Instincts and Mechanism of Behaviour - Andreas Sofroniou - Bog

An instinct is the mechanism by which animals and humans can perform complex behaviour patterns without learning or conscious effort. Instinctive behaviours are inherited and have evolved to be adaptive, fitting the organism to its particular role.
Instinct is of particular importance in animal behaviours such as courtship, mating, and other reproductive activities. More general behaviours such as feeding and defence may have an instinctive base. Many birds, some grasshoppers, frogs, and a number of other animals have song or call patterns that attract mates and are based upon instinct.
Instinctive behaviours often require a stimulus or releaser to initiate them. The herring-gull chick pecks the red spot on the adult's bill, releasing its instinctive feeding behaviour. A releaser will operate only if conditions, both internal and external to the organism, are suitable.