A few years ago, I vowed to never try to identify downy and hairy woodpeckers again. Each identification I made was wrong and I couldn't seem to remember which was the smaller woodpecker. For some reason, that changed this winter. I created a mnemonic that helped me remember which bird was which. The constant repetition of the mnemonic finally created automatic knowledge. I look at a woodpecker and now I know which it is!
The downy woodpecker is above. It is the smaller bird, which you can see by its relative size as it perches on the suet feeder. The smaller bird also has the shorter beak. Also, look at the tail feathers. There are bands of black there with the rufous feathers filling some bands.
"Smaller" and "shorter" are meaningless without comparison, so we see in the photo below the hairy woodpecker which is larger and has a longer bill. It has no bands on its tail, only the rufous feathers. (However, I have read that some hairy woodpeckers in the northwest of the US have bands of black.)
I have observed that hairy woodpeckers seem to be more aggressive than the downy. Downy woodpeckers have their spats, but the hairy woodpeckers attack each other more often and more violently (but I have not seen any injuries). I also think, but am not certain, that the hairy woodpecker gaze has an intensity, not seen by me in the downy, that you see in this photo. These are my observations and I have not verified then with any research.
What was my mnemonic? D is for downy and H is for hairy. D comes before H in the alphabet, as smaller/shorter comes before larger/longer (on an imaginary continuum). Therefore, the downy is smaller and has the shorter bill. If you have the same problem identifying these birds that I had, I hope this helps! Have fun watching the woodpeckers! I have to go to Flickr now and sort out my downy and hairy woodpeckers!
Flickr: My Downy Woodpecker Set
Flickr: My Hairy Woodpecker Set
Flickr:: My messed up Woodpecker Set