Experiments

Imprinting studies conducted with mammal and bird species are much easier
because the researcher has the freedom to conduct controlled experiments
that test many different variables, thereby identifying the factors that
influence an individual animal’s ability to imprint. For bird species, a famous
experiment is the moving ball experiment. A newly hatched chick is
isolated in a chamber within which a suspended ball revolves around the
center of the chamber. The researcher can test not only movement as an imprinting
trigger but also other variables, such as critical imprinting time after
hatching, color as an imprinting factor, and variations in the shape of the
ball as imprinting factors. Other experiments involve switching eggs between
different species (for example, placing a duck egg among geese
eggs).
For mammals, imprinting has been observed in many species, such as humans,
chimpanzees, gorillas, dolphins, elephant seals, wolves, and cattle. In
most of these species, the failure of a mother to come into contact with its
newborn almost always results in rejection of the child. In species such as
elephant seals, smell is the primary means by which a mother identifies its
pups. Maternal imprinting is of critical importance in a mammalian child’s
subsequent social development. Replacement of a newborn monkey’s natural
mother with a “doll” substitute leads to irreparable damage; the infant is
socially and sexually repressed in its later life encounters with other monkeys.
These and other studies establish imprinting as a required learning behavior
for the successful survival and socialization of all birds and nonhuman
mammals.