I have both Downy and Hairy woodpeckers at my suet feeders. They are not always easily distinguished. Many birders rely on size or the length of the bill. (Downys are about 72% the size of Hairys). However, if the woodpecker is high up in a tree or at some distance, size may be hard to gauge, and you may not be able to see the bill clearly. Another way to distinguish these two species is by the feather pattern on the back of their heads. Downys have a black cap below which is a white band that completely rings the back of the head and then a black band that completely rings the back of the head. Look closely at the photo and note the white ring is nearly continuous on the bird’s head–this is a female Downy (males will have red feathers on the back of the head instead of white, but the red will also be continuous in a ring below the black cap).