From a very early age, flocks of birds flew as a whole, curious about how they could fly in groups. The flocks of birds not only show agility, but also show off their speed and coordination. How do they achieve complete coordination in extremely fast group flights and sharp turns? What's the secret?
Starlings stage bird wave spectacles to avoid birds of prey attacks. In the Kurustai Grassland of Xinjiang, thousands of purple-winged starlings constantly change their formation in the air to avoid the attack of prairie harriers and other birds of prey, sometimes like a butterfly, sometimes into feathers, and sometimes like a large bird, as if someone directed them to "paint" in the air, with neat movements and orderly formations. (Photo by Xu Chuanhui)
A group of black-bellied sandpipers hovered at high speed over the swamp until a grey-backed falcon appeared, and at the same moment they turned, the bright white buttocks of the black-bellied sandpipers flashing, rearranging the procession into an hourglass shape at an alarming speed. The distant sky was filled with the chirping of flocks of starlings, ten thousand or more, obscuring the sky on the horizon like a dancing jellyfish.
<h1 class="pgc-h-arrow-right" data-track="5" > why birds fly in flocks</h1>
From a very early age, flocks of birds flew as a whole and were curious about how they could fly in groups. The ancient Romans believed that the flying of birds in flocks was a masterpiece of God, and they were guided by God in flight in order to be consistent with all birds and fly at will. Scientists in the early 20th century, much like the ancient Romans, explored the telepathy of birds, arguing that only a collective mind could act together.
Of course, many birds flock to flocks, but only a few actually fly together. In the 1970s, Frank Heppner, a biologist at the University of Rhode Island in the United States, proposed the concept of so-called "flying groups": that is, highly organized routes or clusters. Pelicans, geese and other waterfowl form a "one" or "human" glyph, presumably to use aerodynamics to save energy. However, the most impressive flocks of birds should be said to be those that form large, irregularly shaped groups, such as starlings, sandpipers, and blackbirds. How fast are flocks of birds? They typically fly at speeds of 64 km/h or more, and in dense groups, the space between them may be only a little more than the length of their bodies. However, flocks of birds can make amazing sharp turns, and in the eyes of humans, the movements are completely coordinated. Imagine being on the highway and you're on the highway, along with all the high-speed drivers around you, making dodging moves that aren't rehearsed in advance, and you'll be able to see the difficulties.
No wonder observers have been looking for explanations. Hepner, who has been studying pigeons flying in groups for more than 30 years, believes that flocks of birds fly through some sort of nervous system-based "bioelectricity" that communicates.
Today, however, technological innovations ranging from high-speed photography to computer simulations have enabled biologists to observe and analyze flocks of birds like never before. Scientists in other disciplines, including mathematicians, physicists, and even economists, have developed a new interest in this phenomenon. As a result, researchers are closer than ever to the truth of group flight.
"There's still a lot of things we don't know right now, but I think we're moving in the right direction and we're going to know in the next 5 years how birds fly in organized flocks and why they do it," Hepner said. ”
The anti-billed sandpipers made their homes in groups and flew in formations. A group of anti-billed sandpipers flew in the Hunan Ji Wetland National Nature Reserve in Poyang, Jiangxi, and formed a group to settle down and fly in formation. (Yan Xian, Bird Net, Early Bird)
<h1 class="pgc-h-arrow-right" data-track="43" > birds who fall alone are more dangerous</h1>
On some level, the purpose of collective action of herds of animals is obvious, whether it is ducks, wildebeest, herring, or social insects. More eyes and ears means an increased chance of finding food, as does the likelihood of spotting an aggressor in time.
When predators swoop in, flocks of birds respond quickly. Many studies have shown that individuals in group action are more vulnerable when they are left alone. This is largely attributable to the deceptiveness created by collective action. Through the rapid rotation of the group or the simple sideways of individuals along the axis, the black-bellied sandpiper is able to change the appearance of its feathers from black to bright white, creating a rapid flash effect that may frighten or confuse predators. Studies have shown that the grey-backed falcon is most successful in chasing individuals in the process of hunting coastal birds. It is true that falcons will catch up closely with crowded black-bellied sandpipers and other shorebirds, but when an attack causes a bird to fall alone, the success rate of the hunt increases dramatically. In other words, number means safety, and birds that stay together tend to survive together. Italian ornithologist Claudio Carere, who worked on a collaborative study of flocks of starlings in Rome, argues that "it's always more dangerous to be left alone." ”
British evolutionary biologist William Hamilton coined the term "selfish clusters" in 1971 to describe this phenomenon. He wrote that the actions of every group member were motivated by simple self-interest. When a predator approaches a group, all individuals in the group move to the safest place, the middle of the group, to reduce the risk of being caught. Observations of juvenile shorebirds suggest that it can take a while to grasp this, as they only learn to form cohesive groups over time. As they do, natural selection determines that birds that are least adept at coexistence with groups are most likely to be caught by predators.
The "bird wave" of the coastal wetland of Hanjiangkou in Shantou, Guangdong Province. At the peak of annual spring migration, birds migrating north from Australia and Southeast Asia come to Shantou one after another, stop at the "transit station" of the Hanjiangkou wetland and replenish their physical strength, and then embark on a long journey to Siberia and other northern breeding grounds. (Courtesy of Visual China)
<h1 class="pgc-h-arrow-right" data-track="44" > flocks of birds flying from the support of order</h1>
Self-interest can explain many observed state of group movement, such as density. But it doesn't explain how birds get the information they need to move in sync and avoid predators. It is impossible for every bird in the group to see a fast-flying falcon at the same time. So how can they possibly know which direction to move to avoid danger? Scientists have found clues in their studies of fish stocks. Many group species in the ocean can also move as complexly as the most cohesive flocks of birds, and they are easier to study because schools of fish can be observed and photographed in open aquariums. In the 1960s, Russian biologist Dmitrii Radakov tested schools of fish and found that if each fish could simply coordinate with its neighbors, they could successfully avoid predators. He describes that even if only a few individuals know where predators are coming from, they can guide a large school of fish, directing their neighbors and neighbors to follow suit. Unlike flocks of geese that fly in clearly led formations, swarms are democratic, they play a role at the grassroots level, and any grassroots member can initiate a movement that other members will follow.
Radakov's theory was not perfected until the 1980s. That's when computer programmers began creating models that showed how simulated groups of animals responded to the movement of individuals within them. The results showed that each bird only needed to follow 3 simple rules when flying to form a tightly bound group. One is to avoid collisions, the second is to maintain the same speed, and the third is to move in the same direction as your companions. By entering these 3 characteristics into a computer model, you can create a "virtual swarm" of any creature you like. They can change density, change shape, and, like birds in the real world, turn rapidly in tiny spaces. From The Lion King to Finding Nemo, filmmakers use similar software to depict and simulate the real movements of large groups of animals, whether they're galloping wildebeests or floating jellyfish.
The crossing of the Mara River by herds of wildebeest is known as the Crossing of Heaven and is the most powerful scene of the Migration of Wild Animals in East Africa. Large numbers of wildebeest cross the Mara River for migration, and they need to cross the river quickly in groups to avoid crocodiles lurking in the river. (Courtesy of Visual China)
However, the real world doesn't work like software. One problem with the underlying model is that it doesn't adequately explain how flocks of birds react as quickly as they do. This is what Wayne Potts recognized in the late 1970s while still being a graduate student. Potts, now a biologist at the University of Utah, has done exhaustive research on the black-bellied sandpiper in Puget Sound, Washington. By taking images of flocks of birds and analyzing how each bird moved frame by frame, he found a swirling ripple passing through the flock, like a human wave made by spectators in a stadium. He named his discovery the "Cabaret Hypothesis." A dancer waits for his neighbor to move before starting kicking, and likewise, the black-bellied sandpiper observes the many birds around him, not just the nearest companion, looking for clues to the next move. The discovery put an end to the ancient theory of telepathy.
Tens of thousands of migratory birds circle over Jiaozhou Bay for food. In late autumn, as the temperature drops, migratory birds such as the grey-spotted sandpiper, the black-bellied sandpiper, and the white-waisted sandpiper that overwinter in the coastal wetlands around the bay in Qingdao, Shandong Province, are clustered on the coastline, and the scene is spectacular. (Courtesy of Visual China)
<h1 class="pgc-h-arrow-right" data-track="45" > as long as you coordinate with the surrounding 7 birds, millions of birds can gather and disperse</h1>
Thousands of starlings spend the winter in their Roman habitat in flocks each year. Every day before dusk, they fly out of the country olive groves that forage during the day in the dim sky. As American natural literature writer Rachel Carson describes the predictable habits of birds, thousands of birds come together to form dense spherical, oval, cylindrical, and wavy lines that change the shape of their groups in an instant. Starling flocks have infuriated many residents, people are tired of the droppings they leave behind, and many admire their superb air shows.
"When starlings approach their habitat, they are often attacked by falcons, at which point they exhibit surprising group behavior." "They compress and disintegrate, split and merge to form 'waves of terror' — flashing away from the approaching falcon in an instant, looking spectacular," Karel said. ”
In the coastal wetlands of southwestern Denmark, some starling flocks can exceed 1 million in the spring, and locals say they appear as "black suns" in the late afternoon, which darken the sky. But it is still Rome's starlings that are more convenient to study, as one of their main habitats is a park located between the city's central train station and the branch of the National Museum of Rome.
Flocks of starlings gather to change their formations, like mysterious alien visitors. October 2020, Gretna, Scotland, UK. Before nightfall, flocks of starlings gather in the air and circle, changing shapes like mysterious visitors from the sky. Starlings flock together for a variety of reasons, such as reducing the risk of predation while also improving foraging efficiency. (Courtesy of Visual China)
In the last two winters, researchers from the pan-European collaboration StarFLAG recorded hours on the rooftops of the historic Massimo Palace, pointing two linked cameras at thousands of starlings performing aerobatic flights. Some researchers have previously used high-speed stereo photography to analyze the overall structure of bird populations, but this is only suitable for relatively small groups. Once a flock of more than 20 birds is found, its structure is difficult to comb. "You have to say who's who in the photos taken from different cameras, and they look different in different images." Andrea Cavagna, an Italian physicist who works with StarFLAG, said, "It's hard for the human eye to tell, and it's even more impossible when there are thousands of birds." Using software imported from the field of statistical mechanics to explain the material's properties by examining its molecular structure, Kavagna and other physicists have now been able to match up to 2,600 starlings with each other in different photographs. This allows them to map the three-dimensional structure of flocks of birds more precisely than before. On the screen they can see flocks of birds as a solid, round mass and understand them as a sphere, or rather some more complex shape, such as a pancake, a cylinder, or an open cup. They can look at it from any angle and watch it change shape at 10 frames/per second.
The result is a quantifiable injection of observation into a speculative field. By zooming in on the three-dimensional reconstruction, the researchers can understand the spatial relationship between individual starlings in a flock to each other. They found that no matter how dense a group appeared from the outside, its members were not evenly distributed like nodes on the grid. Conversely, like drivers on the highway, there is a lot of space behind and in front of each member. Starlings don't seem to mind their neighbors being around them or above or below, as long as there's space in front of them.
This makes sense, as there is a clear path in the direction of flight, minimizing the likelihood of a collision when a bird needs to suddenly change its flight path, as it would have been when attacked by a falcon. But the real beauty of this spatial asymmetry is that researchers have been able to use it to calculate the number of neighbors that each starling watches closely—a quantitative elaboration of Potts' "cabaret hypothesis." By observing the correlation between the movements of neighboring starlings, they can show that each bird is always concerned about the same number of neighbors, whether they are near or far away.
So how many neighbors are there? Cavagna thought it was six or seven. He noted that starlings in flocks can almost always see more nearby birds, but the number may be closely related to the birds' cognitive abilities. Laboratory tests have shown that pigeons can easily identify up to 6 different objects, but not more. This seemed sufficient, with the mind focused on one or more neighbors, allowing the starlings to maneuver quickly when needed. But limiting the number of neighbors of concern to 6 to 7 may avoid confusing the brain with unreliable or excessive information from more distant birds.
However, it is unclear whether all they do is just spying on their neighbors. Several StarFLAG collaborators at the University of Groningen in the Netherlands have been using these closely watched flocks of birds to calibrate computer models that are more complex than any previous computer model that analyzes population behavior. They are trying to refine the model created by physicists to more accurately reflect the real conditions that starlings face, such as gravity and air turbulence. The researchers are also trying to understand how starlings in flight communicate. While everyone agrees that starlings navigate close by eye, that's probably not all the capabilities they have.
"I think it's a matter of both sound and vision." Karel said, "But no one knows exactly how it works." He thinks the starling can even use the sense of touch from the air currents of its immediate neighbors to guide its direction. Obviously, there is much more to learn from these most ordinary birds.
<h1 class="pgc-h-arrow-right" data-track="46" > the inspiration of bird swarms to humans</h1>
Frank Hepner believes researchers will soon be able to explain many of these mysteries, even as he continues to question some of the most basic assumptions about group behavior. For example, he wondered why the starlings over Rome flew in such spectacular flocks for several minutes before settling down. "If they really want to avoid falcons, why not disappear faster?" What they do is not to avoid predators, but to attract predators. Hepner said. He speculates that some kind of fundamental mathematical-based behavior may have occurred, which physicists call "emergency properties." In this case, the whole is much larger than the sum of the parts. Starlings may simply follow the trend of complex behaviors caused by their individual programming, such as flocks, that are inevitable. For humans, it should be understandable, because we know that this is a simple biological law, such as the primitive instinct of human beings to become interested in brightly colored, moving objects, and also leads to unpredictable and obviously irrational behavior, such as flying thousands of miles to Brownsville to see a golden-crowned daisy.
Hepner said: "It may be because these behaviors are like a logical byproduct of birds following the rules." It's entirely possible that you'll get unpredictable behavior from predictable rules. "Perhaps the starlings of Rome would have inspired people's collective decision-making. Based on this finding, scientists affiliated with the StarFLAG program are studying how voters influence each other's choices and whether the decision to set up a new bank branch in a location constitutes the likelihood of swarming behavior.
For some, this practical application of understanding group behavior may be as valuable as understanding God's intentions. However, their value may be lower than that of identifying how people influence groups. The number of starlings that have wintered in Rome over the past few years has not been that much, but with climate change, coupled with other factors, Rome is making it more suitable for them. But as habitats and food change, many flocks of coastal birds are dwindling.
However, the most typical group behavior revelation may be the exploration of understanding and enjoying the flight of flocks of birds. People want to know how the whole world works, but also want to simply appreciate it. Regardless of the assumptions of the computer models, those twinkling black-bellied sandpipers and starlings that spin fast like clouds of smoke will remain compelling sights, at least to some extent, and they will continue to perform. (Source Forest for Humans, Peter Friederici, a paper by AllAboutBirds column, authorized by The Cornell Ornithology Laboratory, compiled by Jianguo Liu, and edited by Wang Qiang)