Mystery birds are fun to investigate because they force us to look at the clues that are given us, even if the clues are few and far between. We don't always get a good clear view of a bird so often we have to identify the bird with whatever tidbits of information were provided.
Like this mystery bird. All that's there is a head and a half belly of a medium-sized bird on a tree. We quickly liken the red cap to birds we know well, like a male Hairy or Downy Woodpecker. But we can rule them out, including the juveniles, because of the patterning on the belly. Hairies and downies of all ages have a clear white belly. After breeding and before molting, adults may have a worn, dirty belly, but not patterned feathers.
We often rely too much on colors but this mystery bird gives us another clue: posture. This is a clinging bird, one that is able to hang on the side of a tree. Not all birds can do this. American Robins and other thrushes typically don't, Gray Catbirds don't, flycatchers typically not, and so on, ruling out many medium-sized birds. And even if we've never seen our mystery bird before in our life, we do recognize that its posture is like the woodpeckers that do frequently visit our yards and trees.
With that clue in hand, we have a starting point - we start our search in the woodpecker section of our bird guide. Knowing where the bird was seen is important - we shouldn't waste too much time trying to turn this upstate New York bird into a Ladder-backed Woodpecker which is only found in Texas, the southwest states and Mexico. Sure, birds have wings and birds are sometimes found outside their range, but we should start with the most likely birds and venture into rarities only if we rule out the likelies.
My particular eastern bird guide shows 12 birds in the woodpecker family. We've ruled out hairy, downy, and can quickly rule out another 3 far out of range, and of course it's not a Pileated Woodpecker of any age. So we're left with 6 possibilities. The speckly head just doesn't look like the clear head of a Red-bellied Woodpecker or Northern Flicker, and flickers, though they can cling, are most often seen on the ground. And we can rule out American Three-toed Woodpecker and Black-backed Woodpecker because of the red on the head, plus as birds of the boreal forest, these two species are very unlikely in our area. Again, stick with the most likely birds to be seen.
So we're left with Red-headed Woodpecker and Yellow-bellied Sapsucker. Because of the time of year - September - we know we might be dealing with a juvenile bird wearing very different plumage than the adult bird. It's clearly not a red-headed adult, but the red-headed juvenile doesn't have that namesake striking red head. But it's pretty uncommon. We've got to more strongly consider what's more common. Which leaves us with Yellow-bellied Sapsucker. Even looking at field guides without images of the juvenile, we can pretty safely arrive at this conclusion, but if your guide shows it, like my Stokes Field Guide, all the better!
As a juvenile, it will keep this plumage into the winter. They're very uncommon for us in winter, but even when a juvenile like this returns next spring, it still might not have full adult plumage.
I hope this little post demonstrates that we don't have to throw our hands up in frustration when we get a poor view of a bird. There are always SOME clues! We can take those "lemon" looks and use what we DO have to make "lemonade"!