It is time to do some spring cleaning in your nest boxes. Open them up and remove any old nesting material. Bluebirds are seriously investigating nesting sites right now. I don't expect nesting activity to start until the beginning of April (possibly the end of March), so now is the time to get things ready and aired out.
When I checked Mariton's nest boxes, I found that several had been used by mice over the winter. The photo is of an abandoned mouse nest made of milkweed seeds. After removing the nesting material, I left the boxes open to air . Next week when I monitor, I will close the doors and the nest boxes will be all fresh and ready for feathered residents.