Re: Hybrid White-crowned x White-throated Sparrow?
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Alvaro Jaramillo
Adam I hope it hangs around and molts for you. Part of the evaluation of what features to categorize as important might be age dependent. If you can age it as an adult, vs a youngster, that would be key. White-crowned is not individually variable, just age variation really (restricting to gambelli). Golden-crowned is complex with lots of individual and age related variation during the non-breeding season. White-throated is a true weirdo with age, and then a plumage dichotomy as adults. So how those genes mix and match is one thing, and the age will matter as well in how some of the features are expressed. Good fun. White-throated being a forest bird, and White-crowned being a Taiga bird might be why that hybrid combo is so rare or unrecorded. Golden-crowned takes shrubby habitats closer to forest, and certainly more humid/mesic than White-crowned on average. Although Goldens and White-crowns overlap widely in Alaska and BC. I cannot explain how Goldens come into contact with White-throats, but this does seem more likely than White-crowns and White-throats. BTW, once heard a White-crown in Alaska singing a perfect Golden-crowned song. Birds are weird, that is why we like them. Alvaro
Alvaro Jaramillo www.alvarosadventures.com
From: SFBirds@groups.io <SFBirds@groups.io> On Behalf Of Adam Winer
Sent: Tuesday, September 28, 2021 10:37 PM To: Alvaro Jaramillo <chucao@...> Cc: SF Birds <sfbirds@groups.io> Subject: Re: [SFBirds] Hybrid White-crowned x White-throated Sparrow?
Alvaro,
Thanks for the feedback! And, yeah, gambeli x Golden-crowned was where I started (and may be where I end). If nothing else, a few Golden-crowned had just arrived that morning, making it pretty easy to imagine a Golden-crowned hybrid showing up with the same crowd. It's also a better attested hybrid combo (though there aren't any eBird reports in SF of that combo either). And birdsoftheworld's species accounts make it sound like there's no firm evidence of any White-crowned x White-throated Sparrow hybrid ever having occurred!
What I'll say is that this bird phenotypically matches the things that have previously been called White-crowned x White-throated, and doesn't (to my eye) match the things that have been called White-crowned x Golden-crowned. Specifically, sorting through Macaulay:
... the "WCSPxWTSP" (in the sense of what people have reported as such, not any absolute statement that they are such):
- Show no golden tones to the crown, whereas all "WCSPxGCSP" do (unsurprisingly! the gold in the crown is probably the first clue that they were looking at a hybrid with GCSP) - Have very short and thin postocular stripes, whereas most (but not all) of the "WCSPxGCSP" show postocular stripes that connect to black at the back of the neck - Have fairly thin crown stripes, especially towards the front, with the central white crown stripe coming all the way to the bill, whereas most (but not all) of the "WCSPxGCSP" have fairly broad crown stripes especially towards the bill, with black meeting over the bill.
(I'm not personally noticing any particularly consistent differences between the two buckets in bill or back coloring, though there's clearly variation on both counts.)
I think that the bird in my yard matches each of those characteristics. That doesn't mean, of course, that it *is* a WCSP x WTSP. I may be overvaluing facial pattern, for one; and also how do I know that some of the claimed WCSP x WTSPs aren't actually WCSP x GCSP? (or, ugh, an F2 backcross - we've already established that backcrosses find their way to my yard!)
At any rate, definitely an interesting bird, and it's fun to try to puzzle this through.
Cheers, Adam
On Tue, Sep 28, 2021 at 7:21 PM Alvaro Jaramillo <chucao@...> wrote:
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