It may seem a bit strange, but different species of songbirds want their house mounted within certain parameters. If the chickadee house is too low, or if the House Wren house is too high those birds will probably ignore the house. There is some flexibility, but if you go to the trouble of building a house for a specific specie of songbird, then it makes sense to mount it at a height preferred by that particular bird.
Blue bird -- 5 to 10 feet
Chickadee -- 6 to 15 feet
House finch -- 8 to 12 feet
Nuthatch -- 12 to 20 feet
House wren -- 6 to 10 feet
Starling -- 10 to 25 feet
Titmouse -- 6 to 15 feet
