Quiz 48: Mystery Bird

This bird was photographed in North America, and it’s not some exotic vagrant.

Strikingly patterned, but what is it?

Question 1
What species is this?
Yellow-rumped Warbler
Too much black on the throat, white on the auriculars, no white on the lores, etc. Think molt.
Chestnut-sided Warbler
The face pattern suggests Chestnut-sided, but that species would have chestnut and white on the flanks, yellow crown, etc. Think transitional plumage during molt.
A hybrid
That's what I thought at first, but no, it's not a hybrid. The odd plumage pattern is explained by molt.
Magnolia Warbler
Magnolia would show yellow on the throat and center of the belly, black streaks below, white eyebrow, etc. This bird is molting from one plumage to another.
American Redstart
Question 1 Explanation: 
Here is another photo from the side (click to enlarge): https://picasaweb.google.com/lbogarad/CanadianMysteryBird?authkey=Gv1sRgCIr83ejKwsPBxQE

Photos by Len Bogarad, used by permission. This bird was photographed Jul 15, 2012, on Campobello Island, NB.

I confess that when I first looked at these photos I was convinced this must be a hybrid. It wasn't until about 24 hours later that the idea of American Redstart came to me. Everything fits a one-year-old male Redstart in transition from the brown-backed, yellow-sided immature male plumage to the black and orange adult male plumage.

If it had even a single tail feather the ID would be obvious, but it's a great example of the kinds of challenges that crop up this time of year while birds are molting.

There is 1 question to complete.

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