Thanks for your link paddywack.
Some folks must have thought I was a bit simple asking such a basic question about nature but I feed the birds in our garden and as we have nest boxes too I wondered why they don't use the sensible option and shelter out of the wind and rain.
Your link does help to explain that some birds are sensible and make use of boxes etc.
it was an interesting question carriesmum, and something I'd often thought about myself but never bothered researching it's made me think seriously about resiting the two boxes we've got in the garden when the weather picks up. Did you notice the bit about the 61 wrens in one box? It's hard to imagine isn't it.
Often they roost in hedgerows or ir plants like ivy.
I remember seeing absolutely loads of birds going into bushes in a courtyard at dusk when I was visiting my mum in hospital. There were hundreds of them and obviously the place was warm and sheltered