In the comments of
my post on wood ducks, there was some interest expressed in the fact that wood ducks nest in cavities, including nest boxes. If you live near the proper
wood duck habitat and are interested in building one of your own, you can find simple instructions for building a wood duck nest box at the
Northern Prairie Wildlife Research Center. The figure below comes from their directions page. Note that it will probably be too late for this breeding season, but there is plenty of time to have one ready for next year.

Additional materials can be found
here and
here.
The final product should look like this photograph from the
Wood Duck Society, which also offers directions for
building a nest box.