Why do geese put the word "people" when flying in a team?

Herringbone formation, save your strength?

Among the existing herringbone formation theories, the most popular explanation is "preserving physical strength". In fact, this explanation is still in the hypothetical stage. So far, scientists have no conclusive evidence to support it.

Long-term observation shows that large birds generally choose herringbone or linear arrangement, while small birds often gather together. However, the scientific exploration of the mystery of large-scale bird formation flight dates back to the early 20th century when the Wright brothers just started the aviation era. 19 14, German aerodynamicist Karl? Carl Wieselsberger first put forward the hypothesis that flying geese can save energy after simple calculation. He believes that the flapping of geese's wings will trigger a vortex in the wake, and there is only an upward airflow outside the vortex. If the adjacent geese happen to be in the updraft, their flight will be greatly labor-saving.

From the perspective of top view or front view, we can see that the airflow formed by birds flapping their wings produces a horizontal air vortex, one after another. If the latecomers are located in the rising air vortex, they can fly with this lift. The picture is from lifeomics.com.

This hypothesis has been welcomed by ornithologists since its birth, but it was decades before it was really quantitatively calculated. In 1970, Lissaman and Schollenberger used the increasingly mature aerodynamic theory to give the estimation for the first time. They found that the herringbone formation consisting of 25 geese flew 7 1% more than a single goose. They also concluded that the best herringbone angle is 120 degrees. The result of this research is so exciting that today's textbooks on success and leadership are full of this conclusion, which shows how great leadership is and how efficient teamwork is.

Can it be said that the problem of flying geese in a team will be finalized like this?

Wait a minute! In the research of Rishan and Scollan Berg, they did not give a specific formula and calculation process. Moreover, the model they used is too simplistic: first, assume that these birds are as stiff as fixed-wing aircraft without flapping their wings; At the same time, the difference between smooth wings and furry wings is not considered. Since then, many more in-depth theoretical studies have proved that the energy utilization rate of geese flying in formation is far from as high as mentioned in this paper. No matter how detailed this kind of work is and how complicated the model is, rigorous scientists still criticize these theoretical calculations as too idealistic. It seems that theoretical calculation alone cannot win people's favor.

In the wake of fixed-wing aircraft, there is indeed an updraft outside, but the airflow model of birds flying is much more complicated. The picture is from sciencebuddies.org.

Save effort or not, hypothesis VS argument

Theoretical calculation is not feasible, so scientists began to find another way to study the degree of herringbone angle in field observation data. They think that if aerodynamic advantage is the only reason why geese choose herringbone or herringbone, then geese should ensure that the included angle of herringbone is at the best or close to a fixed number most of the time, so as to avoid flying into herringbone, because in the symmetrical wake, the updraft on one side will be wasted. However, reality once again mercilessly attacked this assumption. The research of radar and optical tracking shows that the herringbone angle of big birds varies from 24 degrees to 122 degrees, and the angle will change greatly during flight. The most puzzling thing is that only 20% of the flight time, they will choose herringbone, and most of the time the word snake array is more popular.

From the video of geese migration, we can see the complexity of their flight formation changes.

In recent ten years, the new technological revolution has greatly deepened our understanding of the phenomenon of bird formation flying. This time, experts in the field of drone control came to join in the fun. With the wide application of Global Hawk and Predator UAVs, the control field began to pay attention to the automatic navigation and control of aircraft. In the process of team flight, the big bird frequently adjusts its flight at a large angle, constantly changing the relative distance between the leading bird and the follower bird without collision. After studying the observation records of large-scale bird flight, Sailor and others found that it is almost impossible for these behaviors to coexist from the control point of view. However, they have not completely blocked this road: if each member of the formation adjusts himself based on the leader and the formation is small enough, it is still possible to complete this task.

So far, the most reliable evidence that herringbone formation has aerodynamic advantages is probably from the experiments of Wei Meisi and others. They trained eight white pelicans to become fans of their motorboats. These white pelicans will fly with their buttocks whenever they see a motorboat. By measuring the pelican's heart rate when flying, the researchers found that the heart rate of the white pelican flying in herringbone was lower than that when flying alone 1 1%- 15%, so they concluded that the birds flying in herringbone saved energy. But some critics jump out and retort that social animals tend to have lower heart rates than lonely animals.

In a word, it is really impossible to draw a clear conclusion whether the flying herringbone can preserve the physical strength of geese during long-distance raids. Perhaps the only way to find the final answer to this question is to train a team of big birds in the wind tunnel. Through the mechanical data of their flight in the wind tunnel, it can be judged whether the formation flight saves physical strength.

The research on formation flying of birds has just started.

Although scientists can't prove that herringbone formation and herringbone formation can save physical strength for long-distance flight, other benefits of this formation form have been confirmed. Ornithologists have found that the eyes of Canada geese are distributed on both sides of the head, covering the range of 128 degrees from front to back. This is consistent with the limit angle of these geese flying in formation. In other words, every wild goose flying in formation can see the leading bird, and the leading bird can also see all the members of the formation. So there is at least one clear reason why these birds choose herringbone and herringbone: in formation flight, each bird can see the whole formation, so as to communicate with each other or better adjust themselves.

Swan formation flies gracefully over the suburbs of Beijing. Do you want to appreciate bird migration's posture? Please see "Let's Go and See: Wild Duck Lake, Another Migration Season" to shoot Hu Ling Rabbit Demon.

Although the phenomenon of bird formation flying is common, it is very difficult to study it. After biologists first set foot in this field, aviation engineers, mathematicians and even physicists gradually set foot in and published their own opinions, including the bolder hypothesis that the herringbone formation of birds originated from static electric field, and there was also an opportunity to appear. In fact, anyone can put forward his own hypothesis. As long as it can stand the verification of scientific experiments and field observations, the hypothesis will have a chance to be widely recognized!