Instinct is the inherent inclination of a living organism towards a particular complex behaviour, containing innate (inborn) elements. The simplest example of an instinctive behaviour is a fixed action pattern (FAP), in which a very short to medium length sequence of actions, without variation, are carried out in response to a corresponding clearly defined stimulus.
A leatherback turtle hatchling makes its way to the open ocean.
A wet dog instinctively shakes the water from its fur.
Primitive reflexes
"Fixed action pattern" is an ethological term describing an instinctive behavioral sequence that is highly stereotyped and species-characteristic. Fixed action patterns are said to be produced by the innate releasing mechanism, a "hard-wired" neural network, in response to a sign/key stimulus or releaser. Once released, a fixed action pattern runs to completion.
A 3-spined stickleback like those used in Tinbergen's experiments.
A greylag goose which participates in the described egg-retrieval behavior.
Brood parasites, such as the cuckoo, provide a supernormal stimulus to the parenting species, in this case a common reed warbler.