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Collective Behavior: How Animals Work Together

Studies of birds, fish and ants reveal the hidden ways groups coordinate movement, which might influence engineers designing drone armadas and efficient information flow

By Alexandra Witze, Knowable Magazine

In Frank Schätzing’s 2004 sci-fi novel The Swarm, marine life develops a collective mind of its own. Whales band together to attack ships, while herds of jellyfish overwhelm the shores. It’s as if ocean creatures decided to jointly fight humanity, to try to reclaim their degraded environment.

Scientists say this scenario isn’t made up out of whole cloth. Animals do move in groups governed by the collective. Think of a flock of birds, a parade of ants, a school of fish — all are swarms like those envisioned by Schätzing, if not quite as murderous. “Animals regulate these vast collective structures without any leadership, without any individual animal knowing the whole state of the system,” says Nicholas Ouellette, a civil engineer at Stanford University. “And yet it works fantastically well.”

Researchers are now learning about how these swarms pull off such unusual feats. In the English countryside, birds have two distinct sets of rules for flocking, depending on the purpose of their flight. In Mexican forests, groups of ants have evolved computing-like search strategies to find their way around a disturbed environment. And in a lab in Germany, fish develop personalities that ultimately determine how they influence the rest of the school they are swimming with.

These aren’t just interesting observations about nature. Lessons from the natural world about animal group behavior could help humans better engineer our own future, collectively. Such knowledge could help scientists build drones that coordinate their flight like flocking birds, for instance, design packets of information to flow efficiently like foraging ants, or even develop ways to adapt to climate change like some fish do.

Flocks in flight

Ouellette studies how birds and insects fly, which might seem odd for someone whose background is in statistical physics. But he got interested in collective animal behavior because it lies at the intersection of many different types of science. Physicists see it as a living analog to the movement of points within an interconnected system, such as how particles and matter flow. Biologists see it as a subset of animal behavior. Either way, “it’s intellectually very exciting,” Ouellette says.

So a few years ago he began working with Alex Thornton, a biologist at the University of Exeter, England, who studies jackdaws (Corvus monedula). These highly social birds can travel in large flocks, sometimes mixed with rooks. Thornton and his colleagues track thousands of jackdaws in Cornwall, using multiple high-speed cameras to capture footage of the birds and produce three-dimensional maps of which bird flies where.

Among other discoveries, the scientists reported last year that jackdaws that pair with each other for life behave differently than unpaired birds when flying within a flock. Paired birds interact with fewer neighbors when looking for cues to which direction they should fly. Instead they rely more on their partner for information, which leads them to flap their wings more slowly and thus save energy.

On winter evenings, the jackdaws commute from their foraging grounds back to their nests, often gathering along the way at trees in “staging stops.” As the birds travel together toward their roosts they move in what’s known as a transiting flock.

To explore a different kind of coordinated group behavior, this time near the birds’ nests, Thornton and his colleagues placed a stuffed fox in the middle of a field to frighten the birds. The fox had a remote-controlled robotic bird in its mouth that flapped its wings limply. And the scientists broadcast recordings of other jackdaws making loud, scolding sounds that may signal the presence of a predator.

The fake fox worked. The jackdaws started flying around the fox, though in a completely different pattern than the scientists saw in the transiting flights. “The way the birds interacted with each other, and particularly the way they decided which birds to interact with, changed completely in the two kinds of flocks,” says Ouellette. He and his colleagues reported the findings in November in Nature Communications .

Birds flying within a flock have to decide how many other birds they are going to pay attention to for cues on where to move. In a flock of 100 birds, each bird doesn’t need to pay attention to 99 others — it just needs to figure out how many birds to bother watching.

There are two ways birds can go about this. If they pay attention just to the birds within a fixed distance of them, scientists call that a metric interaction. If the bird pays attention to a certain number of birds nearby, no matter how far away they are, it is called a topological interaction. Flocks operating by metric rules behave differently than flocks operating by topological rules; the density of the flock matters only if it is following metric rules.

The group led by Ouellette and Thornton has shown that transiting flocks operate by topological rules. But the stuffed fox led to flocking by metric rules as the birds freaked out. Why the difference? “We don’t know,” says Ouellette. One possibility is that the birds may be trying to keep a certain distance between themselves and the fox. By doing so they start operating in metric mode, which they then use to govern their distances from other birds as well.

This change in behavior is surprising, he says — and might be transmitted among the animals by visual or sound cues as they fly around, calling to one another.

Algorithmic foraging

For the jackdaws, environment shapes behavior. The same is true for ants, says Deborah Gordon, a biologist at Stanford and author of an article on collective behavior in ants in the 2019 Annual Review of Entomology. She studies several species of ants and how they make collective decisions, such as when and where to forage for food.

All of the roughly 14,000 known ant species live in colonies, and so must share information in their search for food and other resources. Gordon studies how ants develop networks of interactions that allow them to pull this off.

One of her favorite species is the red harvester ant (Pogonomyrmex barbatus), which searches for seeds that are scattered across the landscape. A red harvester colony typically has some foragers waiting in the nest while others venture out for food. Studying these ants in New Mexico, Gordon showed that ants leave the nest at a rate determined by how often foragers return with food. The more food available, the more often foragers return to the nest; this, in turn, kicks off more ants leaving the nest. But if there is little food available, the rate of forager return slows and the whole process throttles down.

In 2012, working with her student Katherine Dektar and Balaji Prabhakar, a computer scientist at Stanford, Gordon calculated how information was flowing among the ants. The researchers found it was similar to the way Internet protocols regulate the rate at which data is transferred depending on how much bandwidth is available for transferring it. The scientists dubbed this naturally produced set of problem-solving rules the “Anternet.” The Anternet information seems to help the colony to forage efficiently.

Since then, Gordon has continued to explore the step-by-step problem-solving rules, or algorithms, that regulate how ants collectively search for food and make their way around the environment. She is now studying a tree-dwelling species from western Mexico known as the turtle ant (Cephalotes goniodontus). These ants travel entirely along tree branches and vines, laying down a pheromone trail behind them so that others can follow. The trails connect the ants’ nests and sources of food, forming a sort of communication network in which junctions in the vegetation serve as nodes.

But that network can be easily broken if, say, a windstorm breaks one of the vines. The ants then have to reestablish the trail connectivity. They do so by exploring and choosing new paths to get them around the break. It’s sort of like the way Google Maps suggests alternate routes to get around a traffic accident.

By mapping many paths and examples of how turtle ants found their way around a break, Gordon and her colleagues identified an algorithm that describes the ants’ behavior. The algorithm may not be the most efficient in any one situation, but it works well to find a new route in many different situations. This suggests that evolution has found ways for ant colonies to adapt to their ever-changing environment.

“Evolution has already done a lot of experiments for us, by shaping the way that the ants work collectively to respond to different kinds of conditions,” she says.

Swimming schools

Jolle Jolles, a behavioral biologist at the University of Konstanz in Germany, has also been thinking about collective behavior in the environment. He studies how the individuality of animals affects how they behave within a group — mostly in the fish species known as the three-spined stickleback (Gasterosteus aculeatus).

Biologists studying collective behavior often choose to use fish, in part because they are relatively easy to work with. It’s a lot easier to raise minnows in a tank than to chase jackdaws around southwestern England or ants through a Mexican forest. Sticklebacks in particular are popular and are hardy enough to survive being washed down a drain, as Jolles knows too well. Perhaps most important, sticklebacks also show a huge range of behavior, both individually and in groups, and are well studied. “They are really great little fish,” he says.

Traits of individual sticklebacks include sociability — how closely a given fish likes to hang out with other fish — and boldness, which is how likely a fish is to take risks to find food. In work published in 2018, Jolles showed that schools of fish made up of randomly selected individuals swam in groups that behaved quite differently from one another, even when tested in different kinds of environments. Some groups swam consistently faster, with the fish more aligned with one another than they were in other randomly assigned groups. That suggests that individual differences among fish helped shape their collective actions. The fish could be picking up on visual cues from other fish, and perhaps relying on information from sensory organs that detect movement and other changes in the water. “These group-level behaviors are a result of individual behaviors,” he says.

In experiments involving 80 fish over a 10-week period, Jolles and his colleagues found that bold fish tended to remain bold, as shown by the time spent away from the deep, sheltered end of a tank to venture into bright, shallow areas and look for food. In contrast, shy fish ventured out more and more as the experiments went on, the team reported last year in Animal Behaviour . That suggests that shy fish are less predictable in their behavior over the long term.

Jolles has also worked with robotic fish to explore his ideas. In recent, soon-to-be-published experiments with collaborators in Berlin, he put guppies into a tank with a robofish. The scientists could program the robofish to display all sorts of behavior, including being extremely social with the guppies. With it, the researchers were able to show that the individual speeds of various guppies — which wouldn’t seem like that important a factor — turned out to be the major force that drove patterns in how the fish schooled together.

Jolles is now trying to expand his ideas to other animals, hoping to find universal laws underlying the collective behavior of species from elephants to killer whales. Such laws could show how different traits, such as boldness in sticklebacks, determine which animals end up leading the group and how the group behaves as a whole.

Collective wisdom

From birds to ants to fish, studies of collective behavior have illuminated the basic workings of many animal species. But there are also broader implications for humans. Engineers can take lessons from animals that swarm effectively together to build better swarms of small robots.

Imagine a set of drones hovering over a dam to inspect it. Like the jackdaws, they have to use some sort of rules to determine how far away to fly from their nearest neighbor. If the wind is calm, they might be able to count neighboring drones, through topological rules, to figure out their best position. But if the wind picks up, disrupting the whole flock, they might need to shift to metric rules to avoid crashing into one another.

And understanding how ants collectively adapt to changes in their network, such as when a tree blows down, could help researchers develop flexible and responsive rules for how robots navigate an unfamiliar and changing environment, such as in a burning building. “That’s a lesson for engineering,” Gordon says.

The behavior of swarming animals could even reveal clues for adapting to perhaps the biggest threat of all: climate change. Jolles plans to soon start tracking several species of fish, including sticklebacks, in mountain rivers in the Spanish Pyrenees that are vulnerable to drought and rising temperatures. By studying individual differences among the fish as well as how they behave collectively, Jolles hopes to learn which of them are most resilient in a changing climate and why. “I want to understand how fish can deal with these harsh conditions to help make predictions for the future,” he says.

Alexandra Witze is a science journalist in Boulder, Colorado.

This article originally appeared in Knowable Magazine on July 29, 2020. Knowable Magazine is an independent journalistic endeavor from Annual Reviews, a nonprofit publisher dedicated to synthesizing and integrating knowledge for the progress of science and the benefit of society. 

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Earth to Birds: Take the Next Left

Scientists have long thought that avian migration is guided by the magnetic field, but how, exactly?  The search has led to three very different hypotheses.

By Sophie Fessl, Knowable Magazine

Every fall, the bar-tailed godwit takes to wing and flies nonstop from Alaska to New Zealand — a journey of 7,000-plus miles. Countless other birds head off too, bound for warmer spots before returning in the spring. How they do it without getting lost remains mysterious to this day.

Scientists are convinced birds must be using some type of biologically based magnetic compass, but they have yet to figure out how such a system would work. Now the field is heating up, and the latest research is pointing away from one long-standing theory and bolstering some intriguing alternatives.

Clues have been piling up for decades. Back in the 1960s, researchers discovered that European robins can somehow sense Earth’s magnetic field. In the decades since, scientists learned that robins and a variety of other bird species use the field, which is created by movement of iron in Earth’s core, as a navigational aid. The birds combine this guide with information deduced from the sun, the stars and geographical landmarks to complete their voyages.

A few long-distance bird migration routes. Image adapted from L. Shyamal / Wikimedia

But a vexing question that remains is what sort of biological receptor birds use to detect the magnetic field.

“Key experiments by a group in Germany definitively showed that a magnetic sense exists. Now, more than 50 years later, we still don’t really understand how it works,” says neuroscientist David Keays of the Research Institute of Molecular Pathology in Vienna.

Today, researchers are focusing on three possible ways that a magnetic sense could work. One idea involves a form of iron with magnetic properties, called magnetite, acting as a sort of compass within cells that rotates to align with the magnetic field. Another contender, known as the radical-pair mechanism, hinges on a chemical reaction in a bird’s eye that is influenced by Earth’s magnetic field. A third hypothesis suggests that as a bird moves through Earth’s magnetic field, small currents are generated in the creature’s inner ear.

In all three of these scenarios, signals are produced and passed on to the bird’s brain to be processed and translated into directions. Here’s a look at each of them.

Testing their metal

The magnetite idea has been studied the longest. Though it is biologically possible — certain kinds of swimming bacteria use the iron mineral to orient themselves — evidence in higher animals remains elusive, with scattered reports that are not always reproducible.

“The history of the magnetite literature in vertebrates is basically, ‘I find magnetite here,’ ‘I find magnetite here,’ ‘I find magnetite here,’ but it’s not getting much further than that yet,” says biologist Henrik Mouritsen, who investigates magnetoreception in European robins and blackcaps and coauthored a 2016 overview of the topic in the Annual Review of Biophysics.

Mouritsen, of the University of Oldenburg in Germany, would like to test the magnetite hypothesis using a classic tool of biologists: Remove something from the animal and see what happens to its behavior. If magnetite is critical for navigation, destroying the magnetite-containing cells would affect the birds’ ability to find their way. But for this research strategy to work, scientists need to know just where to find magnetite in the robins. And even if they find it, “it’s a long way from showing a cell contains iron to showing it’s magnetite connected to nerve tissue that has any biological relevance,” Mouritsen says.

One major knock against the magnetite theory is that a bird’s compass senses only the axis of the magnetic field and not its polarity, says chemist Peter Hore of the University of Oxford, a coauthor on the Annual Reviews paper. Unlike the compass needles used by people, which rely on the magnetic field’s polarity to point toward the magnetic North Pole, birds know which direction the nearest pole is but can’t distinguish between north and south. So when scientists invert the magnetic field in the lab, birds don’t sense a change and continue to head in the same direction.

But magnetite particles would respond to a flipped field by pointing in the opposite direction, just like a compass needle would. If birds were depending on magnetite, they would sense the change and turn around to head in the opposite direction.

The eyes have it?

The weight of evidence gathered by scientists tilts toward another idea known as the radical-pair hypothesis, Hore says. Mouritsen also favors this idea, which is based on a protein in birds’ eyes called cryptochrome. When light hits cryptochrome, reactions within the protein generate a pair of molecules, called a radical pair. The two molecules in the pair each have an odd number of electrons, leaving each with a single, unpaired electron. These two extra electrons can have spins that are in the same (or parallel) direction, or in the opposite (antiparallel) direction, and they can also flip between these two states.

Adult female Amur Falcon in South Africa. Photo by Richard Lowe / birdseye.photo

According to the radical-pair hypothesis, Earth’s magnetic field influences how likely the spins are to be parallel or antiparallel. How those spins are then translated into a compass isn’t certain, but scientists suspect that in a biochemical reaction in the bird’s eye, the two spin states could lead to different amounts of chemical products being made. The products could then influence signals sent from the bird’s retina to its brain, making it aware of the magnetic field.

A mechanism based on radical pairs instead of magnetite could potentially allow birds to detect magnetic fields, Keays agrees. But because the radical-pair system depends on light hitting birds’ eyes, he thinks there is probably more than one mechanism at work. “It seems counterintuitive to have a light-dependent magnetic sensor when you are flying at night,” he says.

Or maybe the ears do

Keays is testing a long-forgotten hypothesis, first proposed in 1882, that as a bird flies through Earth’s magnetic field, tiny electric currents are generated in its ear. This would happen through electromagnetic induction, akin to how a magnet that moves through a coiled wire creates an electric current in the wire. Extremely sensitive receptors would pick up the small voltages induced in the bird’s inner ear and send signals to the brain.

Electromagnetic induction is thought to be plausible in sharks and skates, which can sense electric currents in seawater. That same electrosensory system could potentially function as a sort of biological wire in which currents could be induced, allowing the animals to sense Earth’s magnetic field.

To test whether induction could work in a land animal like birds, Keays built a simple, scaled model of a pigeon’s inner ear: a plastic tube filled with conductive fluid. When he put the model in a rotating magnetic field, sure enough, a small current was induced. Keays suspects the pigeon behavior of rapid head-turning to scan the environment during flight may also serve to boost the voltage in the birds’ ears. He has also discovered a very sensitive electroreceptor in the pigeon’s inner ear, which is exactly where it would be needed for induction to work.

Though scientists in the field are finding many new and intriguing pieces of evidence, the definitive test that will finally reveal how birds “feel” the magnetic field has yet to be devised, Hore says. “What we need is a killer experiment that would have the power to show, once and for all, whether it really is radical pairs and whether it really is cryptochrome. But it’s actually very hard to come up with something.”

Sophie Fessl swapped the fruit fly, her favorite neuroscience model, for pen and paper and is now a freelance science writer based in Vienna. Follow her on Twitter: @brainosoph

This article originally appeared in Knowable Magazine on July 16, 2020. Knowable Magazine is an independent journalistic endeavor from Annual Reviews, a nonprofit publisher dedicated to synthesizing and integrating knowledge for the progress of science and the benefit of society. Sign up for the newsletter.

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The silence of the owls

No one knows exactly how the nocturnal hunters manage their whisper-soft flight, yet it is inspiring the design of quieter airplanes, fans and wind turbines.

By Dana Mackenzie, Knowable Magazine

Every owl fancier has a story of the first time they heard an owl — or, rather, didn’t hear one. It’s unforgettable to see an enormous bird, whose wingspan can reach more than six feet, slipping through the air without even a whisper.

Justin Jaworski’s first close encounter came at a flying exhibition at the Raptor Foundation near Cambridge, England. “They trained the owls to fly very close to the audience,” he says. “My first experience was of ducking to avoid a collision. I heard only a very slight swoosh after it passed.”

Laboratory measurements have shown that the slight swoosh made by a barn owl is below the threshold of human hearing until the owl is about three feet away — a feat of stealth that biologists and engineers are far from completely understanding. But researchers from both disciplines are working to solve the riddle of silent flight — some with the aim of designing quieter fans, turbine blades and airplane wings.

Barn Owl, photo by Steven Cheong / birdseye.photo
Noise produced by a Barn Owl while flying isn’t heard by humans until the bird is three feet away. Photo by Steven Cheong / birdseye.photo

Such owl-inspired innovations can reduce noise by as much as 10 decibels, similar to the difference in noise between a passing truck and a passing car, Jaworski and Nigel Peake write in an overview in the 2020 Annual Review of Fluid Mechanics.

Go gentle

Jaworski, an engineer at Lehigh University in Pennsylvania, is hardly the first scientist to be captivated by the puzzle of silent owl flight. In 1934, Robert Rule Graham — a British pilot and bird connoisseur — called attention to three structures on owl wings that might account for the owls’ silence.

More than 80 years later, his “three traits paradigm,” as Christopher Clark calls it, is still cited in many papers on owl wings. “He clearly knew birds very well, and he was an aeronautical engineer,” says Clark, an ornithologist at the University of California, Riverside. “Science was different in the 1930s. In our age of specialization, you don’t get that combination.”

First, Graham pointed out an unusual structure called the “comb,” which literally looks like a comb projecting forward from the wing’s leading edge. Second, he noted that most of the owl wing is covered with a soft layer of velvety feathers. Finally, he observed that the feathers on the trailing edge of the wing form a ragged fringe.

Most researchers still agree that the comb, the velvet and the fringe combine in some way to reduce noise, but the owl may have more tricks up its sleeve. “When all is said and done, I think we’ll have a number of mechanisms, including Graham’s,” says Clark.

To explain how an owl suppresses noise, it would help to identify where the noise comes from in the first place. For an airplane coming in for a landing, a large part of the noise comes not from the engines but from the flow of air around the plane, especially the sound produced at the trailing edge of the wings. The turbulent air rushing past the exposed edges of the wings translates to the dull roar you hear as the plane flies overhead.

Great Horned Owlets, photo by Jason C Rose
Great Horned Owlets display their soft, velvety feathers. Photo by Jason C Rose / birdseye.photo

One way to reduce this noise would be to make the trailing edge of the wing less hard, more porous and more flexible. This may be the function of the owl wing’s ragged fringes. Jaworski and Peake have mathematically calculated how engineers might use such porosity and elasticity to reduce noise, and how to quantify that diminished din.

Those calculations are supported by wind-tunnel experiments: A variety of porous materials do dial down the noise. Work by Thomas Geyer at Brandenburg University of Technology in Germany has found that a poroelastic wing the size of an owl’s can be about 2 to 5 decibels quieter than a regular wing.

However, says Geyer, the right porous material is crucial; in the wind-tunnel tests, some materials actually increased high-frequency noise. Measurements of owls in flight show that their wings mute only frequencies higher than 1,600 hertz (on a piano, two-and-a-half octaves above middle C). Since this is roughly where the range of rodent hearing begins, it’s the range that an owl would benefit most from suppressing as it hunts for a meal.

Jaworski and Ian Clark (no relation to Christopher) of NASA’s Langley Research Center have attempted to mimic the owl’s velvet by covering a standard airfoil with various kinds of fabric. “The winning textile was a wedding veil,” says Jaworski. However, it may not be necessary to donate your nuptial accessories to science, because the researchers got even better results by attaching tiny plastic 3-D–printed “finlets” to the blades of a wind turbine.

“Over a certain frequency range, we saw a 10-decibel noise reduction,” Jaworski says. “That may not sound like much, but in air acoustics, engineers fight over two or three decibels. Ten decibels is half as noisy. That’s a massive change for any technology.” Siemens, a manufacturer of wind turbines, has apparently been listening, and recently unveiled its second-generation “Dino Tail” turbines that have combs directly inspired by the owl wing.

Feathery enigma

Though owl wings are providing new insights into noise reduction for aeronautical engineering, engineers have had less success describing the physics of owl flight. According to ornithologist Clark, the engineers may not even have identified the most important source of noise in owl aviation.

If you’re trying to build an owl, rather than a wind turbine or an airplane, you’ll notice several differences. Owls have feathers; airplanes don’t. Owls flap their wings; airplanes don’t. There’s a good reason that aeronautical engineers prefer stationary, solid wings to flapping, feathery ones: They are easier to understand.

But if you are a biologist, to ignore flapping is to ignore a fundamental ingredient in avian flight, says Clark. As bird wings flap they change shape, and as they change shape the feathers rub against each other, causing noise. This noise is frictional, not aerodynamic, produced by the contact of solid against solid.

As bird wings flap they change shape, and as they change shape the feathers rub against each other, causing noise.

Ian Clark, ornithologist

In Clark’s view, the purpose of the owl’s velvet and the fringes is to reduce frictional noise between the feathers while flapping. Clark concedes that his argument would be moot if owls glided while hunting, but video evidence shows they do not: They flap when taking off, they flap when landing and they even flap when “coursing” for prey.

And the fringes are not only on the trailing edge of the wing, where the aerodynamic theory would predict them to have the greatest noise-reducing benefit. Fringes also exist on the leading edges of the feathers, where they do not affect aerodynamic noise, as well on some feathers that are not even exposed to the airflow. This suggests that their purpose is not aerodynamic.

Clark says that we may be asking the question backward. Instead of asking why owls are so quiet, we should ask why other birds are so loud. The answer is feathers. “Feathers are amazing structures, and probably the reason birds are so successful,” Clark says. But they come with an evolutionary cost: “If you’re going to build a wing out of feathers, they are going to produce frictional sound.” To become silent hunters, owls evolved special adaptations that reduce this disadvantage.

Long-eared Owl, photo by cheema.ss@gmai.com
Fringes on the edges of owl feathers likely dampen sounds, making them much quieter than feathers with sharp edges. Long-eared Owl, photo by cheema.ss@gmai.com / birdseye.photo

Owls are not the only kind of bird that has solved this problem. Some species of Australian frogmouths have independently developed the same adaptations. These birds are also carnivorous and have wings that are soft and fluffy with combs and ragged fringes. In Graham’s day, people assumed that frogmouths were closely related to owls, but genomic analysis has proved that they are not. While less studied than owls, they too are silent flyers.

“Evolution often takes a quirky path,” Clark says. “One way you can home in on the underlying mechanical principles, and tell them apart from quirks, is with convergent evolution.” When two unrelated animals have the same adaptation, it suggests that the feature confers a benefit — in this case, stealth.

At present, there are two ways to understand owl flight: an engineering view informed by the equations of fluid motion and wind-tunnel experiments, and a biological view based on anatomy, behavior and genomics. A truly integrated story will probably require both. Even engineers realize that idealized studies based on rigid, unfeathered wings are not enough. It’s quite possible that the owl uses its feathers and small shape adjustments of the wing actively, rather than passively, to manipulate airflow. Engineers aren’t even close to understanding this process, which spans several size scales, from the barbs of the feathers to the individual feathers, to the entire wing.

“What is missing to us is the microscopic point of view,” says Roi Gurka of Coastal Carolina University in South Carolina, whose experiments with flying owls have led to beautiful computer simulations of the flow field around a flapping owl wing. “I understand the wing,” he says, but understanding the role individual feather morphology plays in noise reduction is another matter.

While the scientists debate, the barn owl will continue flying as it always has: its face as round and imperturbable as the moon, its ears trained on its next meal and its feathers treading gently on the air.

Dana Mackenzie is a mathematician who went rogue and became a writer. His first book, written at age six or seven, was “The Adventures of Owl.”

This article originally appeared in Knowable Magazine on April 7, 2020. Knowable Magazine is an independent journalistic endeavor from Annual Reviews, a nonprofit publisher dedicated to synthesizing and integrating knowledge for the progress of science and the benefit of society. 

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