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A releaser is a stimulus from one animal to another, which causes a particular response. The releaser, or sign stimulus triggers an innate releasing mechanism in the receiver. The receiver then does its response, the fixed action pattern (FAP).

This kind of system is inherited by both animals. Example: a fledgling bird does its releaser, say it squawks and opens its beak wide, showing bright red inside throat. This triggers the adult to cough up food stored in its gullet. Both 'partners' are behaving instinctually with inherited behaviours: these are not learnt during life. A FAP can truly be said to be 'hard-wired': a specific stimulus nearly always results in the same behavioral response.[1]

Another behavious system is the 'dances' of water birds such as the Great Crested Grebe. They pair for life, and 'dance' whenever a pair meet up after an absence, and on other occasions. The dances are quite complex, and were first described fully by Julian Huxley.[2] Here the meeting is the releaser, and both partners do the fixed action pattern. The function of the system is a little unclear, but it has something to do with reinforcing the pair's bond.

It is not necessary for both partners to benefit, nor to be of the same species. Some moths instantly fold their wings and drop to the ground if they encounter bat ultrasonic signals. This helps helps the moths, but obviously not the bats. In turn, some bats turn off the sound blips when they hear a moth, and glide in the last few feet. This also is an inherited behaviour.[3] This example may be better described as a reflex action.


  1. ^ Tinbergen N. 1951. The study of instinct. Oxford University Press.
  2. Huxley, Julian 1914. The courtship of the Great Crested Grebe. Proceedings of the Zoological Society, London. Reprinted by Jonathan Cape, London 1968, with a forword by Desmond Morris.
  3. Alcock, John 2005. Animal behavior: an evolutionary approach. 6th ed, Sinauer Associates. ISBN 0878930051