Hairy or Downy Woodpecker?
Most field guides will not tell you how common the bird is. That is especially important for this pair because downies outnumber hairies at least eight to one in backyards. Hairy Woodpeckers prefer older woodlands that you won't find in a lot of suburban areas. The only time that it would be even reasonable to identify a hairy is during migration. When food supply starts to run low, it becomes plausible for a hairy to stop at your feeder. Chances are, if you see a woodpecker that looks like the above picture on the left, it is a Downy Woodpecker.
However, if you happen to be birding in an older forest and you come across this dilemma, there is a way to tell the difference. The most obvious field mark to look for is size. The Hairy woodpecker is 30% larger than the downy. I heard someone once say, "Downy is dinky, and Hairy is huge." If you have to question the size or get a closer look, it is most likely a downy. As stated in the above quote, the Hairy is huge. That is not an understatement. If you are close enough, you will know it's a hairy.
If there is such a rare time that you cannot identify this mysterious creature by size alone, there are other field marks to help. The second most obvious marking is the bill size. The Downy Woodpecker has an abnormally small bill. It looks as if it couldn't even make a dent in a twig. On the other hand, the hairy has an extremely long bill. It is described to be as long as the head from front to back. Once you are familiar with both birds, the bill size is almost as obvious as the body size.
In addition to body and bill size, there are other field marks that can help but can only be seen up close. For instance, the white under tail feathers on the Downy have a few horizontal black bars while the Hairy does not. If you are not an experienced birder, the songs are too similar to tell apart. Using these tips, you can now successfully identify the difference between the Hairy and Downy Woodpecker. All you need to remember is "Downy is dinky, and Hairy is huge" and you might never need to reference your field guide for this bird again.