There are two types of Northern Flicker — the Yellow-shafted, which is considered the eastern species and the Red-shafted which is the eastern one. This difference is determined by the coloring on the underside of the wings.
The only woodpecker that feeds on the ground and the only brown-backed woodpecker. The Yellow-Shafted is the eastern species. The yellow coloring is found on the underneath side of the wing. Their song is similar to the Pileated Woodpecker so you’ll have to listen close to discern between them!