With behavioral imprinting—a form of which is termed parental imprinting—a newly hatched or newborn animal is able to recognize its own parents from among other individuals of the same species. This process helps to ensure that the young will not become separated from their parents, even among large flocks or herds of similar animals.
Imprinting occurs during a sensitive period shortly after hatching, corresponding to a time when the chicks are near the nest and unlikely to encounter adults other than their parents. Many behavioral scientists assert that once an animal has imprinted on an object, it is never forgotten and the animal cannot imprint on any other object. Thus even when the chicks begin to encounter other animals they remain with their parents.
Imprinting was first studied in depth by Austrian zoologist Konrad Lorenz (1903–1989), who observed the process in ducks and geese. Lorenz found 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. In 1973, Lorenz's work earned a share of the Nobel Prize for Physiology and Medicine.
The effects of the imprinting process carry over into the adult life of the animal as well. In many cases it has been shown that the object imprinted upon as a hatchling determines the mating and courtship behaviors of the adult. Many species will avoid social contact with animals dissimilar to the one to which they have imprinted. Under normal circumstances, this helps prevent breeding between different species. Under artificial conditions, an animal which has imprinted on an individual of a different species will often attempt to court a member of that species later in life.
Imprinting in animals 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. Imprinting also occurs in humans to at least some extent. An infant separated from its mother for a prolonged period during its first year may develop serious mental retardation. Irreparable damage and even death may result from a separation of several months.