Owls

Built for hunting in the dark.

Owls are birds of prey, mostly nocturnal, with a suite of adaptations that make them effective in near-total darkness. Almost every distinctive feature relates to detecting prey by sound or approaching it unheard.

Silent flight

Three features combine. The leading edge of the flight feather is serrated, breaking the air into smaller turbulent streams; the trailing edge is fringed, dispersing them; and the surface carries a velvety down that absorbs remaining sound. The result is flight quiet enough that the owl can still hear its prey while moving — the point is as much about the owl's own hearing as about stealth.

Asymmetric ears

In several species the ear openings sit at different heights on the skull. Sound therefore reaches them at fractionally different times both horizontally and vertically, giving a three-dimensional fix. A barn owl can strike prey under snow or leaf litter using sound alone.

The facial disc and the eyes

The dish of stiff feathers around the face works as a parabolic reflector, funnelling sound to the ears. The eyes are tubular rather than spherical, which maximises light gathering but cannot rotate in the socket — hence the extreme neck mobility, up to 270 degrees, supported by extra vertebrae and a modified blood supply.

Pellets

Indigestible fur and bone are compacted and regurgitated. Dissecting pellets is a standard classroom exercise: the bones identify prey species and give a direct record of diet and of the local small-mammal community.