Imprinting is a term used in ethology (study of animal behavior) to describe the development of a stable behavioral pattern during a brief period of juvenile life (known as the "sensitive phase") in a social species. It occurs as a result of a timely exposure to a particular stimulus. Imprinting is usually associated with the juvenile's developed recognition of its own species, or of particular individuals within its species (such as its parents). Ethologists have demonstrated that sexual (or species) imprinting and parental imprinting are separate events in the behavioral development of young birds, each with its own sensitive phase.
The concept of imprinting was first discovered by Konrad Lorenz, a German biologist and pioneer in ethology, who recorded the behavior in ducks and geese. Lorenz discovered that a chick will learn to follow the first conspicuous moving object it sees after hatching. Normally, this object would be the mother bird, but in various experiments, ducklings and goslings have imprinted on artificial models of birds, bright red balls, and even human beings.
Imprinting on its parents is a learned behavior, without which a young bird might not be fed sufficiently, or might wander away from its caregiver. Parental imprinting is an especially common learned behavior in precocial birds, which are born in a relatively advanced state of development and leave their nest soon after birth, but are still tended by one or both parents as they move about while foraging. Examples of precocial birds include ducks, geese, swans, grouse, chickens, pheasants, and shorebirds such as sandpipers and plovers.
The effects of the imprinting process carry over into the adult life of the animal as well. It is crucial in the individual's ability to later recognize its own species, participate in successful breeding practices, and flock with the appropriate social group. Experimental studies by ethologists have shown that young birds that are only in contact with other species during this critical period of sexual imprinting will not seek to mate with individuals of their own species. Instead, they will try to mate with an individual of their "foster" species. Inappropriate sexual imprinting can be a problem when individuals of certain endangered species are being raised in captivity. For example, rare whooping cranes (Grus americana) raised by sandhill cranes (G. canadensis) may later have extreme difficulty in mating with individuals of their own species.
Imprinting in mammals is most thoroughly studied in birds, although it is believed to be especially important in the hoofed mammals, which tend to congregate in large herds in which a young animal could easily be separated from its mother. Other organisms, such as salmon, imprint on chemical cues in their environment, and use these to remember the location of their breeding grounds. Atlantic salmon (Salmo salar) are born in freshwater habitats (cool rivers and streams), and later migrate to the ocean to grow into adults. When they are young, the salmon imprint on chemical cues in their natal habitat. When they are adults, the salmon use their chemical memory to find the same breeding river or stream (or at least its vicinity) in which they were born, in order to breed there themselves.
The existence of a critical period for imprinting is a genetically fixed trait in certain species of animals. Learning, however, is a circumstantial experience, being dependent on environmental conditions occurring at a particular time. Learning through imprinting is, therefore, an interesting case of a behavioral interaction between inheritance and opportunity.
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