Song development in the zebra finch and other estrildid finches

Root crop cleaning apparatus including a pair of adjacent, counterrotating cleaning rolls arranged in root crop receiving relation, one of the rolls being formed by a plurality of resilient disks mounted on a shaft and maintained at equal axial distances by means of smaller diameter spacers interposed between each adjacent pair of resilient disks, and the other roll being formed by a plurality of axially extending rods connected to a shaft at equal radial distances from the shaft and at equal circumferential distances from each other, the resilient disks on the one roll being yieldable axially and cooperable with the axially extending gaps between the rods on the other roll to permit rocks and other foreign objects to pass between the rolls without causing damage to the apparatus.