Here you can clearly see the DSV fluff and seedpods used by these enterprising mice to build their nest.

Of the 21 nest boxes I have checked so far, three contained squirrel nests, two were complete and one was partially completed. Also in the box with the partial squirrel nest, was a nest made by Polistes dominula with one dead wasp attached. Two of these nests I know were made in the spring, the other one looks well established so may also have been made then. None of the boxes contained house sparrow nests, for the 2nd year in a row. Although I have more boxes to check, the ones in the Old Field have never been used by house sparrows in all the years I've been maintaining them, so I don't expect to find any of their nests when I clean them later.