior that seeks to introduce both ethological and sociobiological approaches.

Gould, James L. (1982). Ethology: The Mechanisms and Evolution of Behavior. New York: Norton. A technical but rewarding early account of animal behavior, especially strong on physiological mechanisms.

Lorenz, Konrad Z. (1982). The Foundations of Ethology. New York: Simon and Schuster. Technical articles by one of the founders of ethology.

Tinbergen, Niko. (1989). The Study of Instinct. Oxford, UK: Clarendon Press. An early and now-classic account of ethology as a scientific discipline distinct from comparative psychology.

Ethology

The study of animal behavior as observed in the natural environment and in the context of evolutionary adaptation.

The pioneering work of Konrad Lorenz and Niko Tinbergen in the 1930s established a theoretical foundation for ethology, which has had an effect on such wide-ranging disciplines as genetics, anthropology, and political science in addition to psychology. Ethologists believe that an animal must be studied on its own terms rather than primarily in relation to human beings, with a focus on its normal behavior and environment . They study animal behavior from the dual perspective of both "proximate explanations" (which concern the individual lifetime of an animal) and "ultimate explanations" (which concern an animal's phylogenetic past). Proximate explanations answer questions about how a specific behavior occurs; ultimate explanations answer questions about why a behavior occurs.

Much of the field work performed by ethologists is based on the notion that an animal's behavior is generally adapted to its environment in much the same way as its physical characteristics. From the ethologist's point of view, a laboratory environment constrains animal behavior too much to provide a true understanding of its full range of functions and activities. However, the field work of ethologists consists of more than mere passive observation of animals in their natural habitats. In order to make observations about the behavior of an animal in its environment, ethologists often modify that environment. In a now-classic experiment, Lorenz managed to substitute himself for a mother goose, whose goslings then proceeded to follow him in single file wherever he went. In another well-known experiment, Tinbergen conducted a study of ground-nesting black-headed gulls to explain why a mother gull removes all traces of eggshell from its nest after a chick hatches. He hypothesized that the eggshell might be removed to prevent injuries, disease, or the attention of predatory birds. By placing pieces of shell in exposed locations away from the gulls' nests, Tinbergen found that the white interior of the shells were visible from the air and did indeed attract predators.

The ethologist's method of studying an animal begins with the creation of an ethogram, an objective description of its behavior patterns, including hunting, eating, sleeping, fighting, and nest-building. Four types of questions are raised about each activity: the cause of the behavior, development (within the lifetime of the individual animal), evolution (within the lifetime of the species), and adaptive function (how it helps the animal's species survive). Then, the researcher may turn to existing data on related species in various habitats and/or conduct independent research with reference to the animal's natural environment. Experiments may be conducted within the environment itself, or by investigating the effects of removing the animal from that environment. Laboratory studies may also be done, but these will usually be in relation to some aspect of the animal's own habitat.

Early theories of ethology focused on instinctive behaviors called fixed action patterns (FAPs), unlearned actions activated by "innate releasing mechanisms" that were thought to occur in response to specific stimuli. For example, submissive behavior could be regarded as a stimulus triggering an end to aggression on the part of a dominant animal. More recently, the focus of ethological theory has shifted to include an increasing awareness of behaviors that cannot be attributed to innate genetic processes, and learning has come to play a greater role in explanations of animal behavior. One example is the changing attitude toward the key concept of imprinting , first used by Lorenz to describe a nonreversible behavioral response acquired early in life, normally released by a specific triggering stimulus or situation. The differences between imprinting and ordinary learning include the fact that imprinting can take place only during a limited "critical period," what is imprinted cannot be forgotten, and imprinting does not occur in response to a reward. Imprinting was initially regarded as totally innate, but subsequent research has found that conditioning plays a role in this process.

Initially, ethology encompassed broad areas of behavioral study. More recently it has emphasized detailed study of particular behaviors. An emerging subfield, molecular ethology, focuses on how behaviors are affected by a single gene. Additional subdisciplines derived from classical ethology include sociobiology , which also involves gene study, and behavioral ecology, which relates behavior to the ecological conditions in which it occurs.

See also Adaptation; Comparative psychology

Further Reading

Moynihan, Martin. The New World Primates: Adaptive Radiation and the Evolution of Social Behavior, Languages, and Intelligence. Princeton, NJ: Princeton University Press, 1976.

Ethology

The study of behavior is divided into two sub-categories: learned behavior and innate behavior. Ethology is the study of innate, or instinctive, behavior. Scientists in this field study the mechanisms underlying specific behavior, as well as their evolution. Ethologists were the first to systematically and scientifically measure the natural activities of animals.

Ethology had its origins in a middle ground between the behaviorists, who believed that all behavior must be learned, and the classicists, who held that all behavior was inborn. According to ethologists, animals are genetically predisposed to learn behaviors that benefit their species, but this natural behavior can be modified, within limits.

The field of ethology was pioneered by three prominent European scientists during the first half of the twentieth century: Konrad Lorenz, Nikolaas Tinbergen, and Karl von Frisch. Lorenz, an Austrian scientist and physician, is referred to as the founder of modern ethology. He discovered the process of imprinting, by which newly hatched ducklings and goslings follow the first animal they see and hear as if it was their mother. Lorenz also conceived of the fight or flight response, a theory that attributes an animal's reaction to conflict as a compromise between two inner drives: to attack or to flee. Nikolaas Tinbergen began by studying the homing behavior of wasps and later worked with Lorenz. Tinbergen applied ethological concepts to anthropology, the study of human interactions, by linking human instinct to rituals. Karl von Frisch studied the sensory systems of fish, discovering that fish are able to see many colors and have relatively sensitive hearing. Von Frisch also demonstrated that honeybees have a sophisticated ability to use the sun's position for orientation and to utilize different dances to indicate a target's direction and distance from the honeycomb. These three researchers won the Nobel Prize in Physiology or Medicine in 1973 for their combined contributions to the field of ethology.

Neuroethology, a discipline that originated in the 1960s, combines ethology with neurobiology. It draws connections between outwardly observable, innate behaviors and the activity of particular regions of the brain.

Rebecca M. Steinberg

Bibliography

Bateson, Paul Patrick Gordon, Peter H. Klopfer, and Nicholas S. Thompson, eds. Perspectives in Ethology. New York: Plenum Press, 1993.

Krebs, John R., and Nicholas B. Davies. An Introduction to Behavioural Ecology, 3rd ed. Oxford, U.K. and Cambridge, MA: Blackwell Scientific Publications, 1993.

Tinbergen, Nikolaas. Social Behaviour in Animals: With Special Reference to Vertebrates. London: Chapman and Hall, 1990.

ethology Pioneered by Konrad Lorenz and Nikolaas Tinbergen, ethology applies evolutionary theory to early animal and childhood human behaviour, in order to examine its instinctive and adaptive nature. Its roots go back to Charles Darwin's Origin of Species by Means of Natural Selection (1859). Lorenz is usually credited with its discovery in the early 1930s. He is best-known for his studies of ‘imprinting’ and the instinctive basis of animal and human behaviour. His work had more impact on psychologists (as in John Bowlby's research on attachment and loss) than on sociologists: the latter usually argue that studies of animal behaviour are of little relevance in understanding human society.

Ethology became immensely popular during the 1960s in popular books such as Desmond Morris's The Naked Ape (1967). In this and his subsequent work, Morris sought to demonstrate the similarity, and hence the evolutionary significance, of certain aspects of human and animal behaviour. Critics have pointed to the reductionist assumptions behind much of the popular ethology of the 1950s and 1960s, which is regarded as one of the precursors of sociobiology.