Serious bird house people know that many design criteria must be incorporated into a well functioning bird house. They include: the size of the whole, the distance between the entrance hole and the bottom of the nest, the ability to easily clean out the bird house, and proper ventilation. The Humphreys include all of these attributes and more. Humphrey Sr. is sized for Tree Swallows and Blue Birds, while Jr. is more appropriate for Chickadees and Wrens. They both have full side opening doors for cleaning and monitoring. Made of Northern white Cedar and Alder they will weather to a silver gray over time.