The term animal behavior is used to collectively designate how an animal responds to the environment that surrounds it and to conditions within its body. Environment includes plants and other animals as well as such nonliving constituents as light and sound. Knowledge about animal behavior comes primarily from observations of the animal's activities both in controlled laboratory experiments and in the wild. The study of animal behavior is called ethology.
All kinds of behavior, both simple and complex, result when an animal responds to a stimulus. A stimulus is a change in some aspect of an animal's environment or a change that occurs inside the body. The behavior of an animal is limited by its physical structure, especially the level of development of its nervous system and sense organs. Each successful animal species has through time evolved the physical characters and the appropriate behavior to allow it to survive and reproduce.
Depending on what sense organs an animal has, it may react to temperature, light, sound, touch, taste, and smell. In addition, an animal responds to various stimuli from inside its body. Mating behavior, for example, depends almost entirely on the presence of various hormones in the body. Drives for food, water, and oxygen are triggered largely by events inside the body. (A satiated animal will seldom eat even the most tempting of foods placed before it.)
When behavior is neither learned nor modified by experience it is said to be instinctive. Instinctive behavior is said to be innate; that is, its pattern is inborn and determined by the animal's heredity. For example, a newly hatched pipefish instinctively knows how to hunt for food, and it will hunt as well as the adult members of its species.
A special type of innate response found in animals with a central nervous system is the reflex action. The knee-jerk reflex in humans is an example. A similar action occurs in frogs: if a frog's toe is pinched, the leg is lifted. This reaction occurs even if the frog's brain has been removed.
A reflex usually involves a single muscle or single set of muscles, but instinctive behavior involves the animal as a whole. Furthermore, a reflex will occur only as long as the stimulus is present, but instinctive actions continue even after the stimulus that started the activity has disappeared.
Many animals, from earthworms to apes, are capable of learned behavior; that is, they can alter their instinctive behavior by drawing on past experience. Learned behavior includes habituation—in which an animal learns not to respond to certain stimuli. A dog, for example, learns not to react to certain noises that its past experiences have shown to have no harmful effects. Most animal behavior is a combination of instinct tempered with learning.
Intelligent behavior, in which an animal behaves with insight and reason, is found in varying degrees in many animals. It is often difficult, however, to distinguish between learned behavior and intelligent behavior. There is evidence, however, that such animals as dogs, rats, bears, apes, and certain species of birds are capable of some intelligent actions.
Although relatively few species of animals display the complex social activities of social insects, very few animals are not at one time or another social. The interactions between parent and offspring are social activities; so are courtship and mating between the sexes. Social behavior, like other behavior, contributes to the success of the species, and it depends on communication.
Human beings are the only animals to possess language in the true sense of the word. Other animals communicate mainly through comparatively simple signals. Signaling behavior is largely instinctive, but responses to signals (though often instinctive) are in many animals improved by learning. Scent, vision, and hearing are all used for communication.
Communication between different kinds of animals is basically limited to a warning to stay out of private territory. Among their own kind, animals give signals to warn of impending danger, to protect their territory and young, to attract mates, and to tell the location of food sources.
To communicate with other geese, the graylag goose depends largely on changing its posture. Certain fish change not only the position of their fins but also their color to communicate fear, aggression, or readiness to spawn. Frogs, some reptiles, and almost all mammals and birds communicate to a large degree by sound. Dolphins and whales communicate through a wide variety of underwater sounds.
Bees can communicate to other bees the location of food by performing a specialized dance. Various animals give off a scent that can be readily identified by others. Such scents are used to set off territories, attract mates, and mark the way to food supply.