For small birds, flocking and roosting can be an essential means for survival, with long-tailed tits taking it more seriously than most other British birds

Birds of a feather flock together. That old saying makes sense in winter when food supplies are scarce and predators are on the prowl. That’s why many birds leave their territories and join forces now: the more eyes there are watching for danger and searching for food, the safer an individual bird will be.

But few British birds take sociability as seriously as long-tailed tits (Aegithalos caudatus). These bundles of black, white and pink not only flock together, they also roost together and when the breeding season comes will help their relatives to rear their young.

Small birds lose more heat in proportion to their body size than larger ones, and on very cold winter nights, long-tailed tits risk dying if they don’t find a companion. But for these tits this is not a problem, because having spent the day in a flock roaming the countryside, they know exactly who they’ll spend the night with.

These roving flocks are made up of related birds: brothers, sisters, parents, uncles and aunts and when darkness falls, they snuggle up together on a twig, often in a dense bush, to share their body heat and stave off the effects of the cold. Birds take turns on the outside of the huddle to share the burden of roosting in the coolest spots.

It looks like genuine altruism – behaviour of an animal that benefits another at its own expense – but many scientists argue that the birds are being manipulated by their genes, and that by protecting their relatives they also protect their own genetic line.

Whatever the reason, it’s a tactic that seems to work because long-tailed tits are doing well and more than ever are visiting our gardens, particularly enjoying suet balls when on offer.

Winterwatch continues tonight with live reports from the Scottish Highlands. Catch the best of UK winter wildlife on BBC Two at 20:00.

You can also follow BBC Earth on Twitter or like BBC Earth on Facebook.

Illustration by Rose Sanderson / group of long-tailed tits (c) imageBROKER / Alamy