While a naked human would start to thermoregulate when the temperature drops below 27C, many animals and birds can tolerate much colder weather.
Wrens (top left), one of Britain’s smallest birds, huddle together to keep warm; blue tits form flocks in winter with great tits and long-tailed tits; many of the mallards seen in the UK in winter months are migrating visitors from Iceland and northern Europe; grey squirrels have the ability to reduce their body temperature, so saving energy as their metabolism falls
