The barn-owls' main characteristic is the heart-shaped facial disc, formed by stiff feathers. The feathers help to amplify and locate the source of sounds when the bird hunts. Adaptations to the wing feathers eliminate sound caused by flying. This helps both the owl's hearing, and keeps the prey unaware of the owl. To summarise: the owl hunts mainly at dusk and night-time. Its uses sound to detect prey movement: its hearing is sensitive, and its wings are almost silent.