Dried corn cobs (with or without corn still on them) are
easy to wire together into a box shape, leaving a gap
between two smaller pieces in the front for a
"door". Wire on a thin plywood floor; use more
cobs, or perhaps wood, for the roof. (Though beware:
if the person you’re creating this for is in squirrel
territory, the bird house is likely to become a squirrel
feeder!)
