Over 8 million of these delightful clocks have been purchased since they were first introduced, and here's why: At the top of every hour, an authentic recording of a North American bird song plays, creating a bright spot in any nature-lover's day. Our 20th Anniversary versions are framed in green and stand or hang; light sensor turns songs off after dark. Uses 3 AA batteries (not included). Choose 8" or 13" diameter.