I know that many people have posted saying that they have heard birds singing in the middle of the night and I know that the response is usually that birds are getting used to street lighting etc and therefore reckon it is ok to be up at night! However I live in a very remote part of the country, nowhere close to street lighting. I have a glorified shed/lean-to attached to the house and would oftern find my friendly local robins perched in there during the day. However at nighttime I have found a couple of little sparrows in there too. At 11 or 12 at night. Surely it wouldn't be the light in the shed that attracts them? (I have had bats in there before) Do they not suffer by being up so late at night when the temp drops so drastically?
It must be a very welcoming lean-to shivvy, as the sparrows (and bats) are using it as a roost, albeit a temporary one - no light needed, they just know it's shelter.
Even if it appears freezing to us a bird will be glad to rest for the night away from cold winds, rain and low temperatures. It may even save their life as thousands of little birds are lost during cold spells,