There are at least ten suggested hypotheses for the function of mobbing predators by fish, birds, and mammals. Experiments with captive European blackbirds support one of these-the "cultural transmission hypothesis." Perceiving a mobbing conspecific together with a novel, harmless bird induced blackbirds to mob the innocuous object. The mobbing response persisted during subsequent presentations of the novel bird alone, which was more effectively conditioned than an artificial control object. Enemy recognition could be culturally transmitted along a chain of at least six individuals.