Why Do Starlings Murmurate? How Huge Flocks Move as One

What is a murmuration?

A murmuration is a huge flock of European starlings wheeling, swooping and changing shape in the sky, usually just before sunset. Flocks range from a few hundred birds to tens of thousands, and the largest roosts hold hundreds of thousands or even more than a million birds. The flock can stretch into ribbons, bunch into a dense ball, split in two and flow back together within seconds.

The word comes from the soft, murmuring rush of thousands of wings beating at once, which can be heard from some distance away. After anywhere from a few minutes to more than half an hour of display, the birds suddenly pour down into their roost in reedbeds, woods, under piers or on city buildings, and chatter noisily as they settle.

Why do starlings murmurate?

Scientists have studied murmurations for decades. The main explanation is protection from predators, but several benefits probably combine.

• Safety in numbers. In a huge flock, the chance of any one bird being caught is tiny. This is called the dilution effect.
• Confusing predators. Peregrine falcons, sparrowhawks and merlins need to single out one target. A dense, constantly shifting mass of birds makes that very difficult, and a sudden wave of turning can throw off an attack. A large citizen-science study in Britain, published in 2017, found that murmurations tended to be larger and last longer when birds of prey were present.
• Warmth at the roost. Sleeping packed together in reedbeds or trees helps the birds stay warm through long winter nights.
• Attracting more birds. A big, visible display may draw in other starlings from the surrounding countryside to the same roost, adding to the safety for everyone.
• Sharing information. Some researchers suggest that roosts let birds learn where good feeding areas are from the birds around them, though this idea is harder to prove.

The peregrine falcon is one of the main predators that attacks murmurations, often diving into the edge of the flock. Watching the flock bulge and ripple away from a hunting falcon is one of the most dramatic parts of the display.

How do thousands of starlings move together?

There is no leader in a murmuration. Each bird follows simple rules: stay close to your neighbors, match their direction and speed, and avoid colliding with them.

In 2008, a team of physicists and biologists in Rome, led by Michele Ballerini and Andrea Cavagna, filmed starling flocks over the city with multiple cameras and reconstructed the three-dimensional position of each bird. They found that each starling pays attention to about six or seven of its nearest neighbors, whatever the distance to them, rather than to all birds within a fixed radius. This lets the flock stay together even as it stretches and compresses.

Later work by the same group showed that a change in direction by one bird can spread across the whole flock almost instantly, passing from neighbor to neighbor like a wave. That is why a murmuration can react as a single unit, and why waves of darker and lighter shading ripple across it as birds tilt their wings.

When do murmurations happen?

In Britain and Ireland murmurations usually begin in October and continue into March. They are biggest from about December to February, when millions of starlings from Scandinavia, the Baltic states and Russia have joined the resident birds for the winter.

Displays happen in the late afternoon, typically starting 30 to 60 minutes before sunset, and are best on calm, dry evenings. In southwestern Denmark, along the Wadden Sea marshes near Tønder and Ribe, flocks of up to a million or more birds gather in March and April as northern starlings head back to their breeding grounds. The Danes call this spectacle sort sol, or “black sun”.

Where to see starling murmurations

Murmurations can appear wherever large roosts form, and their locations can change from year to year. Well-known sites include:

• England: Brighton Palace Pier; the Somerset Levels, around RSPB Ham Wall and Shapwick Heath; RSPB Leighton Moss in Lancashire; and RSPB Minsmere in Suffolk
• Wales: the pier at Aberystwyth
• Scotland: Gretna, near the border with England
• Northern Ireland: the Albert Bridge in Belfast
• Elsewhere in Europe: Rome, where huge flocks gather over the city in winter, and the Danish Wadden Sea in spring

Local wildlife trusts and RSPB reserves often share updates on where roosts are active each winter.

Are murmurations getting smaller?

Starlings have declined steeply in Britain, falling by more than 80 percent between the 1960s and the 2000s, mainly because fewer young birds survive. Winter numbers are still boosted by migrants from the continent, so large murmurations can still be seen. Starlings are not the only birds that gather in huge winter roosts: crows also do, as explained in why do crows gather in huge flocks?. For other collective nouns, see our list of animal group names.