Fixed action pattern

There are six characteristics of fixed action patterns. Fixed action patterns are said to be stereotyped, complex, species-characteristic, released, triggered, and independent of experience. • Stereotyped: Fixed action patterns occur in rigid, predictable, and highly-structured sequences. • Complex: Fixed action patterns are not a simple reflex. They are a complex pattern of behavior. • Species-characteristic: Fixed action patterns occur in all members of a species of a certain sex and/or a given age when they have attained a specific level of arousal. • Released: Fixed action patterns occur in response to a certain sign stimulus or releaser. • Triggered: Once released, a fixed action pattern continues to completion, even when there are changes in the surrounding environment. • Independent of experience: A fixed action pattern is not learned. This is known as a fixed action pattern is complete upon the very first release. ==Sign stimulus==

The sign stimulus, also known as key stimulus or releaser, is the determining feature of a stimulus that produces a response. Sign stimuli are often found when observing a fixed action pattern (FAP) that is an innate behaviour with very little variance in the manner in which the actions are executed. Several examples of sign stimuli can be seen through the observation of animal behaviour in their natural environment. Experimenters have gone into these natural environments to better assess the stimuli and determine the key features of them that elicit a fixed action pattern. Scientists have also observed direct exploitation of sign stimuli in nature among different species of birds. Fixed action patterns are released due to certain external stimuli. These attributes may include color, shape, odor, and sound. A supernormal stimulus leads to an exaggerated response. == Examples ==

Male stickleback mating behavior 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. During the spring mating season, male sticklebacks' ventrum turns red and they establish a territory to build a nest. The sight of the displaced egg is the sign stimulus and elicits the egg-retrieval behavior. 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 egg's displacement that the fixed action pattern occurs. The manipulation of the sign stimulus through a series of experiments can allow scientists to understand what specific component of the stimulus is responsible for 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. == Evolutionary advantages ==

Most behaviors which are both fixed action patterns and occur in more complex animals, are usually essential to the animal's fitness, or in which speed (i.e. an absence of learning) is a factor. For instance, the greylag goose's egg-retrieval behavior is so essential to the survival of its chicks that the fitness of the parent bird is increased by the behavior being relatively invariant. A stickleback will attack any male fish who enters his territory while the female is sexually receptive, reacting to their red color, while the female stickleback triggers behavior in the male resulting in the fertilization of her eggs. == Evolutionary disadvantages ==

, provide a supernormal stimulus to the parenting species, in this case a common reed warbler. Fixed action patterns are predictable, as they are invariable, and therefore can lead to exploitation. Some species have evolved to exploit the fixed action patterns of other species by mimicry of their sign stimuli. A well-known example of this is brood parasitism, where one species will lay its eggs in the nest of another species, which will then parent its young. A nestling will provide higher levels of stimulus with noisier, more energetic behavior, communicating its urgent need for food. == Exceptions ==

There are four exceptions to fixed action pattern rules. Vacuum activity is demonstrated in courtship behavior of ring doves. 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. This can be seen in sticklebacks. Displacement behavior occurs when the fighting and mating urges are frustrated. A male stickleback chasing another male stickleback stops where their two territories meet and dives to the bottom of the tank, picking something up. This behavior resembles that of nest digging during mating season, but is not released by the proper sign stimulus. Graded response Fixed action patterns may vary in intensity instead of being triggered. == References ==