To examine the effects of early visual experience on preference for biological motion, newly-hatched chicks were exposed to a point-light animation (a visual stimulus composed of identical light-points) depicting features of a hen; a walking hen (a biological motion stimulus), a rotating hen (a non-biological motion stimulus), a pendulum stimulus, a random motion stimulus and a stationary pattern. Chicks were then tested in a binary choice task, choosing between walking-hen and rotating-hen stimuli. Males exhibited a preference for biological motion if they had been trained with any animation except the stationary pattern stimulus, suggesting that the biological motion preference was not learned, but induced by motion stimuli. We found a significant positive correlation between the number of approaches in training and the preference in the test, but locomotion alone did not cause preference to biological motion. In contrast, females exhibited a particularly strong preference for walking-hen stimuli, but only when they had been trained with it. Furthermore, females (but not males) trained with random motion showed a preference for walking-hen over walking-cat (a biological-motion animation depicting a cat), possibly suggesting that females are choosier than males. Chicks trained with a stationary pattern and untrained controls did not show a significant preference. The induction of biological motion preference is discussed in terms of possible ecological background of the sex differences.3