Re: White-throated Sparrow: White or Tan-Striped?
Stephen T Bird
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On a limb, if I was forced: 1st winter white.
The supercilium is a poor differentiator in basic molt, particularly a late-winter well-sullied adult or 1st winter.
https://sora.unm.edu/sites/default/files/journals/jfo/v060n01/p0073-p0083.pdf Figure 4 (or simplified by Sibley)
The darker lateral stripe & (apparent) lighter median stripe, sharply contrasting throat & gray cheeks, rufous upper wing suggest a 1st winter white morph to me (which also permits the light breast streaking); but thats all the caveats accepted that winter can be difficult.
Once I've accepted that, I spuriously delude myself into thinking "yeah, that supercilium is fairly light for a 1st winter."
Other's thoughts? Don't take my word for it.
There are not intermediates (to my knowledge). The morph is due to a a gene inversion following a chromosome duplication/introgression likely from Harris Sparrows.
Some interesting reading: https://www.audubon.org/news/the-fascinating-and-complicated-sex-lives-white-throated-sparrows
The argument is made, it uniquely has "4 sexes: near-obligate disassortative mating (i.e. a white morph must breed with a tan morph, regardless of each's sex). Almost as interesting as Acorn Woodpecker mating strategies.
On Tue, Mar 9, 2021 at 6:59 AM Sam Zuckerman <samzuckerman@...> wrote: