CHILDHOOD AND PLAY OF ANIMALS Real childhood and youth are found only in birds and mammals. It is the period of life in which young animals, while moving around and forming impressions more or less independently, still enjoy the protection of their parents. It is true that young mammals and birds are equipped from birth onwards with the necessary inborn reflexes and instincts to enable them to maintain their lives and to conform to the habits peculiar to their species. Nevertheless, in these animals, numerous faculties require prac tice. The young have to learn the use of their limbs by experi ence. At birth chicks and ducklings are endowed to different degrees. Both possess the inborn reaction of standing on one leg and scratching the head with the other. A chick succeeds from the very beginning, but a duckling loses its balance in its first efforts. It learns by experience how to balance its body while carrying out the movements. Through practice the co-ordination of the instinctive movements is improved. In the chick the instinct to drink and the co-ordination of the necessary movements is inborn. But to set the train of movements in action a releasing stimulus is necessary. Normally this is supplied by the sight of the hen drinking. But the mere sight of water, or the feeling of standing in water, in no wise acts as a stimulus. If, however, grains of corn are thrown into the water, the chick pecks at them at once, and the drinking reflex is immediately set in action by the wetting of the beak. Next time, the stimulus of water on the feet is sufficient. Sucking of the mother's milk by a young deer is an inborn instinct, just as is the action of following the parents through a wood. But the commencement of the act of sucking is a reflex depending on its own adequate stimulus, which is normally supplied by the mother's teats. A fawn in captivity will only suck at a feeding-bottle after the teat has been moistened with milk. The voice of many birds can be heard after they hatch out of the egg. But when, for instance, the mother bird makes it known by a warning call that a bird of prey is flying by, a young moorhen immediately ceases to hammer at its egg-shell and to tweet. It
keeps still until informed by a different call from the mother that the danger is past. This is a further example of the purposeful nature of instincts, although the animal has not the faintest con ception of the significance, object or result of its behaviour.
In species of animals where the struggle for existence makes particular demands on the abilities, parents usually "instruct their young." (See EDUCATION IN ANIMALS.) Normally there is again no question of any intentional, conscious, systematic in struction. Young birds are obliged to learn how to fly correctly. Under the protection of their parents, young storks and birds of prey copy their movements, and young swifts practice fly-catch ing. Young water-birds have of ten to learn to swim and to dive. Whereas young ducks go at once to water, young swans and gulls must be taken there by the mother. Male and female falcons together teach their young to hunt. They let captured prey drop down on to the young which have followed them up into the air.
Play (see also PLAY IN ANIMALS) affords a means of practising the use of the limbs, of gaining the skill requisite for independ ent life and of acquiring strength. Hence play is principally found in young animals, but it is seen too in the adult. This is particularly the case with predaceous animals, where it has the same significance as in young animals, being a sort of gymnastics or sport. This conception of play, first brought forward by Groos (1907), is now generally accepted. It has replaced the earlier opinion of Herbert Spencer that play is the expression of an over flow of energy. Types of play may be subdivided into movement, hunting and fighting games. The so-called "love-play" of adult animals is of quite a different nature. As an instinctive activity for the heightening of sexual excitement love-play is an aid to sexual reproduction.