In order to survive, an animal must be able to respond to changing conditions in its environment. In other words, it must adapt. Animals’ responses include simple reflexes based on instinct and learning, as well as more complex patterned behavior, such as the division of labor among communities of some insects and the hierarchical system of dominance of such mammal groups as wolves. Mating and feeding are the most important activities, and behavior rituals related to these activities often develop.
Instinct and learning
All animals are born with a range of inborn behavior patterns. The knowledge of how to do certain things, called instinct, is passed from parent to offspring genetically. This form of inherited behavior helps an animal survive in its environment.
In addition to instinct, animals are able to learn ways of coping with their environment and can thus modify their behavior to deal with problems that they have encountered before. Some scientists who study animal behavior consider this ability to learn to be a measure of an animal’s intelligence.
Most animals use a combination of instinct and learning to adapt to their environment; the longer an animal’s life span and the more complex its life style, the larger role learning plays in its life. A large predatory mammal, for example, has a built-in hunting ability that is improved by learning. A fly, by comparison, which lives for only a short time, needs only to feed and breed successfully before it dies. It does not have the time to learn how to find a mate, or where it would be best to lay its eggs. Instinct provides the fly with a fixed set of adaptive responses so that it can cope even though it has no previous knowledge of a situation. Instinct is also important when there is no parental care, when the animal is not able to learn by example.
Instinctive reaction is characterized by two features: it is the same for all members of a species, and it can be initiated by a simple stimulus. But the division betweenThe role of sense organs instinct and learning is not immediately obvious. All animals of a particular species show the same reaction to a particular stimulus, even if they have been isolated from birth, although animals also often carry out learned activities in a similar stereotyped fashion, which may appear to be instinctive. Responses learned in isolation vary, however, among individuals of a species, depending on how they were taught.
An animal’s ability to learn and remember is, to a certain extent, dependent upon the life it leads. A worker bee, for example, must be able to learn the position of its hive and the location of flowers that are good for foraging, but a fly does not need this ability. It is not surprising then that experiments have proved that whereas bees can easily remember the position of plates of food, flies are less able to do so.
Insight is probably the highest form of learning—when the answer to a problem arrives in a sudden flash. The term is used to describe the rapid solution of a problem, skipping the process of trial and error. An example of this is the immediate construction by some chimpanzees of a “ladder” from objects in order to retrieve fruit that is too high to get at by stretching their arms.
Another type of learning is imprinting, which is thought to occur only over a short, critical period when the animal is very young, or at crucial times of an animal’s life, such as at the production of offspring. Imprinting occurs in both mammals and birds. Young songbirds, for example, are not able to sing an adult version of the species song if they have never heard it. They will sing, instead, a simple version of the song, without any characteristic trills. But a young bird that has heard the adult song only once will be able to sing it perfectly at a later stage because it has imprinted the song.
Small animals and birds also imprint any object that is near them soon after birth. This “maternal” imprinting ensures that the young follow the mother, as waterfowl do. But young birds can be caused to imprint balloons, puppets, cardboard boxes, and even human beings.
Apart from maternal imprinting, there is also sexual imprinting. An animal that has, for some reason, managed to imprint the wrong species, or an inanimate object, will not mate with its own kind. This imprinting was illustrated in an experiment in which a male zebra finch was raised by a pair of Bengalese finches. When the zebra finch reached maturity, it was placed in a cage with a female zebra finch and a female Bengalese finch; the male ignored the female of his own species and courted the Bengalese female, despite her lack of interest.
Scientists believe imprinting is largely based on smell and may account for a mother’s recognition of her offspring. For example, when cows and wildebeests give birth, the mother imprints the smell of her offspring and is then able to identify it in a herd.
The role of sense organs
In addition to instinct, learning is closely associated with responses that result when sense organs are stimulated. Most animals are aware of and respond to changes in light, gravity, temperature, and noise, but they do so in different ways.
Many animals forage for food, then bring it back to their home to eat. However, they need to orient themselves in their environment and recognize signs to find their way back. Digger wasps, for example, recognize the pattern of landmarks around their burrows. If the pattern were changed, they would not immediately recognize the position of their burrows.
Stimuli such as those used in courtship displays are often spread over a few hours or days and have a cumulative effect on an animal. These stimuli break down defensive barriers between the male and female and also bring the female into a sexually receptive state so that mating can take place. The breakdown of defensive behavior is necessary in certain species that instinctively attack or run from any other living thing. If a male scorpion or spider intending to mate does not approach the female cautiously, for example, she may attack or kill him.
Animals respond to stimuli that are quite different from those that humans can perceive. For instance, for many years zoologists wondered why some flowers that depended on bees for pollination were completely white and apparently had no guiding pattern (nectarguides) that would lead the insects to the nectar source. The scientists later discovered that bees can see ultraviolet light, and that some flowers have very distinctive ultraviolet patterns.
Color also plays a part in stimulating sexual behavior. For example, during the mating season, the belly of the male stickleback fish becomes red and his back turns blue-white. This coloration attracts females, which during the mating season are plump with eggs. The male guides a female to a nest that he has constructed. She enters it, and he nudges her from behind, causing her to release the eggs. She then swims away, and the male enters the nest and fertilizes the eggs.
Many visual stimuli to which animals respond are crude. For example, a robin will attack a clump of red feathers in its territory during the breeding season, and some cuckoos automatically feed a gaping mouth whether it is that of a fish or a baby bird. But sometimes animals respond to an artificial stimulus more vigorously than a natural stimulus. For example, if offered an egg considerably larger than their own, oyster catchers and other birds will try to hatch it instead of their own egg. Herring gull chicks peck at a red patch on the lower part of the parent’s yellow bill, which causes the parent to regurgitate food. But scientists have found that a red and white striped pencil causes the chicks to peck more vigorously than a real gull bill. This indicates that the chicks prefer to peck at a bill with a high level of contrast. This is a case of misfiring, when the animal’s behavior is stimulated under inappropriate circumstances and the animal’s needs are not met.
Scent organs are essential for most animals to locate scent trails to food sources, but scent is also important in communicating fertility. At the time of estrus, the period when a female is able to become pregnant, many female mammals secrete highly scented body chemicals called pheromones, which the males can detect. The phermones emitted by some insects can be detected at a distance of several miles.
Animals have many different ways of rearing young. In some ducks, for example, the male deserts the female to mate with others in that season. In sticklebacks and other types of fish, however, the female leaves after spawning, and the male protects the eggs and cares for the young until they become independent. But among many birds and some mammals both parents care for the young, which may be unable to feed themselves or maintain an adequate body temperature for several weeks after birth.
Ties between parents and their offspring are not necessarily exclusive. As many as a hundred pairs of sociable weavers raise their chicks together in a large nest, and many primate groups work together to protect the young from predators. Prairie dogs go a step further. A young prairie dog may be suckled by any lactating (milk-producing) female in the community and groomed by any male.
The life styles of all animals are organized chiefly around their method of obtaining food. Some parasites (animals that live in or on the bodies of other animals), for example, modify the behavior of their host to ensure that they will go on to the next stage of their life cycle. For example, some fish parasites cause their hosts to swim closer to the surface of the water than those free from parasites. This makes it more likely that the fish will be eaten by birds, which then become the hosts for the next stage of the parasites’ life cycle.
Many animals feed in groups. This behavior provides the animals security because it is more likely that a predator will be detected by one member of the group sooner than if the animals are feeding separately. In addition, animals grazing in a group look up less often than when they are on their own, which means that each individual can spend more time eating.
Some animals are solitary all the time, and others are solitary most of the time but come together for certain activities, such as migration. A species of locust has a solitary phase, when its coloring is green. But when environmental conditions are favorable, the insects change : olor to black and russet and become part of a migratory swarm. Some birds, such as the Eurasian robin, will attack any member of their own species that comes near their territory, but will join a flock that migrates as winter approaches.
Other animals gather and coordinate their activities. Termites, ants, and bees, for example, live in highly structured societies, or colonies. The division of labor between the different animals in the colony is strict, and the number of different kinds of individuals depends on what the colony requires for its survival. The colonies are controlled by pheromones that are produced by the queen. These chemicals and the high degree of physical contact between members of a hive ensure that the community works together effectively.
Most primates live in groups. These groups are less regimented than those of social insects, but order is maintained by a social hierarchy, which is headed by a single dominant male, usually the oldest and largest. This male has the first choice of the best food and most receptive females. Aggressive confrontations are usually avoided by the use of a large number of facial expressions and dominant or submissive gestures.
Animals that live in close communities often hunt together. Lions, for example, hunt by stalking and then ambushing their prey. But hunting dogs run down their prey in packs.
There is usually no dominant dog, male orfemale, although one dog will determine the direction of movement of the group. The dogs return to the lair after the kill, where the pups wait, and the whole pack feeds on regurgitated meat.
Animals such as hunting dogs, which have a high-protein diet, can afford to spend a lot of time in activities such as play because the energy value of the food they consume is high. Play involves romping and mock fighting and is important to young animals because through play they learn skills that they will need as adults.