Just as humans have historically gathered during winter, many animals do the same. Animals may not be exchanging presents or decorating their nests and dens but a lot of species become more social in winter – even ones that are normally solitary. Animals have more to worry about this time of year than bickering relatives or the last date for Christmas post. Winter poses severe challenges for wildlife, from freezing temperatures to a scarcity of food. One of the main reasons animals aggregate during the winter is to keep warm. Some species avoid these harsh conditions by migrating to warmer areas, such as cuckoos in the UK overwintering in central Africa. Others grow insulating coats (like mountain hares in the Scottish highlands), or develop a thick layer of blubber (grey seals and harbour porpoises for example) to keep the cold at bay. But some animals come together instead. Brandt’s voles inhabit the grasslands and steppe of inner Mongolia, where winter temperatures drop as low as -30 °C and strong winds and blizzards are frequent. Brandt’s …