in classical ethology, a hypothetical supply of motivational energy within an organism that is associated with specific unlearned behavioral responses known as fixed action patterns. Each response has its own energy supply, which builds up until the organism encounters the appropriate stimulus (see releaser) that triggers the response and thus depletes the energy supply. After the response and in the absence of the releaser, the action-specific energy begins to build up again. [proposed by Konrad Lorenz]