White-crowned Sparrows and Golden-crowned Sparrows inhabit the same set of bushes on the north side of the park, and elsewhere. They’re separate but closely related species. It shouldn’t be a total surprise, then, to find a sparrow that has the markings of a white-crowned and of a golden-crowned. This bird does. The front of its head streak is bright yellow, and about halfway back it becomes bright white. The companion bird shown briefly at the beginning of the video is a pure white-crowned.
I saw a similar bird on the west side of the park three years ago. At the time I consulted a bird expert and did some research and came away persuaded that it was probably a white-gold hybrid, but one couldn’t be sure without looking at the DNA. That’s still where it’s at, as far as I know.
Oops! Just had a comment on the YouTube version of this post from Emily Hudson, who studies Golden-crowned Sparrows for a living. She says this is a normal Golden-crowned adult. “The light gray at the back of the crown is common when they’re in breeding plumage. The dark bill is also pure golden-crowned.” So there you have it.