The Onyx Clever Clean bird feeders from Droll Yankees feature a twist-off base that allows you to dump chaff or debris each time you fill your feeder. This helps you prevent mold toxins that can be deadly to birds. They also have Comfort Perches, 180 degree two-position rings that allow the birds complete discretion in their orientation to the port. They are available in both Sunflower/Mixed Seed and Nyjer versions.