For the Allied Precision Solar Water Wiggler (8WW) to work properly, the bird bath will need to have enough water to reach the spinners, which is usually about 1/2" of water. You also need to be sure the water stays at least 1/4" below the plastic bottom of the wiggler. You may need to move the wiggler in your bird bath or place a stable support under it to raise it up to the proper height. Be sure the wiggler is stable enough so it does not fall off any raised support.
