On winter evenings throughout much of Europe and North America, an hour before sunset, thousands of starlings gather in the skies. Before descending to their nighttime roosts, the birds put on one of nature’s most spectacular displays. They pulse, ripple, and wheel as if they were a single entity—an amorphous, shape-shifting creature with the delicate beauty of calligraphic brushstrokes and the erratic chaos of flickering flames.

How could so many birds be so tightly coordinated? That’s a mystery that researchers have sought to solve for more than a century. In 1931, the ornithologist Edmund Selous argued that a starling murmuration, which he described as “a madness in the sky,” could only arise through telepathy. The birds “must think collectively, all at the same time,” he wrote. Like many others, Selous assumed that complex behavior must have equally complex origins. But in the 1980s, programmers and physicists started showing otherwise. They created computer models in which virtual individuals interacted according to deceptively simple rules but nonetheless moved in ways that resembled coordinated flocks. These simulations were compelling, but researchers lacked good data on actual flocks to compare them against. Then, in 2005, a team led by married physicists Andrea Cavagna and Irene Giardina in Rome took a giant leap forward. Over many chilly evenings across three years, they climbed to the rooftop of the Palazzo Massimo to photograph the city’s especially epic murmurations with pairs of cameras. Using these images, they reconstructed the 3D position of each individual in murmurations that included more than 4,000 members.

(Starling murmurations are dazzling, ubiquitous, and puzzling.)

The team has learned that no matter how large the flock, each starling interacts with only seven neighbors, which might be as much as their brains can handle. The exact neighbors change from second to second, but the starlings don’t track these shifting alliances. They merely fly in the same direction as whichever seven birds are nearest, while staying close but not too close. Alignment, attraction, and avoidance: By plugging this trio of rules into a computer model, along with some basic aerodynamics, Charlotte Hemelrijk from the University of Groningen in the Netherlands created a virtual murmuration that resembled the real deal—and matched the data from Rome.

This showed that the starlings need no overarching plan, no leader, and no telepathic hive mind. They barely need to communicate at all. Through the simplest of interactions, playing out over distances of a few feet, the breathtaking, sky-spanning complexity of a murmuration emerges.

Over the past two decades, the data from Rome have continued to reveal surprises. When a starling turns, its new alignment should influence its neighbors, and their neighbors, and so on. But you’d expect that mistakes would slowly creep in and the new directions would get lost, much as in the children’s game of telephone. In fact, errors aren’t magnified by the birds’ movements, but washed away. The flock shows what physicists call scale-free correlations, which “is like a game of telephone where information always arrives at the end, uncorrupted,” Giardina told me. This means that no matter how big the aerial display gets, the movement of each bird affects and is affected by all the others. If one turns, they all turn. Each starling is paying attention to only seven others, but its senses effectively extend across the entire flock, and it can respond to events occurring hundreds of birds away. This is why the flock looks like a single entity: It really does behave like one.

(These birds flock in mesmerizing swarms of thousands—but why is still a mystery.)

Buoyed by these discoveries, researchers have become increasingly ambitious and creative in their quest to understand the details behind murmurations. Hemelrijk and colleagues including Rolf Storms and Marina Papadopoulou have been studying the starlings’ evasive maneuvers by lunging at them with a robot designed to look like a peregrine falcon. “You can’t go into the field and wait for a predator to attack, which might happen one day in two months,” Papadopoulou told me. “The robot fixes that problem.” Using footage from the fauxlcon, she is cataloging maneuvers like the flash expansion, where the flock scatters outward, or the vacuole, where a hole forms within the birds. She’s trying to understand how the patterns arise depending on the falcon’s behavior, the flock’s prior formations, or actions of individual starlings.

Researchers also want to follow flocks over long periods. The Rome data were collected with fixed cameras that photographed the starlings only if they flew into view. As Papadopoulou says, “The flock might be spelling your name outside the frame, but you’re not collecting that data.” Giardina’s colleagues have solved the problem with a new network of rotating cameras that can follow the flocks. Now they just need the starlings.

“Unfortunately, there are much fewer flocks now,” Giardina told me. “Last year was a disaster.” She doesn’t know why Rome’s starlings have declined. The city sees them as a nuisance and employs flashing lights and bullhorns to disperse them. But starlings are also disappearing throughout the rest of their native range. British populations have more than halved in the past 60 years, while Danish numbers have dwindled by 60 percent. Søren Solkær, who took the photographs on these pages, says, “In the past two or three years, I’ve had a very hard time locating very large flocks.” It’s not just starlings either: Within the same time frame, Europe and North America have lost 550 million and 2.9 billion birds, respectively, due to habitat loss and other human-driven causes. On both continents, the commonest birds have suffered some of the greatest losses.

Starlings illustrate the stakes of this decline. They remind us that it is not enough for a species to avoid extinction and merely exist. It must thrive and teem, for many of Earth’s most beautiful phenomena only emerge when living things act together in great numbers, whether that’s a flock of starlings or the network of neurons in the people watching them. “When witnessing a starling murmuration,” Solkær says, “the external phenomenon seems to mirror something inside myself, illuminating the universal bond we have with nature.”

(Watch a mesmerizing swarm of starlings.)

A version of this story appears in the April 2025 issue of National Geographic magazine.