Releasers of imprinting: instinctive preferences for liver models and those with painted sign-stimuli

White Leghorn chicks hatched and raised in isolation were tested for their preference to situations where age-mates or silhouettes of age-mates were paired against hens, other adult animals, or silhouettes of hens with various sign-stimuli painted on. Silhouettes with painted sign-stimuli elicit quite different developmental patterns of preference, with the hens of the more complex silhouettes being prepotent. The hen silhouette models increase in prepotency when they are moving, with one exception. A Mallard drake emerged as powerful releasing object, suggesting that its large, yellow beak may be a supernormal stimulus.