Special elastic and porous feather tips on the trailing edge of an owl's wings are able to absorb and suppress most of the sound vibrations generated during flight, making these nocturnal predators silent while hunting, scientists said at the American Physical Society conference in Pittsburgh.
If we can copy this sound-absorbing mechanism present in the wings of an owl, then we will go far in creating new types of coatings from fibers with variable stiffness, which can be used as a basis for covering the wings and fuselage of aircraft, as well as the sides of ships,” said Justin Jaworski from Lehigh University in Bethlehem (USA).
Jaworski and his colleagues analyzed the wing structure, aerodynamics and acoustic properties of owls' wings from a physics and mathematics perspective in an attempt to uncover the secret to their quietness. Through this analysis, the scientists identified three main features of these wings that could affect their acoustic properties - a ridge of stiff feathers on the leading edge, soft down on the upper part, and elastic and porous feathers on the trailing edge of the wing.
Analyzing their individual contributions to the quietness of an owl's wing, the scientists concluded that the key element in the owls' built-in noise reduction was the feathers on the back of their wings. The wings of ordinary birds, the edge of which is composed of relatively hard and inelastic feathers, produce large number noise.
In the case of owls, as the authors of the article explain, this does not happen, since their feathers become more elastic and porous as they approach the tip, which helps dampen acoustic vibrations. In turn, down and hard feathers in other parts of the wing help suppress noise in other ways, which the scientists plan to study in detail in their next work.
Owls are truly one of the most amazing and unusual species birds. They attract the interest and attention of a large number of researchers. And many people simply admire their beauty and mental abilities.
Owls are endowed with acute hearing and good vision, which allows them to lead a nocturnal lifestyle. Almost all species of owls adhere to it. In addition, their eyes have the ability to see well in low light. During the day, owls prefer to rest somewhere - on tree branches, in crevices, under the roofs of abandoned houses. There are some species of owls that make their own burrows and nests.
The vast majority of owls are sedentary birds, that is, they live in one permanent favorite place. But there are still some species that are migratory. Owls of the sedentary type tend to fiercely and carefully protect their own territory from various dangers, as well as from other predators. But if someone still intends to invade their territory, the owls become very aggressive and will not calm down until they drive away the uninvited guests.
Owls feed on live prey, which they obtain during hunting. The diet of these birds, of course, depends on the area where they live, but usually consists of various rodents (rats, mice, shrews), rabbits, various insects, mountain hares, fish, and snakes.
Owls live in pairs, which can last for years, or even last a lifetime. Owls are faithful and devoted birds. Their reproduction depends on the level of food availability, as well as weather conditions. If the owl has enough food and does not feel the need for it, she lays a very large number of eggs. If there is a shortage of food, then the laying of eggs is limited to one or two. Then the owl hatches the eggs for a long time, and the male brings her food. When the chicks are born, the mother owl does not leave the nest for a long time. But in the third week of their age, the male and female begin to teach the chicks to fly. Soon the chicks master the technique of flight and are already able to feed themselves.
The plumage of owls is very beautiful and unique, the color of which helps them camouflage among nature. Also, thick and soft plumage serves as good protection for owls in cold weather.
Today, many varieties of owls are known - about 150 species. These birds of prey live in all possible natural areas.
For many centuries, the attitude towards owls was purely negative. These birds were considered assistants to sorcerers and the living embodiment of evil. The reason for this was their nocturnal lifestyle, as well as the mercilessness with which the owls overtook their prey during the hunt.
This is what the ancient Roman poet Virgil wrote about owls in the 12th book of the Aeneid, his epic work telling about the legendary Trojan hero Aeneas, who moved to Italy:
I give up the fight. Do not multiply, vile birds,
My horror: I recognize the fatal noise and blows
Your wings. Your arrogant command, O great Jupiter...
In the era of early Christianity, an owl was opposed cross. As a nocturnal creature, the owl has become a symbol of evil spirits and witchcraft in Christianity; its images in the Christian tradition are a symbol of the blindness of unbelief.
Subsequently, the attitude towards the owl changed. And in the 20th century, these animals even began to be studied. In the 21st century, when science is concerned with applied issues, scientists decided to try to understand how owls manage to remain ideal night predators.
Thus, scientists have discovered how the owl's feathers ensure its silent flight and how this information can be used in the design of aircraft. An article talking about this was published in a scientific journal Bioinspired, Biomimetic and Nanobiomaterials .
Researchers were able to establish that these birds have real stealth technology, which allows them to overtake prey undetected.
The fact is that owl feathers absorb aerodynamic noise and suppress vibrations that occur when the bird flaps its wings. During flight, the mechanical energy released by the feathers is converted into heat, which ensures silent flight. To find out, the researchers monitored the flight of long-eared owls, eagle and pigeons using high-speed cameras and lasers. The choice of these three birds was not accidental - the flapping of the wings of each of the three is very similar, but at the same time it is the owls who do it silently.
“The mechanism of silent flight of owls has always interested engineers. Now we need to apply what we have learned for the benefit of society,” said lead author of the study, Professor Jinkui Chu from Dalian University.
According to him, the ability to suppress aerodynamic noise along with dynamic noise makes the owl the queen of winged predators.
However, Chinese scientists are not pioneers in the field of research on owl flights - along with them American researchers speak. Thus, representatives of Cambridge recently said that they were able to understand what was happening to the feathers of these birds.
The trailing edge is of primary importance in the acoustic performance of a wing. In “ordinary” wings it is rigid, which is why the wing creates quite loud sounds in flight. Owls have a solution to this problem: the back edge of their wings is soft and “porous,” which significantly reduces noise levels. But the owls didn’t stop there; their wings have at least two more features that help eliminate secondary noise factors. One of these factors is the roughness of the wing surface, which creates noise when it comes into contact with air currents.
But owls have managed this too: the down of the upper part of the wing forms a rough, but at the same time soft and elastic surface, which is very effective in reducing noise levels.
The researchers are confident that the mechanism by which this structure works is unique and very different from the mechanisms by which known noise absorbers work. To uncover these mechanisms, the researchers developed a model that reflects how noise changes with different down fiber arrangements.
Based on their findings, the scientists designed a coating for windmill blades. It turned out that this makes their work almost silent. At the same time, the aerodynamic properties of the blades turned out to be the same.
Now the researchers are setting themselves a promising but difficult task - to apply the obtained data in the field of aircraft manufacturing and design a silent aircraft based on the technologies being developed.
Directly related to the structure of the feather is a unique adaptation characteristic of the vast majority of owls - silent flight. It gives them the opportunity to quietly approach the victim. The softness of the contour plumage of owls is caused by the requirement of noiseless flight. Even large feathers - flight and tail feathers - are relatively soft on owls.
In addition, along the edge of the outer webs, the terminal barbules are partially uncoupled and form a fringe. For example, in medium-sized owls, the fans extend over three to four millimeters. Thanks to this, the whistle of the air cut by the wing is minimized. The special bend of the fan conceals the rustling sounds that arise from the friction of feathers against each other.
In this regard, it is interesting to note that individual species, for example, the needle-footed owl, which is more characteristic of stalking prey rather than stalking, have plumage that is relatively tight to the body and rigid, like that of diurnal birds birds of prey, The same is observed in northern species, white and hawk owls, forced to hunt in conditions of white nights or polar days. The above also applies to some extent to owls and little owls.
The feather structure of owls hunting for fish deserves special attention. Their flight feathers have practically no developed areas. As a result, the flight of, for example, a fish owl in calm weather can be heard fifty or more meters away. Obviously, this bird does not have to fly silently. After all, the hearing organs of fish are not adapted to detect sounds in the air.
Most owls have a relatively long wing, rounded at the top. There are eleven primary flight feathers, with the first one being underdeveloped and hidden by covert feathers. The secondary flight feathers range from fourteen to eighteen. The tail is relatively short, slightly rounded, usually consisting of twelve tail feathers. The only exceptions are a few of the smallest species of owls, for example, the elf owl, which lives in the deserts of the southern United States and Mexico ( Micrathene whitneyi), which has only ten tail feathers. Here we note that in general the structure of the load-bearing surfaces of owls - the arrangement of covert feathers, the number of tail feathers and flight feathers - is generally similar to that of birds of prey.
Speaking about the flight abilities of owls, it should be noted that they are quite advanced. The flight of owls is, as a rule, very fast and maneuverable, although not always long. In most cases, owls fly low above the ground, often in a line inclined to the ground. In this case, flapping flight is usually alternated with gliding. True, eagle owls living in mountains and gorges, according to K. A. Yudin, using rising currents, sometimes soar in circles in the heights for a long time. But for most owls, and even for the eagle owl, soaring flight is not typical. Yes, they don’t need it: getting food for themselves, looking for prey from above, is the job of daytime birds of prey, and not owls.
Literature: Pukinsky Yu. B. Life of owls. Series: The life of our birds and animals. Vol. 1. L., Publishing house Leningrad. Univ., 1977. 240 p.