Discovery Science: Ethology – Instinctive behavior

Earth Science: Ethology – Instinctive behavior

Instinctive actions, or fixed action patterns, are similar to reflexes, rigid and irreversible but with a greater range and complexity.

Examples are the nesting behavior of birds and the stockpiling behavior seen in hamsters.

In contrast to unconditioned reflexes the innate stimulus threshold, which triggers a stimulus of instinctive action, is variable. The process of a fixed action pattern can be divided into three phases. It begins with appetence behavior, that is the undirected search for a stimulus which may trigger an instinctive action (for example, undirected food searching during periods of starvation).

The second phase is called taxis or directed appetence which is a targeted approach to the source of a stimulus (for example, smelling food). The third phase is the genetically coordinated fixed action pattern. It is a species-specific activity that is irreversible once it has been triggered. Following the previous food-related examples, this would be the intake of food.

Conditions for a fixed action pattern are a willingness to act (motivation), a sign stimulus, and an innate trigger mechanism. All three factors depend on the same motivation to carry out an action that requires a stimulus, but they can be triggered by various stimuli. This includes intrinsic factors such as hunger or hormones, as well as outside factors such as day length.

Motivation decreases after successful completion of the fixed action pattern. A stimulus that triggers instinctive behavior is called a sign stimulus; if it comes from an individual of the same species, it is called a releaser. In experiments dummies are used to determine which stimuli act like sign stimuli. Often, several sign stimuli or certain combinations of stimuli are more likely to trigger a response than one stimulus by itself.

Dummies with artificially exaggerated sign stimuli may exceed the extent of the natural response (super-optimal sign stimulus). The nerve mechanism of the central nervous system that recognizes a sign stimulus and differentiates it from other stimuli is called the innate release mechanism. It triggers the appropriate behavior that corresponds to the sign stimulus.


Fixed action patterns often do not occur in isolation, but rather in the form of a series of individual actions where one follows the next.

A conspecific release of an instinctive action series by an animal is called an action chain. During the courtship display of stickle- backs, every action triggers the partner’s next action.


A DISPLACEMENT activity is the result of a conflict of instincts. The motivation to perform two. opposing actions is so equal that neither action is performed