The behavior of an animal is what it does, how it cares for itself, and how it reacts to other organisms and the environment in which it lives. The variety and complexity of animal behavior has impressed naturalists for years. Early naturalists were prone to attributing to animals the emotions of humans. They often made anthropomorphic judgements and suggested that many of the behaviors were "instinctive" without defining that term.

The scientific study of animal behavior really began with Margaret Morse Nice who worked with some sparrows that nested in her garden as subjects. The science of ethology or animal behavior grew out of these early studies with an Austrian, Konrad Lorenz and Niko Tinbergen working in England being two early giants in the field. Ethology, the study of animal behavior, has as its basic premise: one must observe arrivals under natural conditions to understand their behavior. Psychology is the science of mental processes and behavior in humans. Psychologists study behavior in the lab. Ethologists stress the importance of observation or seeing what the animal does in its natural setting whereas psychologists stress the importance of tests and experiments with the animals under control and finally ethologists are more concerned with instinctive behavior; psychologists with the animals ability to learn.

When faced with a new behavior or series of behaviors, the ethologist asks a number of basic questions. These include:

Any behavior that an animal repeats in the same way is stereotyped; any behavior that is the same in all members of a species is species-specific. Any behavior that is performed without prior learning is called innate or instinctive. Each instinctive behavior has its own set of internal factors, hormonal and otherwise that, when they build to a certain level allow the behavior to take place. Then if given an external stimulus the animal acts. This buildup is called the specific action potential, meaning the power to perform a certain act. The specific action potential is responsible for an animal performing one behavior in preference to other behaviors. As the specific action potential builds the animal becomes restless and performs appetitive behavior, an introductory phase of the specific behavior pattern that "sets the stage" for the instinctive behavior. Predators may be roaming, following no particular path, when a prey animal bolts. The actions of the predator become instinctive, it pursues and kills the prey. The appetitive behavior is reduced when the prey is seen and ceases with it being eaten. Sometimes when the specific action potential is high and no external stimulus releases the accumulated specific action potential the animal may act without a stimulus, at least without any stimulus we are aware of. Such behaviors are termed vacuum activities. For example a bird that hunts, catches and eats insects may perform all the actions of hunting, catching and swallowing even though no insect or other visible stimulus is present. A behavior pattern or structure, which serves to trigger a behavior pattern, is called a releaser. There seems to be a specific release for each behavior pattern. It is almost like a key opening a lock. The sounds of young can serve as releasers as can color patterns. Sometimes a releaser functions but a learned response such as fear interferes with the normal behavior pattern. If two aggressive birds meet at the edge of a territory each may have a releaser to attack but the fear of the opponent stifles the attack response and an unusual behavior called displacement activity occurs. For example two herring gulls in a conflict situation instead of attacking may preen and a young child may chew fingernails. Occasionally one of two aggressive herring gulls instead of attacking one another or fleeing instead pull up clumps of grass, a type of behavior called redirected activity.