Apparently birds are uber fussy, so our box, with its 32mm hole, is suitable for house sparrows, tree sparrows, and nuthatches only.
Storm only hit my thumb with a hammer once, so I figure I got off pretty lightly! You can find out how to make your own nestbox here.
Dad was really chuffed, and I was really glad to give him a present that should bring happiness to him (and the birds) for many years.
Third secret birthday project coming soon!