Greetings, all.
The other day, Thurs., Nov. 15, 2018, I saw this White-crowned Sparrow at Waneka Lake, Boulder County:
Until I put my camera to the bird, I was assuming it was going to be a "Gambel's" White-crowned Sparrow (subspecies gambelii) because, according to conventional wisdom, that's the White-crowned Sparrow subspecies that winters here in Colorado.
Several weeks earlier, back on Thurs., Oct. 25, 2018, whilst at the University of Colorado South Campus (the place with the Golden-crowned Sparrow), Boulder County, I saw this White-crowned Sparrow:
Like the Nov. 15 bird, it has dark in the lores (technically, the supraloral feather tract). Note also its honking big pink bill.
Now compare with this bird, Wed., Oct. 31, at Sombrero Marsh, Boulder County:
This bird has only a bit little bit of dark in the lores (supraloral) and a yellowish bill.
Not a one of these, I would say, is perfect for Gambel's White-crowned Sparrow. And these are the only three immature (formative-plumage) White-crowned Sparrows I've photographed this fall.
The late, great Jim Rising, who literally wrote the book on sparrow identification, told me a while back that he figured many, maybe even most, fall-migrant White-crowned Sparrows through eastern Colorado have some dark-lored, nominate, leucophrys genes in them. Especially young birds--because they're more likely to go off the beaten path on migration.
We have come to appreciate in recent years that many eastern Colorado Yellow-rumped Warblers in spring (when relatively easy to ID in the field) are hybrids/intergrades. Maybe we ought to consider the possibility that a lot of our White-crowned Sparrows in fall carry nominate/leucophrys genes?
Could they instead be intergrades involving the other dark-lored population, oriantha, then Mountain White-crowned Sparrow? Could be! But my hunch, based on timing and geography, is that they're more likely derived from the northern/eastern population, leucophrys. And I also conjecture that they're here mostly in autumn. I wonder if they're analogous to Swamp Sparrows, of which we see so many in November--and then they thin out considerably by the time of the Christmas bird counts.
Well, it would be worthwhile, or so I opine, to try to figure this out. I'm thinking the best time to look for these birds is mid-October (after the summer resident Mountain White-crowned Sparrows, oriantha, are gone) until late November or early December. Do they overwinter? Perhaps, but I also wonder if many perish or keep on migrating. (Again, à la Swamp Sparrow.)
I suppose I ought to to show a pic of a formative White-crowned Sparrow that I consider to be a pure Gambel's. Here's one, from Panama Reservoir, Boulder County, Tues., Sept. 26, 2017:
The bill is dull yellow and not particularly large, the lores are pale and blank.
Finally, I would say that the preceding analysis has consequences for how we eBird White-crowned Sparrows in autumn. Just as with Northern Flickers and Yellow-rumped Warblers, I think we need to be careful about assumptions. I'm amazed at how many good-at-first-glance Red-shafted Flickers prove to have some Yellow-shafted phenotype--especially with after-the-fact photo analysis. Same deal with Myrtle and Audubon's Warblers that wind up transmogrifying into intergrades--again, typically with photo analysis.
Ted Floyd
Lafayette, Boulder County
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