In 2003, as winter began to creep across the Russian tundra, a man in a hang glider led a small flock of Siberian cranes on a 3,000-mile migration from the Arctic Circle to the Caspian Sea. The birds needed the help. Traditional migratory routes led the endangered birds over the dangerous and war-torn skies of Pakistan and Afghanistan, exposing them to gunfire. And the captive-bred birds simply didn't know how to get to their winter feeding grounds. Italian aviator Angelo d'Arrigo showed them the way — and the cranes followed, thanks to principles of imprinting cleverly harnessed by scientists at the Crane Breeding Centre at the Oka Nature Reserve, near Moscow.
Famously described by zoologist Konrad Lorenz in the 1930s, imprinting occurs when an animal forms an attachment to the first thing it sees upon hatching. Lorenz discovered that newly hatched goslings would follow the first moving object they saw — often Lorenz himself. As a result, he was often trailed by a half-dozen waddling geese as he tended the grounds of his Austrian estate.
Though Lorenz's work spurred interest in the early social attachment of animals, scientists found it difficult to study. Because young animals would often imprint on the first object they saw, imprinting research required complete control of the environment.
In the 1950s, a young psychologist named Eckhard Hess (1916–86) devised an apparatus for just this purpose.
As a young boy in Germany, Hess took an early interest in animals raised in his family's barnyard in East Prussia. Later, when they moved to the suburbs, he began observing animals in nearby forests and fields, often bringing them home with him. When Hess was 11, he and his family immigrated to the United States. He earned a PhD in psychology in 1948 from Johns Hopkins University, then took a position at the University of Chicago, where he remained for the rest of his career.
In the 1950s, Hess and A.O. Ramsay, a high school biology teacher from Maryland, began studying imprinting in the laboratory with papier-mâché mallard ducks fitted with off-center wheels that mimicked waddling. The researchers created a great variety of model ducks to experiment with, including ducks with moving heads and ducks with built-in heaters.
By means of pulleys and cords operated from a distance, Hess and his colleagues released newly hatched ducklings from a small cardboard box. The model duck would emit a sound — either a tape-recorded duck call or a human mimicking one — and move around a runway via a motorized arm. Levers on the runway floor kept track of the ducklings' steps to measure their following behavior. At the end of the experiment, a trap door in the runway's floor returned the ducklings to their box.
With this imprinting apparatus, Hess and his colleagues tested several scenarios. For example, they found that the ducklings could also be imprinted on objects other than papier-mâché decoys. Ducklings would also follow a colored sphere, but imprinting was stronger for blue spheres than for white ones. Hess and Ramsay also tried unsuccessfully to imprint ducklings with auditory cues before they hatched by placing speakers in the incubator or nest. Over the course of many experiments, the researchers found that prime time for imprinting was 13 to 16 hours after hatching.
Like previous imprinting researchers, Hess took his work home with him, raising chickens, geese, starlings, ducks, hamsters, lambs and other animals at his country home in Maryland. He and his wife fed and cared for the animals, and sometimes enlisted the help of household appliances unintended for such purposes. Their first gosling, for example, was hatched in a makeshift incubator that was ordinarily used as a place for the rising of yeast dough. By 1985, he and his wife had raised a population of nearly 100 Canada geese.
Through the work of Lorenz, Hess and others, imprinting research drew wide attention. It shed light on many important and controversial topics of 1950s psychology, most notably the problem of heredity and learning. Imprinting, it seemed, was different from most forms of learning. It appeared irreversible and confined to a critical period, and seemed not to require reinforcement. Later research suggested that imprinting may in fact be reversible and may extend beyond the critical period identified by Lorenz and Hess. Regardless, their findings helped to usher in a new era of research on behaviors that appeared to be genetically determined and learned.
Researchers continue to examine imprinting as an example of tightly constrained learning that involves genetic predispositions. And, as the Italian aviator Angelo d'Arrigo showed, imprinting research has practical applications for conserving endangered species. Sadly, d'Arrigo died in 2006 while performing at an airshow in Sicily. However, the practical applications of imprinting continue to be used for similar projects, including Operation Migration, which is teaching captive-born whooping cranes to follow small aircrafts south for the winter.
Cathy Faye is assistant director of the Center for the History of Psychology at the University of Akron. Katharine S. Milar, PhD, is historical editor for "Time Capsule."
- Bateson, P. (2003). The promise of behavioural biology. Animal Behaviour, 65, 11–17.
- Hess, E.H. (1958). Imprinting in animals. Scientific American, 198, 81–90.
- Hess, E.H. (1973). Imprinting: Early experience and the developmental psychobiology of attachment. New York: Van Nostrand Reinhold Company.
- Hess, E.H. (1985). The wild goose chase. In D.A. Dewsbury (Ed.), Leaders in the study of animal behavior: Autobiographical perspectives (pp. 183–191). Cranberry, NJ: Associated University Presses.