A mutt sparrow? (Updated)
Its mother was a White-crowned, its father was a Golden-crowned. Or the other way around. This looks like a mutt sparrow showing the distinctive head markings of both flavors — the black side bands and white stripe of the White-crowned Sparrow and the dab of egg yolk of the Golden. It looks to me like a hybrid. Can that happen? Perhaps a reader with more expertise in this area will weigh in and clarify.
It looks like this question is the core of some controversy among birders. Rusty Scalf, who knows way more about birds than I probably ever will, wrote that this is probably not a hybrid but merely a Golden-crowned Sparrow in full breeding plumage, in other words, hot to trot. There are a couple of web threads on the topic of Golden/White hybrids. An older thread on Flickr shows a number of claimed or hypothesized hybrids, but there is not enough detail of the crown of the birds’ heads to compare them with this little fellow in Cesar Chavez Park. But photographer Mark Schwan (“JuneauRaven”) has a pic on his flickr.com photostream of a bird that looks quite similar to mine, which he claims is a Golden x White hybrid. There is another thread on a forum devoted to bird hybrids, here, with inconclusive photos. The San Francisco Bay Bird Observatory reports what it thinks is a Golden/White hybrid in April 2012, with a photo that has the same yellow/white center streak on the crown. And here’s a 1979 scholarly report on two such hybrids, one found in Michigan, the other in Ontario. The article features very detailed comparative descriptions of bird characteristics, but was done before DNA-based methods were available. I don’t suppose that there’s any definitive way of settling the hybrid question without DNA evidence. 
Thank you for clearing that up! Much appreciated.
Hi Martin,
I followed your link here from your Youtube video, and this also looks like a handsome breeding-plumaged adult golden-crowned to me. All the golden-crowned sparrows I’ve ever handled in the summer have some degree of light grey/white behind the yellow crown patch. Here are a few representative examples from British Columbia:
https://www.dropbox.com/s/1npttim6biyy6a5/crown1.png?dl=0
https://www.dropbox.com/s/w4ydu3nq14vhgna/crown2.png?dl=0
The photos on other blogs and Flickr that you link to, of putative hybrids, all have two clear black stripes on either side of the head, with white/gray in between. Your bird has one big solid black stripe on either side, which is what you’d expect in a golden-crowned.
Hope this helps!
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