Oystercatcher flock in flight over water.

Why birds flock together

How do birds manage to fly so closely together without colliding, and what are the benefits of doing so?

Birds of a feather flock together

At this time of year, our skies can be compared to Heathrow Airport on a busy day as flocks of birds arrive from and depart to warmer climes.

But how do they manage to fly so closely together without colliding? And what are the benefits of doing so - in the air and on the ground?

First, a bit of Ancient Greek for you: the act of any groups of animals coming together in unison is technically known as allelomimesis. And in wild bird populations such gatherings can often number thousands or even - incredibly - millions of birds!

The Greek word 'allelo' describes mutual relation to one another, and 'memesis' (also Greek) denotes imitation or mimicry. 

In short, birds will often copy the actions of their immediate neighbours. They want to keep up with the Joneses too!

Bar-tailed godwits Limosa lapponica, flock at high tide, Firth of Forth, Scotland

Safety in numbers

A larger group of birds boasts a much better chance of spotting a predator, or other potential threat, than a single bird has. 

A group of birds may also be able to confuse or overwhelm a predator through 'mobbing' (when birds attack or chase a would-be predator, to drive it away) or agile flight. 

Staying in a flock presents a predator with more possible targets too, which lowers the danger for any single bird.

Knot Calidris canutus at a high tide wader roost at Freiston Shore RSPB reserve. Also in the flock are Dunlin Calidris alpina. The Wash. Lincolnshire, England.

Knots in flight

Knots fly in close formation to avoid predators

Knots fly in close formation to avoid predators

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Knots video screenshot

Faster food foraging

Birds do not engage in any behaviour that does not bring them a benefit for survival in some way. 

For example birds, such as pink-footed geese  often form flocks to forage, which allows them to take advantage of the same food supplies. 

Feeding in a group also gives more birds the opportunity to find a food source that one bird has already located.

Pink footed geese Anser brachyrhyncus, in flight past wind turbines, Near Diepholz, Lower Saxony, Germany,

Clubbing together

Some birds also choose to nest close together to take advantage of 'safety in numbers'.

In a colony, each nest is carefully tended to by parent birds caring for their young. 

But, at the same time, groups of birds can take advantage of the benefits of being part of a close-knit group to protect themselves and their vulnerable chicks against predators. 

Birds that do not nest colonially may also still form flocks, and juvenile birds from a first brood will sometimes contribute to raising their late-season siblings.

Blackwit flock, Kilmoluaig

Flying V

When birds fly in flocks, they often arrange themselves in specific shapes or formations.

Such formations, which can take the form of a 'V' shape, often take advantage of changing wind patterns based on the number of birds in the flock and how each bird's wings create different currents. 

This allows them to use the surrounding air in the most energy-efficient way, just like the aerodynamic shape of an aeroplane is designed to do. 

Such formations can also increase the distance birds can fly without rest, which is particularly crucial during long migrations.

Geese

Keeping warm

In winter, flocks can share the benefit of communal warmth to survive cold temperatures, such as the common scoter. 

Many small birds will share the same tiny roost space to keep warm, often in bird boxes, hollow trees or other similar spaces. 

And large flocks may congregate in a single tree to share their body heat, too.

In short, there's much more to a flock of birds than first meets the eye!

A pair of common scoters, on breeding grounds at Forsinard RSPB reserve

Starling murmuration

A flock of starlings participate in a spectacular aerial display

A flock of starlings participate in a spectacular aerial display

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Starling murmuration screenshot