Britain’s smallest birdd – the goldcrest, pictured right – weighs just 5g and in extreme cold can lose a fifth of this overnight. ght. Goldcrests often huddle in n a globular mass with theirr tails all sticking out.
Despite a hot-tempered nature, robins will also roost communally in extreme wintry conditions.
A recent study by the BTO and University of East Anglia found that Scottish wrens are, on average, larger than those in milder southern Britain and better able to survive overnight frosts.
Treecreepers, too, suffer greatly in winter – but for them, wind and rain are worse than sheer cold. They squeeze into bark crevices for shelter.