ANIMAL BEHAVIOUR (Part 3 of 3)

The Prairie Dog Coterie - A Complex Social Group

The prairie dog is a rodent that maintains an elaborate social organization. Bond formation among prairie dogs depends on the exchange of auditory, visual, and chemical stimuli. The coterie the social unit of the prairie dog is maintained in a network of burrows occupying a fairly restricted area.

Prairie dog pups are altricial at birth that is, they are so undeveloped that they need adult aid for survival. When the pup is born, its mother is attracted to the helpless young organism. She licks the pup as it emerges from the birth canal, thus replenishing the salts she lost before and during birth. While licking the pup, she breaks the sac in which it developed as an embryo and thus stimulates its breathing response. The pup, still wet from birth, is attracted to the warmth of the mother's body. Moments after birth, the mother and her offspring are exchanging highly attractive stimuli, quickly forming a social bond.

As the pup nurses, it relieves the pressure in the mother's milk gland. Again, the exchange of stimulation strengthens the bond between the mother and her offspring, thus helping to ensure the infant's survival.

As the pup matures, other stimuli become attractive. When it is able to see and hear, the pup begins to recognize the relationship between stimuli that occur at the same time. Soon it leaves its burrow and encounters other adults that it stimulates. From birth, the prairie dog is constantly nuzzled and licked by its mother. When it emerges from its burrow, it is handled similarly by other prairie dogs.

Grazing land, non farm area where animals feed on grass or other plants.

These behavioural patterns maintain prairie dogs in a well-organized life space. There, the family unit reproduces, finds shelter, and feeds. Being grazers, prairie dogs check the growth of tall grasses that would prevent them from easily spotting predators. At the same time, their grazing habits encourage the dominance of fast-growing plants. Thus, the social organization of prairie dogs influences the ecological balances in their environment.

Limited grazing space soon forces maturing prairie dogs to seek new areas. When they enter the burrows of another coterie their odour marks them as strangers, and they are rejected. Pairs of rebuffed animals band together to form new coteries.

The Chimpanzee Family

The chimpanzee is one of the great apes. It lives in a family unit even more complex than that of the prairie dog. The chimpanzee family moves as a group through familiar feeding and resting areas. It has also evolved effective ways of defending itself against predators or from belligerent chimpanzees attempting to mate with the family's females.

When a chimpanzee has been attacked or has spotted a predator, it lets out an intense cry that raises the level of excitement of the other members of the family. They scream at the predator, throw rocks and other objects, and scamper off. As they flee, the females and the youngest chimpanzees are surrounded by the juveniles and the young males. The largest males guard the group. Thus, the action of a single chimpanzee serves as a signal that affects the behaviour of the rest of the family.

Animal Communication

Communication in the animal world takes many forms. These include chemical, visual, and audible signals. Attacked insects secrete a pheromone that so excites their con-specifics that they either attack or escape from the predator. Flocks of birds behave similarly, except that sounds rather than chemicals trigger the response. Vocalization also evokes social responses in the porpoise, an aquatic mammal. Porpoises communicate by means of whistles and other sounds. When a porpoise is born, females may be attracted by the mother's whistles. They swim to the baby and nuzzle it. The mother does not attack other females at this time. Possibly, this experience with many adult porpoises in the earliest days of infancy helps form the tight social bond of porpoises.

Reciprocal stimulation affects the behaviour of any animal, whether briefly or for a long time. Each organism is the source of environmental changes that affect other organisms. For example, after an amoeba ingests a food particle, it excretes a metabolic by-product that changes the chemical characteristics of the environment. If another amoeba is nearby, it tends to approach the first, though it will not do so if the chemical concentration is too intense. A sexually mature male cricket stridulates rubs its legs together and produces a sound whether or not another cricket stimulates it. However, it is more likely to stridulate when it hears another cricket.

When one animal can prompt an anticipated response in another, it displays a more advanced type of communication. For example, in an experiment a chimpanzee was trained to obtain a banana by pulling on a rope attached to a weight. Then the experimenter increased the weight so that one chimpanzee could not raise it but two could. If the second chimpanzee had already been trained to pull the rope, the first was able to stimulate it to do so by gesture, vocalization, and shoving. The two would then pull together and get the banana. In this case, the consequence of the second chimpanzee's behaviour was in some way anticipated by the first.

The directed activity of one animal toward another for the solution of a problem or the attainment of a planned goal is evident only in advanced species. Furthermore, man is the only species capable of transmitting ideas through a complex system of speech and writing.

The study of the evolution of language has given rise to a science called semiotics. This science attempts to understand the similarities and the differences among the many forms of communication.

Heredity and Behaviour

The evolutionary principle of selective adaptation holds that a species survives when it is able to adapt to environmental changes and when it is able to transmit to its offspring the genetic information that makes such adaptations possible. But how do genetic processes contribute to the development of behavioural patterns? Which behavioural patterns are hereditary? Which must be learned by each new generation?

In an effort to answer such questions, behavioural scientists have designed a number of experiments. In one type of experiment, closely related species with distinctly different behaviour patterns are hybridized. For example, two species of parakeets that practically share a natural habitat but do not interbreed were crossed in the laboratory. The parakeets of one species ordinarily tuck nesting material under their tail feathers. The others carry it in their beaks. The hybrid female offspring made inadequate tucking motions with the nesting material, and the twigs fell out from their feathers. However, all the hybrids carried the nesting material successfully in their beaks. Scientists felt that since all the hybrids performed some part of the tucking behaviour, it was probably the earlier form of behaviour in the evolution of these species.

The relationship between heredity and behaviour has fuelled an old but continuing controversy in the behavioural sciences. Some scientists believe that genetic processes underlie every kind of behaviour, while others think that the environment can modify genetically influenced behaviour In one type of experiment testing these views, animals with different genetic backgrounds are reared in the same environment. In another type, animals with the same genetic backgrounds are raised in different environments.

Chaffinch, European bird of the finch family, sought as a cage bird because of its beauty of voice and its ability in learning to sing tunes.

Cross-fostering is used to rear species with different genetic backgrounds in the same environment that is, the young of one species are raised by a female of another species. In one cross-fostering study, a female great tit reared a baby chaffinch with her own babies. Great tits and chaffinches are closely related birds that feed in different ways. The great tit holds food under its feet; the chaffinch does not. A chaffinch hatched by a great tit did not use its feet during feeding, while its nest mates did. Its feeding behaviour remained typical for its species, although it had no opportunity to observe other chaffinches.

However, when a great tit was reared in isolation, though it too demonstrated species-typical behaviour by holding its food down, it did so very clumsily. Only after repeated tries did its performance improve. This experiment showed that experience may be important even in genetically determined behavioural patterns.

Manipulation of the physical environment was used to study the subspecies of deer mice. One subspecies lives in the forest, is a climbing animal, and has a longer tail and larger ears than the other, a prairie subspecies that lives in grassy fields. The two subspecies were reared in the same laboratory and then released in a room containing artificial grass and wooden posts with flat tops. Although neither subspecies had experienced its species-typical environment, the forest deer mice organized their life space around the "trees," and the prairie deer mice settled under the "grass." However, when prairie deer mice were bred in a laboratory for more than a dozen generations, they no longer showed a preference for the field. The environment eventually so altered the genetic processes of these experimental animals as to change their species-typical behaviour.

Meadowlark, bird of the genus Sturnella, family Icteridae; sharp-billed, 8 to 11 in. (20 to 28 cm) long; two North American species streaked brown above, with yellow breast crossed by black V; western meadowlark (S. neglecta) known for intricate fluting call.

Bird-song patterns are species-specific and have, therefore, been regarded as genetically determined. Studies of the development of species-typical song patterns have helped to clarify the relative roles of heredity and experience in the development of such patterns. For example, if a meadowlark is exposed to another bird's song while it is learning to sing it will learn the other bird's song; however, if the meadowlark is exposed to the songs of other meadowlarks along with those of another species, it will learn only its own species-typical song. The bird instinctively chooses its species-typical song when it is in a situation in which there is a choice.

The response patterns of birds are so varied that the contributions made by genetic processes and by the auditory and other experiences of a bird during singing are hard to separate. It may be that in the course of its development a bird produces certain sounds that are a function of its peculiar body make-up These sounds may be the fundamental vocalization of the bird's species. Additional experience by the bird with hearing and producing its own song, as well as hearing those of other birds in a social setting, may yield the "dialect," or song pattern, associated with the species. However, genes do not carry this pattern as such. Rather, they carry the code for the biochemical processes that develop certain body systems that, aided by experience, will affect the animal's behaviour in its typical environment.

Assisted by Ethel Tobach, Curator, Department of Mammalogy, American Museum of Natural History, New York City.

BIBLIOGRAPHY FOR ANIMAL BEHAVIOUR

Black, Hallie. Animal Cooperation: A Look at Sociobiology (Morrow, 1981).

Caras, Roger. The Private Lives of Animals (McGraw, 1987).

Fraser, A.F. Farm Animal Behaviour, 2nd ed. (Saunders, 1983).

Freedman, Russell and Morriss, J.E. The Brains of Animals and Man (Holiday, 1972).

Lydecker, Beatrice. What the Animals Tell Me (Harper, 1982).

McFarland, David, ed. The Oxford Companion to Animal Behaviour (Oxford, 1981).

National Geographic Society. How Animals Behave (National Geographic, 1984).

Pringle, L.P. Animals at Play (Harcourt, 1985).

Pringle, L.P. The Secret World of Animals (National Geographic, 1986).

Waller, E.J. Why Animals Behave the Way They Do (Scribner, 1981).