Sign stimulus

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In ethology, an external trigger for a fixed action pattern[1]. Signal stimuli are simple visual cues which usually bring about a fixed action pattern response in a different organism of the same spieces.

An example would be in the mating of stickleback fish. The male turns a bright red/blue colour during the breeding season. This colour change is the fixed action pattern in response to an increasing day length which is the sign stimulus. Another ecological example would include an "egg" being a golf ball or ping-pong ball in the relevant area around a water fowls nest, such as a goose. The "egg" triggers a parental respose in which the water fowl will roll the "egg" back into the nest and attempt to hatch it.

In humans, yawning often triggers or releases yawning in other individuals. This is an example of sign stimulus in humans.

Sign Stimulus - a stimulus which triggers one phase of an instinct