Try to remember it next year. You can open those easily on front, top or bottom (different ways to build them). Then you just take out old nest etc. But it can be bit messy... Birds that do not migrate spend cold winter nights there and there is crap etc. There can also be eggs and sometimes dead chicks so I need to ask someone to take those pictures-don't want to touch camera with those cloves same time cleaning them.
RE: Birds nest boxes ready for summer 2018