when the temperature drops if there are other bats in the area looking for somewhere to hibernate,or,they will continue to use the bird box through the winter. Why not put one up now and give them time to get used to it? You may as well stick up another box for the sparrows just in case you get an increase in bat numbers Dave Bats wont hibernate in the bird box, or standard bat boxes as they are not thick enough and do not offer a stable temperature throughout the winter. Its likely that bats would perish over the winter in one. They are more likely to move into an old building, mine, cellar, cave etc depending n the species of course. They are likely to return next year if the habitat remains similar. Adding a bat box would be a good idea especially for use as a transitional roost, male roost or even a maturnity roost. Its unlikely that its the bats that are putting the sparrows off, sparrows are quite aggressive and would most likely turf the bats out. Bats tend to avoid roosting in or around birds nests and there is documented evidence that birds will occassionally kill bats in these situations (i.e. great tit). Have you been and seen these bats? in my experience most species dont often use bird boxes as they are quite open and dont provide small gaps to crawl into, however species such as daubentons will use them. Do you know what