Owls have been around since the Miocene era, which occurred about 38 – 54 million years ago. One of the reasons owls have been so successful has because they evolved to fill a niche – hunting at night, even moonless nights. Their huge eyes and extra-sensitive hearing helps them navigate in complete darkness.
But perhaps their most successful adaptation has been their method of silent flight. Not only does this silence mask their approach, it makes owls better able to hear even the softest noises produced from their prey. The key to an owl’s silent flight is its ability to fly without beating its wings as often as most other bird species.
Primary Feathers Designed for Stealth
Primary feathers are sometimes called “fingertip feathers” because their position on a bird’s wing is similar to the position of fingers on a primate. Primary feathers are long, narrow and at the edge of the wing. In owls, primary feathers are shaped slightly differently than for most birds. The feathers are shaped like a toothed hair comb.
Flying noise is caused by turbulence during wing beats. This happens when the feathers moving through air currents caused by the flying bird slicing through the air. But when air goes through an owl’s primary feathers, the current is cut up into many small slices, dulling noise caused by air turbulence. Combine these feathers with a broad wing and a predator can fly long stretches without beating their wings.
Body Feathers Muffle Noise
Feathers help to keep in warmth and keep out sound. The more feathers a bird has, the better its ability to fly quietly. Owls have far more feathers than any bird of similar size. Part of this feathery arsenal includes thin downy feathers along the wings and legs. The down helps to muffle sound produced by turbulence.
The down feathers are also longer and thinner at the edge, similar to the shape of primary feathers. All flight feathers have an upper surface that feels velvety. This helps feathers slide and rub over each other quietly.
Barn Owl Flight
Barn owls are particularly quiet night fliers because they can slowly glide without the need to flap their wings as often as most other birds. They are able to glide so well because of the long curvature of their wings. One wing beat helps raise a barn owl higher than most other birds – even some other owls.
Barn owl wings achieve this life because the air flow goes over the top of the wing. In most other birds, the air can go partially through wings or outer edge feathers. When air can go through the wings, the bird cannot generate enough pressure to create the same lift that a barn owl can. Barn owl wings are being minutely studied by aircraft designers to try and mimic this silent flight. So far, they have not been successful.