The Alcyon Bird Home from Byer of Maine features a 1 1/8-inch opening, which is an ideal size for small cavity nesters. The deep egg shaped design offers ample protection from predators, and a small whole in the base of the home provides security from weather conditions. An easily removable screw-off cap located on the bottom of the homes allows backyard bird enthusiasts to quickly clean out the empty homes at the end of the season.