tp20uk said:Oh - maybe I won't buy one after all!
You're right that they are like starling boxes but there usually full of something. Sometimes polystyrene or other times it might be balsa wood or compacted wood shavings. This means that they can make their own hole, but its easier going.
I've always thought that polystyrene can't be a good idea, as you'll end up with those little polystyrene 'bits' everywhere!
I don't know how willing the birds are to use these boxes, and probably would agree that they would prefer a real dead tree.