Are the birds really following only seven neighbours?

Each bird in the game reacts to its nearest few birds (seven by default, set by the bottom dial), as measured in real starling flocks. Nobody plans the big swirling shapes. They fall out of those local rules.

Why does the flock fall apart when I lower the neighbours dial?

With only one or two neighbours, information can’t spread through the flock, so small groups drift apart. Push it back to about seven and the flock pulls itself together again.

How many birds are on screen?

About 4,200 on a laptop, up to 5,200 on a big monitor and 2,400 on a phone. Slower devices get fewer, because a stuttering flock looks wrong. Real murmurations can be tens or hundreds of times bigger.

When can I see a real murmuration?

In Britain and much of Europe, from about October to March, in the half hour before sunset over reed beds, piers and city roosts.

Murmuration

Thousands of starlings, one falcon. Make the sky ripple. Back to the game

How to play

You are a peregrine falcon. Move the pointer (or drag a finger) near the flock and the starlings closest to you panic and swerve, and the panic spreads from bird to bird as a dark wave. Click or tap to dive: the falcon stoops into the flock and blasts a hole in it. On a keyboard, the arrow keys fly the falcon and D dives (Space works too once you've clicked the sky). The “rules” tab holds dials for the three simple rules every bird follows, and for how many neighbours each one watches. Tick off the evening's goals before the sun goes down, then watch the flock pour into the reeds to roost. Finish all six and the flock has a surprise for you. The next evening brings six new goals, and the camera stamp saves a postcard of the sky.

Why starlings murmurate

A murmuration is a huge flock of common starlings twisting over its roost at dusk, mostly in autumn and winter. Flocks range from a few hundred birds to hundreds of thousands. Some of the most famous gather over the reed beds of the Somerset Levels in England, over the city of Rome in winter, and over the marshes of Denmark’s Wadden Sea, where the spectacle is called “sort sol” (black sun). The best-supported explanation is safety in numbers: falcons and sparrowhawks hunt starlings at roosts, a single bird in a dense, shifting crowd is hard to pick out, and a 2017 citizen-science study found murmurations were bigger and lasted longer when a predator was around. Gathering before dark may also help birds find a warm, sheltered roost together.

Seven neighbours

In 2008 a team in Rome filmed flocks with several cameras and rebuilt every bird’s position in 3D. They found that each starling reacts to a fixed number of nearest neighbours, about six or seven, no matter how far away they are, rather than to every bird within a set distance. This topological rule keeps the flock together even as it stretches and squeezes. Later work suggested that about seven neighbours is the best trade-off between staying in agreement and the effort of paying attention. Each bird here follows the classic “boids” rules from Craig Reynolds’ 1986 flocking simulation (stay apart, match your neighbours’ heading, stick together) but only with its nearest few neighbours, just like a real starling.

Waves of panic

In a real flock, the change in one bird’s direction is correlated with birds right across the flock, however big it is, which physicists call scale-free correlation. That is why a falcon’s attack on one edge can send a ripple through the whole murmuration within a second or so. From below, birds turning together show the sky a different side of their bodies, and the ripple looks like a dark band sweeping through the flock.

Questions people ask

Are the birds really following only seven neighbours?: Each bird in the game reacts to its nearest few birds (seven by default, set by the bottom dial), as measured in real starling flocks. Nobody plans the big swirling shapes. They fall out of those local rules.
Why does the flock fall apart when I lower the neighbours dial?: With only one or two neighbours, information can’t spread through the flock, so small groups drift apart. Push it back to about seven and the flock pulls itself together again.
How many birds are on screen?: About 4,200 on a laptop, up to 5,200 on a big monitor and 2,400 on a phone. Slower devices get fewer, because a stuttering flock looks wrong. Real murmurations can be tens or hundreds of times bigger.
When can I see a real murmuration?: In Britain and much of Europe, from about October to March, in the half hour before sunset over reed beds, piers and city roosts.