To refresh your memory, here is the photo from September’s Bird Quiz. It was taken in Colorado during the month of September. Don’t read any further if you want one last chance to identify this bird.

What do we see? Yes, it’s a songbird, which eliminates about half the field guide. The top and sides of its breast are bordered with rust-colored feathers, the middle is beige. There are spots below its throat. The dark eye has a white ring around it. The beak is dark and pointy rather than the seed-cracking wedge of sparrows and finches.

Our bird is perched among the branches of a juniper, so we can get an idea of its size—about that of a smallish robin, perhaps. At least it’s bigger than a Bushtit and smaller than a raven.

Since we can’t see the rest of the bird, we have no idea what color the other side of the bird is. We don’t know about wing bars or outer tail feathers, or many of the other frequently used field marks. However, I promise we have enough information for a confident ID. Really.

Let’s start with the spots. Streaks are pretty common on songbirds but spots are not; their presence narrows down the possibilities considerably. Which Passerines have spots? Although the field guide calls them streaks, Pipits could be said to have spots, at least in my opinion. Thrushes have spots. Starlings do too, but this bird looks nothing like a black starling—or a Cactus Wren, another spotty bird! Some thrashers have spots, and so do juvenile mockingbirds. And that’s about it.

A quick look at the beak eliminates the Curve-billed and Bendire’s Thrashers (the ones with spots). Color eliminates the black and white Northern Mockingbird. How about the pipit?

Pipits are brownish and the American Pipit, the most likely to be seen in Colorado, even has a white eye-ring. However, at the time of year this photo was taken, at the end of the summer, a pipit will have molted into its non-breeding plumage. It would be whitish with well-defined dark streaks, not buffy, and definitely not spotted. It’s not a pipit.

That leaves the thrushes. Thrushes also have a white eye-ring, so that’s encouraging. Now comes the tricky part—which thrush is it? Eliminating those without spots, our western field guide lists eight candidates. They include two of the three species of bluebird, a juvenile American Robin (left), a juvenile Townsend’s Solitaire, and the four species in the genus Catharus that are present, at least occasionally, in Colorado: Veery, Swainson’s Thrush, Hermit Thrush, and (rarely) Gray-cheeked.

Happily, the Catharus thrushes and a juvenile robin all have dark spots on a lighter background; black or brown on white in most cases (a Veery’s spots are brown on buff). Our bird has white spots on a pale brown background. Townsend’s Solitaire has white spots, but they’re all over the bird, and against a black background. That leaves the bluebirds.

At this point, you may be thinking bluebird? This doesn’t look anything like a bluebird! Ah, but it does. It looks like a juvenile bluebird!

Like many thrushes, Eastern and Western Bluebirds start out with spots that disappear when they become adults. (Mountain Bluebirds have dark streaks on light gray, rather than spots.) Both birds have rust-red breasts as adults. Seen in September, this bird has in the process of molting, losing its spots and gaining the vibrant rust breast of an adult male. The only spots left were at the top of his breast, just below his neck.

Can we tell the difference between Eastern and Western Bluebirds? Eastern Bluebirds have a white, rather than grayish, belly. They also have their rusty markings extend onto the sides of their neck and up under their chin (to the beak). In Western Bluebirds, the neck is blue. (Here’s a photo of an adult male Western Bluebird, with his all-blue head.)

Since this bird is too young to have all its blue feathers, I, at least, can’t tell which species it is. The odds are in favor of it being a Western Bluebird, since Eastern Bluebirds aren’t often found in Colorado. Additionally, I had the advantage of taking the photo. All the other birds in the area were Westerns. While I can’t be sure, I assume that two of those Westerns were this bird’s parents.

Here’s one more photo of our quiz bird. See? A Western Bluebird.