posted August 16th, 2012; last edited August 20th, 2012 –– David Sibley

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?
A
Chestnut-sided Warbler
Hint:
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.
B
A hybrid
Hint:
That's what I thought at first, but no, it's not a hybrid. The odd plumage pattern is explained by molt.
C
Yellow-rumped Warbler
Hint:
Too much black on the throat, white on the auriculars, no white on the lores, etc. Think molt.
D
American Redstart
E
Magnolia Warbler
Hint:
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.
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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