sign stimulus (releaser) The essential feature of a stimulus, which is necessary to elicit a response. For example, a red belly (characteristic of courting male sticklebacks) is the sign stimulus necessary to provoke an attack from a rival male; even a very crude model fish is attacked if it has a red undersurface. Similarly, territorial fighting in male robins is triggered by the sign stimulus of a red breast; a bunch of red feathers is enough to induce territorial behaviour. See also stimulus filtering.

sign stimulus (releaser) Part of a stimulus that is sufficient to evoke a behavioural response in an animal (e.g. the patch of red colour that provokes an aggressive reaction in Erithacus rubecula, the European robin).

sign stimulus(releaser) Part of a stimulus that is sufficient to evoke a behavioural response in an animal (e.g. the patch of red colour that provokes an aggressive reaction in Erithacus rubecula, the European robin).