Why do flocks of birds dive and whirl together in the sky?

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A flock of thousands of shape-shifting starlings, called murmuration, is amazing to see. No less than 750,000 birds join the flight. Birds disperse and congregate. The herd separates and merges again. The whispers constantly change direction, rising a few hundred feet, then tumbling down to almost crash to the ground. They look like swirling drops, make teardrops, figure eights, columns and other shapes. A whisper can travel fast – starlings fly up to 80 km/h.

the European or common starling, like many birds, form groups called flocks when foraging or migrating. But a whisper is different. This particular type of flock is named for the sound of a low murmur it makes from thousands of wing beats and soft flight calls.

The murmurs form about an hour before sunset in the fall, winter, and early spring when the birds are close to where they will roost. After perhaps 45 minutes of this spectacular aerial spectacle, the birds all drop to their roosts for the night.

Photos: The bewitching dance of the starlings

Whisper theories

Unlike the V formations of migratory geesewhispers bring no aerodynamic advantage.

Scientists say a whisper is a visual invitation to attract other starlings to join a group of nocturnal roosts. One theory is that spending the night together keep the starlings warm because they share their body heat. It could also reduce the risk of an individual bird being eaten overnight by a predator such as an owl or marten.

This dilution effect could be part of the reason the murmurs occur: the more starlings there are in the flock, the lower the risk of a bird being the one caught by a predator. Predators are more likely to grab the nearest prey, so the whirlwind of a whisper can occur as individual birds attempt to move towards the safer middle of the crowd. Scientists call it the selfish herd effect.

A whisper of starlings can be something to shout

Of course, the more birds there are in a flock, the more eyes and ears there are to detect the predator before it is too late.

And a gigantic mass of whirling, whirling birds can do it difficult to focus on a single target. A falcon or a hawk can get confused and distracted by tricky wave patterns in the movements of the murmur. You also have to be careful not to collide with the herd and injure yourself.

Finished 3,000 volunteer citizen scientists reported spotting whispers in a recent study. A third of them saw a raptor attacking the whisper. This observation suggests that murmurs form to help protect birds from predators – but it’s also possible that a huge murmur was what attracted a hawk, for example, in the first place.

Whispers have no leader and follow no plan. Instead, scientists say the movements are coordinated by starlings observing what others are doing around them. The birds in the middle can see through the herd on all sides to its edge and beyond. Somehow they keep track of how the herd as a whole is moving and adjust accordingly.

To know what’s going on inside the whispers, some researchers film them using multiple cameras at the same time. Then they use computer programs to track the movements of individual starlings and create 3D models of the flock.

Check out this flock of starlings doing laps around the National Mall

The videos reveal that the birds aren’t as dense as they might appear from the ground; there is room for manoeuvre. Starlings are closer to their side neighbors than those in front or behind. Starlings on the edge frequently move deeper into the flock.

Mathematicians and computer scientists try to create virtual whispers using rules that birds might follow in a flock – such as moving in the same direction as their neighbour, staying close and not colliding. From these simulations, it seems that each bird must follow seven neighbors and adjust according to what they’re doing to keep the whisper from collapsing into a chaotic mess. And they do all of this by flying as fast as they can.

Watch starlings fly together in vast, dancing “whispers”

Large schools of fish can appear to behave like whispers, as can groups of certain swarming insects, including bees. All of these synchronized movements can occur so quickly within herds, swarms and schools that some scientists once thought it needed animal ESP.

Biologists, mathematicians, physicists, computer scientists and engineers are all working to understand how animals perform these displays. Curiosity drives this research, of course. But it can also have practical applications, like helping to develop autonomous vehicles that can travel in close formation and work in coordinated groups without colliding.

Langen is a professor of biology at Clarkson University.

This article was originally published on laconversation.com.

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