Lessons from bird brains
Eckhard Hess’s research on imprinting helped to popularize an emerging field of research — one
that that explored genetic and learned aspects of early behavior.
by CAthy fAyE
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,
Bateson, P. (2003). The promise
of behavioural biology. Animal
Behaviour, 65, 11–17.
Hess, E.H. (1958). Imprinting
in animals. Scientific American, 198,
Hess, E.H. (1973). Imprinting:
Early experience and the
developmental psychobiology of
attachment. New York: Van Nostrand
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