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How Owls Fly Silently

Shashank Nakate
Owls are nocturnal creatures that hunt in stealth mode. Flying silently proves to be advantageous for them during hunting. This BirdEden post provides an explanation on how owls manage to fly silently.

Sound Shifted to Higher Frequency

It is speculated, but not confirmed yet, that the feathers of owls convert the sound energy generated by their wings to a higher level of frequency. The owl's prey cannot hear the sound generated at this frequency. It means the owl can easily operate in stealth mode while it is hunting.
Owls are one of those creatures about whom very little is known. These nocturnal birds are surrounded by a lot of myths. Some say that they are predictors of death, while others believe owls to be wise creatures. Such myths are born out of ignorance. Some of you might already be aware of the fact that owls fly silently.
The silent flight of owls has fascinated researchers for long. These birds possess large wings, which help them attain flight without making any sound. It is not just the wings, but also their legs that are covered in feathers. In short, the whole body of these birds is designed to assist them in flying silently.

Explanation of How Owls Fly Silently

Silent Flight and Structure of Wings

The wings of owls are broad and wide. The large surface area of these wings allows them to float in the air for a relatively longer time, as compared to other birds. Owls possess wings that are denser than most other birds on our planet. The dense wings absorb sound, and therefore, play an important role in making the flight silent.
An object moving through air with substantial speed causes vibrations and pressure waves, which leads to the creation of sound. The air passing above the wings of birds causes these vibrations. In most birds, the vibrations cause a swishing sound. However, for the owls, a silent flight is attained by minimizing or preventing the generation of such pressure waves. The design of the edges of the owl's wings plays an important role in attaining a silent flight.

Serrated Primary Feathers

The primary feathers of an owl's wings are separated from each other. This arrangement helps in absorption of sound. The comb-like serrated margin of the primary feathers of an owl's wings help reduce or break down air turbulence. It is broken down into micro-turbulence - these are small currents or air which do not cause much noise.

Spiciform Arrangement of Fine Hair

The little hair present on the fringe of the trailing feathers prevent the generation of pressure waves. These little hair are not just fine, but also have a tattered arrangement. This kind of arrangement is also referred to as a spiciform (spike-shaped) arrangement. Since the arrangement of these fine hair is irregular in form, it prevents the creation of a swishing sound. This means, the sound gets muffled. The angle of the flow of air also is shifted. The surplus sound is absorbed by the soft surface of the feathers.

Reduction in Friction Noise

The reduction in friction noise generated between the single feathers of an owl's wings is reduced by the velvety surface of the wings. These velvety feathers cover the wings as well as the legs of owls.

Benefit of Flying Silently

The benefit of flying silently is that, the owl can sneak up on their prey. Since it is a nocturnal hunter, this characteristic proves to be of great help for them. A silent flight allows barn owls to listen to the scurrying sound of voles that they hunt for.

Research on the Silent Flight of Owls

Southampton University's professor emeritus of aeronautics and astronautics, Geoffrey Lilley, has worked on the Quiet Aircraft Technology at NASA's Langley Research Center in Hampton, Virginia. Researchers at Cambridge also have studied the phenomenon of the silent flight of owls. Gaining an understanding of this phenomenon should help in designing a conventional aircraft with a silent flight.
Dr. Thomas Bachmann from the Technische Universit├Ąt Darmstadt in Germany, has conducted research on the silent flight of barn owls. He had presented a paper on this subject at one of the annual meetings of the Society for Integrative and Comparative Biology, held in Charleston, South Carolina.
The owl is one mysterious creature of our planet. It is not just its silent flight, but also the forward-facing eyes of these creatures which make it unique among birds. There are a few birds which possess such type of binocular vision. All in all, the owl is an interesting bird to study.