The September Quiz bird (watch the quiz video fullscreen before reading on) turned out to be quite a challenge as the bird never quite managed to satisfactorily show off its field marks in the video.
The first step on a quiz like this is to decide what family it belongs to. At several points in the video we can see the profile of the head and we see a sharp insectivorous bill. This, combined with the overall small size, general elongated shape, and yellowish tint place us in the warblers. One thing that sticks out on this bird is that the face shows both a faint eyeline and weak partial eyering, two features that I think lead to the incorrect ID of Warbling or Philadelphia Vireo.
So, back to warblers. Overall, it is a very drab warbler with some weak yellow color, which may hint at a Tennessee or Orange-crowned Warbler. However if you have a quick eye, you can see that this bird has a nice white wingbar that you can see in the final second of the video as it pops off of its perch. This rules those two species out.
Looking at the slightly yellowish color with white undertail converts leaves you with a group of confusing warblers to deal with, the dreaded Bay-breasted/Blackpoll Warblers, affectionately called the baypolls when we can’t ID them (or don’t want to).
An easy feature to look at to separate these two species is foot color. Bay-breasted Warblers have black legs with black feet, while Blackpolls have black legs (sometimes some yellow) with yellow feet.
Blackpoll Warblers of all ages often show streaking along the sides of the chest while Bay-breasted Warblers do not.
I also use the color of the chest and sides to separate these two species. Immature and female Bay-breasted Warblers stil show a faint bay color along their sides which is usually discernible from the light yellow that Blackpoll Warblers have.
In the video we can see that the feet are light-colored, there is streaking along the sides of the chest and the overall color is yellow, leading to the identification of this bird as a Blackpoll Warbler. Below are two photos I took of the same bird where you can pick out some of these features.