Konrad Lorenz, a notable ethologist (ethology = study of animal behavior), got a group of geese to “imprint” on him.
Imprinting is a process all animals go through (including humans, to some extent) in which a baby becomes heavily attached to a creature—usually the parent—that happens to be near it during birth. The baby then mimics the behavior of the creature it imprinted on.
Dr. Lorenz was the first living thing the geese saw after being born. They therefore imprinted on him. They followed him around as though he was their mother. This imprinting lasted the duration of the geese’s lives.