Fixed action pattern

When conducting further experiments, scientists came across the idea of supernormal stimuli. Nikolaas Tinbergen found that incubating geese when given the choice between performing the egg-rolling FAP with an egg versus a full-sized volleyball, they chose the volleyball. These supernormal stimuli, although not naturally occurring, gave insight into the process of natural selection and how it may be that some stimulus features such as the size of the egg result in an increased ability to trigger a FAP.[11]

A 3-spined stickleback like those used in Tinbergen's experiments.

One example of fixed action patterns is the courtship and aggression behaviours of the male stickleback, particularly the three-spined stickleback, during mating season, described in a series of studies by Niko Tinbergen.[4][12] During the spring mating season, male sticklebacks' ventrum turns red and they establish a territory to build a nest.[4] They attack other male sticklebacks that enter their territory, but court females and entice them to enter the nest to lay their eggs.[4] Tinbergen used models of sticklebacks to investigate which features of male and female sticklebacks elicited attack and courtship behavior from male sticklebacks.[4] Tinbergen's main findings were that male sticklebacks responded in a relatively invariant way and attacked even the most crude of models with a red belly, but in contrast, courted a model with a swollen belly.[4] He also found that when presented with both a real male stickleback and a crude model, if the model's stomach was more red, the stickleback would attack the model as opposed to the other real male stickleback.[4]

A greylag goose which participates in the described egg-retrieval behavior.

Another example of a behavior that has been described as a fixed action pattern is the egg-retrieval behavior of the greylag goose, reported in classic studies by Niko Tinbergen and Konrad Lorenz.[5] Like many ground-nesting birds, if an egg becomes displaced from the nest, the greylag rolls it back to the nest with its beak.[5][11][13] The sight of the displaced egg is the sign stimulus and elicits the egg-retrieval behavior.[5] First, the goose fixates its sight on the egg.[5] Next, it extends its neck over the egg.[5] Finally, it rolls the egg back to the nest using the underside of its beak.[5] If the egg is removed from the goose during the performance of egg-rolling, the bird will continue with the behavior, pulling its head back as if an imaginary egg is still being maneuvered.[5] It has been shown that the greylag will also attempt to retrieve other egg-shaped objects, such as a golf ball, door knob, or even a model egg too large to have possibly been laid by the goose itself (i.e. a supernormal stimulus).[14]

The sight of the egg outside of the nest serves as the stimulus in this particular instance because it is only after the recognition of the eggs displacement that the fixed action pattern occurs.[11][15]

The manipulation of the sign stimulus through a series of experiments can allow scientists to understand what specific component of the stimulus is responsible the innate behavioral sequence. If the egg were to be picked up and taken away after it is displaced from the nest, the goose still exhibits the same head moving motion even though there is no egg present.[11] This was put to the test by using objects such as beer cans, and baseballs. Experimenters found that the stimulus merely had to be an object that was large enough in size, convex enough in shape, and comfortable enough for the goose to lay its neck around the edges of the object.[11]

These features that the stimulus has to obtain in order to trigger a resulting FAP were then given the official term of Sign Stimuli. Scientists came to the realization that there must be an innate deciphering method that the goose goes through in order to determine a suitable sign stimulus. This was defined as an innate releasing mechanism (IRM). The goose's IRM when put to the test in the natural world not being manipulated by scientific experimentation is almost always efficient in getting the desired item of an egg back into the nest.[11]

More examples of sign stimuli include:

• The red mark on an adult's beak recognized by the chicks of various gull species.
• Light polarization patterns recognized by mayflies when they are deciding where to drop their eggs.
• The presence of a female sage grouse that causes males to exhibit a strut pattern display in order to attract the female during breeding season.[16]

The exploitation of sign stimuli can be seen when exploring the concept of brood parasitism. Other animals will learn the sign stimuli of different species and use it to manipulate the other animal into doing something for its own benefit. An example of this can be seen in the European cuckoo. This particular species of bird benefits by handing off the task of raising their young to other species of birds who will care for any egg that is found in its nest. In this case the sign stimulus is the presence of the eggs in the nest. If the other bird does not recognize the other bird's egg as foreign, it will continue on caring for it as its own by incubating it and hatching it. Once it is hatched, the young cuckoo ensures for itself a solid upbringing by instinctively pushing its neck around anything that is solid in the nest and pushing it over the edge. Thus classifying the sign stimulus as any solid object. This allows for the cuckoo's unwitting foster parents to have plenty of time to devote to caring for it without any other distractions.[20]

Fixed action patterns become easier to release as time increases between the last release.[8]

After so long without being released, fixed action patterns are released in the absence of the sign stimulus or releaser.[21] Vacuum activity is demonstrated in courtship behavior of ring doves.[22][23] Male blond ring doves isolated from their own species will resort to courting a pigeon, then a human's hand, and finally expressing courtship activity alone in their box, if they are left alone for a long period of time.[22][23]

Fixed action patterns may be performed that are irrelevant to the stimulus present.[24] This can be seen in sticklebacks.[24] Displacement behavior occurs when the fighting and mating urges are frustrated.[24] A male stickleback chasing another male stickleback stops where their two territories meet and dives to the bottom of the tank, picking something up.[24] This behavior resembles that of nest digging during mating season, but is not released by the proper sign stimulus.[24]

Fixed action patterns may vary in intensity instead of being triggered.[8]