So, we're still trying to figure out the photo quiz that I posted last week.
Here's the quiz.
And, here's the discussion so far.

When the birdwalk group first saw this bird, it was facing away. The blackish cap, contrasting with a grayish head lead me to believe that this was a Gray Catbird, a common shrub-nester in the park. The tail was also cocked at such an angle that it appeared longer than it was, suggesting the long-tailed Catbird.

But, then it stood up, showing that white throat, and we had a better look at the white supercilium – something that a catbird should not show. The pale gray plumage, and the wide-based bill suggested Warbling Vireo, which can appear somewhat capped. However, they usually nest high up in the trees, but they do occur in Royal River Park. Plus, when it shifted again, we realized that the bill was too long for a vireo, and lacking the steeply curved, almost hooked upper mandible. Almost by default, we began to think about a female American Redstart, a bird one birder had just seen fly into that area anyway. Female American Redstarts are very pale gray, but the darkish cap is odd.

Basically, what we have is a bird that is not fitting any species perfectly. Plumage varies. What varies less is the shape of such structures as the bill. The bill is crucial here: we see a straight, chisel-shaped, deep-based bill. It’s fairly long (relative to the head), and come to a rather blunt point, and is solid black (most birds show at least some pale at the base of their bill).

This bill is perfect for an American Redstart, and really it’s just the dark cap that is preventing us from confirming the identification. But, everything else fits, so what we have here is indeed a female American Redstart that happens to have an abnormally dark crown (in closer study later in the day, when I returned to take these pictures, I noticed a few blackish feathers in the otherwise dark gray crown, accentuating this capped appearance.

But, if the glove DOES fit, you CAN’T acquit, so as proof of her identity, here ya go:

OK, it’s a lousy picture, but it shows the yellow splotches on the side of a whitish underbelly, greenish wings (the yellow patches here are not visible) and mantle, and a gray head, neck, and rump of the female American Redstart