My ducks usually are waiting in their house to be locked up at night. If they are not, then usually it's because there is something they don't like about it. Once I used pine needles instead of pine shavings (I ran out of shavings but had plenty of long needles from the trees) and they knew that was different and wouldn't go in. One night it was because there was a dead rat under their house (ugh). If they are not in it, I start looking for a reason why. It has to be a place where they feel safe but not claustrophobic. Does your duck house have windows? Most animals will not go into a dark place because there might be a predator in there waiting to eat them. Sometimes it's hard to know what they are thinking but usually there is SOME reason (in their little pea brains) that whatever housing you are offering is not acceptable or preferable to the outside.
