The Barn Owl has amazing hearing & its heart-shaped facial disc channels sound into its very sensitive assymmetric ears. Essentially it is a mobile acoustic rodent surveyance system & very effective it is too. BUT to be effective the owl must avoid producing any sound from its own plumage. Barn Owls have very soft body feathering which produces no appreciable noise in flight. The big price Barn Owls pay for this adaption is that their body-feathering lacks any real water-repellance properties & so they struggle to hunt in rain. Even short periods of hunting in wet grass leads to soaked ventral feathering & possible hypothermia.