At the Caretaker class of Feb 1998 and Nov 2001 instruction was given on the
construction of natural animal shelters, in particular "mouse houses".
The purpose of making mouse houses is to encourage mice and other small animals
to move back into an area that they are no longer present in, or to increase the
populations where shelter is lacking. Of course, they also need cover,
water, and food. But here we are only dealing with shelter.
You may be asking, "Why on Earth would someone want to encourage mice to
inhabit an area?". The answer is simple. Mice are near the bottom of the
food chain. By encouraging mice, you indirectly encourage the predators of mice,
such as foxes, coyotes, owls, raptors, etc. to also inhabit the area.