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Why do flocks of birds swoop and swirl together in the sky? – Artie W., age 9, Astoria, New York
A shape-shifting flock of thousands of starlings, called a murmuration, is amazing to see. As many as 750,000 birds join together in flight. The birds spread out and come together. The flock splits apart and fuses together again. Murmurations constantly change direction, flying up a few hundred meters, then zooming down to almost crash to the ground. They look like swirling blobs, making teardrops, figure eights, columns and other shapes. A murmuration can move fast – starlings fly up to 50 miles per hour (80 kilometers per hour).
The European or common starling, like many birds, forms groups called flocks when foraging for food or migrating. But a murmuration is different. This special kind of flock is named for the sound of a low murmur it makes from thousands of wingbeats and soft flight calls.
‘Flight of the Starlings’ by Jan van IJken was shot in the Netherlands; the audio lets you hear how a murmuration gets its name.
Murmurations form about an hour before sunset in fall, winter and early spring, when the birds are near where they’ll sleep. After maybe 45 minutes of this spectacular aerial display, the birds all at once drop down into their roost for the night.
Why do starlings form murmurations?
Unlike the V formations of migrating geese, murmurations provide no aerodynamic advantage.
Scientists think a murmuration is a visual invitation to attract other starlings to join a group night roost. One theory is that spending the night together keeps the starlings warmer as they share their body heat. It might also reduce the chance an individual bird would be eaten overnight by a predator such as an owl or marten.
This dilution effect might be part of the reason murmurations happen: The more starlings in the flock, the lower the risk to any one bird of being the one that gets snagged by a predator. Predators are more likely to catch the nearest prey, so the swirling of a murmuration could happen as individual birds try to move toward the safer middle of the crowd. Scientists call this the selfish herd effect.
Of course, the more birds in a flock, the more eyes and ears to detect the predator before it’s too late.
‘Murmuration’ by Sophie Windsor Clive & Liberty Smith.
And a gigantic mass of whirling, swirling birds can make it hard to focus on a single target. A falcon or hawk can get confused and distracted by tricky wave patterns in the murmuration’s movements. It also must be careful not to collide with the flock and get hurt.
