Did you ever wonder whether you were seeing a Hairy Woodpecker or a Downy Woodpecker? This comparison should give you the clues. The larger Hairy Woodpecker is on the left. Notice the large difference in size (About 3 inches more in length) and in the size of the bills with the Hairy's much longer and thicker. The clue is the Downy's bill is much shorter than the diameter of the head and the Hairy's bill is almost as long or longer than that diameter. Both birds shown here are females. In the male, both will have red spots on the back of the head. This composite photo shows both birds in a true size comparison as the photos were taken from the same distance, perspective and magnification within a 60 second time frame
Below: Female Downy.