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

If you’re at all familiar with your field guide (and I highly suggest you read through it until you are familiar with it—or at least the birds in your area), you might remember that the perching songbirds (Passerines) begin with the Tyrant Flycatchers. (I’d love to know why ornithologists used the descriptor “tyrant”—they seem pretty benign to me!)

Flycatchers have certain characteristics in common. As a rule, the back of their head is squared off, sometimes with an added crest. If you can watch one for a while, it’s likely to sally forth from a fairly exposed perch, nab an inset in mid-air, and return to the same spot. (At least we can see where the flycatcher name comes from.)

Size varies from fairly small (such as Vermilion Flycatchers) to about robin-sized. Included in this group are the Empidonax Flycatchers, probably the most difficult of all North American birds to tell apart, at least by appearance. Thankfully, our bird isn’t one of those.

Many Tyrant Flycatchers, although by no means all, are similar in appearance to this month’s quiz bird. They have yellow on their bellies, varying amounts of white on their throats and chests, a gray head, and often a dark stripe through the eyes. Tails may or may not have white on the edges—either the sides or the tip. Most of these are some sort of kingbird, in the genus Tyrannus, although some are in the genus Myiarchus. We can be fairly certain that our mystery bird is one of these.

The two Myiarchus birds with any yellow are the Ash-throated and Great Crested Flycatchers. Ash-throated is very light in coloration, so we can easily eliminate that one. The Great Crested lacks the white throat of our bird, so can’t be that either. Now on to the kingbirds.

There are four yellow kingbirds: Tropical, Couch’s, Cassin’s, and Western. Neither Tropical nor Couch’s Kingbirds are found in Colorado, but there’s always a first time, so let’s start with them. The distinguishing field marks are incredibly subtle, to the point where they were considered one species for a hundred years, although they can be separated by voice. Compared to the bird pictured above, both have more yellow and less white on the chest, and the dark eye-stripe isn’t as intense. They were highly unlikely in any case, so we can feel pretty confident in eliminating them.

Now for the Cassin’s and Western Kingbirds. Both are possible in Colorado, although the Western is far more common here. They’re relatively easy to tell apart, if you can get a good look. The Western Kingbird has white on the outer tail feathers, and a white throat and chest. Cassin’s Kingbird has white on the tail, but it’s on the bottom edge, not the sides. It has a darker gray head and chest, with a well-defined white throat.

How about our bird? We can’t see the other side of the tail feathers, but the throat and chest are clearly visible. Yup, it’s a common but beautiful Western Kingbird.

Here’s a picture of a Cassin’s Kingbird, so you can compare. Note the gray chest and small, distinct white chin. Even without seeing the definitive tail, you can see the difference.