Beekeeping Problem

I wonder if any other beekeepers have had the experience I have had this weekend. I went up to check on the hives after a fortnight of snow and ice. They are WBC hives and I found that on two of them the wooden slides that I put on in the autumn as mouse-guards had been gnawed away in several places to enlarge the apertures. The colonies seem quite OK and on Sunday, a sunny day, they were flying in large numbers. Presumably the gnawing of the slides was the work of freezing or starving mice during the cold spell, but it's astonishing to me that they could have managed it given that the slides are a quarter of an inch thick and solid cedar. The third hive had a metal mouse guard, fitted under the little roof over the landing board, and this had been pulled forward. When I took the top lift off the hive I found that the quilt had been chewed up to make a neat mouse-nest of soft fabric, a bit like a ball of wool. There was no sign of mice, so I suppose they had heard me coming.