Great Crested Flycatcher 

The pair have returned this year to again use the nesting box we set up intended for a Wood duck couple.  They apparently like the extra room!  Per iBird Pro, although both parents will inspect potential sites, building of the nest is done almost entirely by the female, while the male closely guards its mate.  Cavities that are large enough in size and opening are the preferred nesting sites, whether naturally occurring or excavated by other species as well as use nesting boxes and other man-made structures.