Imprinting is an irreversible form of learning. During the sensitive phase, environmental stimuli are permanently incorporated into the behavioral repertoire. Learning by imprinting occurs without reward or punishment. It is also fundamentally different from learning by experience. There are different forms of imprinting e.g.
Successor imprinting: especially in geese. The chicks of geese must first learn who their mother is after hatching, so they have no innate appearance of the mother. In the first hours after hatching, they prefer to approach all objects in their environment that move and make regular vocalizations. After a few minutes in their proximity, the chicks follow them almost unconditionally. In a natural environment, this is the animal that hatched the eggs and keeps all foreign individuals away from the nest – i.e. the mother. Konrad Lorenz repeatedly made sure that only he himself stayed in the immediate vicinity of chicks after they hatched. As a result, the chicks were imprinted on Lorenz and followed him wherever he went.
Sexual imprinting: Sexual imprinting describes the learning processes of the individual in its early development, which essentially determine the later choice of mate. During the sensitive phase, juveniles learn certain parental traits and develop a later preference to the mate that resembles these parental traits. Another feature is the large time lag between the time of imprinting on the object/trait and the performance of the associated behavior. Konrad Lorenz showed as early as the 1950s that male ducks imprinted on him after hatching did not later accept their female conspecifics as sexual partners. Female ducks, on the other hand, possess an innate knowledge of their male conspecifics – as do both sexes of geese.