One animal of the North American Desert that avoids the grim surface conditions by living below the desert is the spink. It has long since given up flying. Instead, its wings have become adapted to digging. One the underside of each wing, the feathers have become horny scales, forming an abrasive surface. The articulation of the spink's forelimbs has also changed radically. Instead of flapping in time as birds normally do, the front limbs move independently, shoveling away at the earth. The spink crawls in much the same way as it digs, levering itself forward with its elbows, its weight supported by horny pads at the joints.