We have a bunch of chicks about a week or so old and both parent birds have been in and out the box feeding them without difficulty. However just recently they appear to have a problem entering the box. The male bird in particular frequently hovers and puts his head into the entrance but that's as far as he gets The female has more success thank goodness but I'm concerned the problem might be down to the wood swelling because of the rain. The box is constructed from 25mm thick hardwood. Appreciate your thoughts