Providing Cover for Birds
Roosting boxes or natural plant covers can also aid birds seeking protection from cold weather.
Shelter is also needed for protection against natural predators, such as birds of prey.
Cats are unnatural predators and birds also need shelter to escape from them.
Be sure to clean out old nests from houses to help reduce the possibility of parasitic bugs surviving the winter.
It also allows birds the opportunity to roost in a clean house.

  Birds only nest during spring and summer—their breeding
 season. But during the rest of the year, cavity-nesting birds
 often use these same boxes for shelter at night, particularly
 in winter.
 You can help your backyard birds keep warm overnight with
 a specially designed roost box.
 Any backyard favorites that typically nest in boxes—
 bluebirds, chickadees, titmice, nuthatches, and small
 woodpeckers—may seek refuge in it.
 
 Roosting boxes differ from nest boxes in several ways.
 A good roost box is designed to prevent the birds' body
 heat from escaping, so, unlike a nest box, it has fewer
 ventilation holes. Also, its entrance hole is near the bottom
 of the box so the rising warmth doesn't escape.

 There is lots of information to be found on the web on how
 to make a winter roosting box.