Stimulus enhancement in greylag geese: socially mediated learning of an operant task

We recently observed the spreading of a novel tradition in a flock of semif eral greylag geese,Anser anser: an increasing number of individuals began t o bite and chew the stems of butterbur, Petasites hybridus. Because this be haviour spread particularly fast within families, social learning seemed to be involved. We therefore designed an experiment with hand-reared goslings , which were socially imprinted on humans, to investigate whether and how t he observation of an experienced tutor affects the acquisition of a novel s kill. Goslings had to open the gliding lid of a box to get at a food reward , To each of seven hand-reared observers a human tutor demonstrated where a nd how to open the lid, whereas seven controls remained untutored. All obse rvers learned to perform the task but only one of the controls succeeded. T he observers explored more often at the position shown by the tutor than el sewhere and seemingly learned by trial and error. In contrast, control bird s explored primarily at positions that did not allow them to open the box. These results indicate that in greylag goslings the observation of an exper ienced model facilitates the learning of an operant task. We conclude that stimulus enhancement followed by operant conditioning were the mechanisms i nvolved, which may have accounted for the fast spread of the stem-chewing t radition between family members. (C) 2000 The Association for the Study of Animal Behaviour.