Why do birds flock together?

Watching as a massive collection of birds float across the sky like an unpredictable wave, it’s difficult to comprehend how birds can fly in formation without the aid of the high- tech location equipment used by aerobatic teams like the Red Arrows.

Such patterns may look like the result of extrasensory communication, but they’re in fact the product of emergent animal group behaviour known as flocking. Every change of direction comes not as a result of an individual member of the flock, but rather of the snap decisions made by those individuals in response to the movements of their neighbours.

To comprehend how it works, in 1986 American computer programmer Craig Reynolds applied simple rules to bird behaviour to simulate flocking in his computer program Boids. The three rules he outlines include the fact that each bird steers itself to avoid crowding or bumping its neighbours (separation), each bird tries to match the average heading of its neighbours (alignment), and that each bird steers towards the average position of its neighbours, maintaining flock structure (cohesion).

1) Leader

Flying in a V formation is a good way to reduce fatigue in the members of the flock and a large or strong bird will take the lead.

2) Followers

Each bird will benefit from the updraft created by the flapping of the bird in front’s wings (which creates currents of circulating air), generating lift for the birds behind to take advantage of.

3) Replacement

When the flock changes direction, a new leader will take the helm.

4) Sick birds

A sick or wounded bird will drop out of formation and one other bird will follow it until it recovers or dies.

5) Fatigue

If the leader becomes tired it will rotate back into formation and another bird will then take the lead.

6) Resistance

If a bird falls out of formation it will notice the extra resistance and immediately get back in line.

Canadian Geese flying in a V-formation

Canadian Geese flying in a V-formation

The benefit of the flock

There are several benefits to flying as a flock. It improves a bird’s chance of survival against predators because a large group of birds is stronger and better protected and with many eyes the flock is far more likely to spot a would-be marauder. Also, the predator will find it harder to concentrate on a single victim, increasing the individual member of the flock’s chance of survival.

Flocking also enables birds to fly further using less energy because when the strong leader bird flaps its wings it creates uplift for the birds behind – each bird (except the leader) is flying in the up-wash from the wing of the bird in front. This enables the flock to use less energy and reduces fatigue.

Top 5 Flocking Facts

1) When to watch

The best time of year to witness flocking is winter as migratory birds prepare to head for warmer climes, and those that stick around for winter will be foraging and roosting together.

2) Honk honk

Sometimes geese at the back of their flock will make honking sounds to encourage the birds ahead to maintain their speed.

3) Sort Sol

Twice a year in Denmark massive flocks of starlings block out the sun during an event called Sort Sol or ‘Black Sun’.

4) Movie sims

Craig Reynolds’ Boids program inspired the film Batman Begins to simulate a swarm of bats. It was also the simulation behind the stampede of wildebeest in The Lion King animation.

5) Big flocks

There are more sub-Saharan red-billed Queleas in the world than any other species and their flocks can comprise tens of thousands – the flock can take hours to pass by.

Discover more amazing facts in the latest issue of How It Works magazine. It’s available from all good retailers, or you can order it online from the ImagineShop. If you have a tablet or smartphone, you can also download the digital version onto your iOS or Android device. To make sure you never miss an issue of How It Works magazine, make sure you subscribe today!

Plus take a look at:

Which bird migrates the furthest in winter?

Which is the smallest bird?

How do birds know when to migrate?