"As the night draws in and you close the front door on the cold winter day, spare a thought for small birds as they embark upon the long chilly night. Some of these birds, such as blue tits, great tits and wrens, seek cavities in which to roost overnight, sometimes huddling together to keep warm. Millions of nest boxes are provided in UK gardens and these might provide an ideal network of ‘bedrooms’ for these birds. Help the British Trust for Ornithology to find out more, and discover the species roosting in your garden, by participating in their Roosting Survey."
Taken from British Trust for Ornithology's Roosting Survey website.