The Predominately Western, Golden-crowned Sparrow
At first glance you might not recognize this bird as a Golden-crowned Sparrow (Zonotrichia atricapilla). It is an immature bird with an indistinct yellowish forecrown with dark stripes on its crown (click on photos for full sized images).
The entire Golden-crowned Sparrow population migrates within North America between winter and summer ranges…
arriving in California in September and October, often foraging with White-crowned Sparrows. Even though it doesn’t show on the NatureServe range map above, Golden-crowned Sparrow vagrants have been recorded eastward to Ontario and Nova Scotia, Michigan, Massachusetts, Pennsylvania, and New Jersey; also south to Alabama, Texas, Louisiana and Florida1.
Note that even though this is a first winter bird, it has already attained the grayish-brown, unmarked breast and the black and brown streaked back of the adult bird.
This adult Golden-crowned Sparrow is more easily identified in its winter plumage.
and as the winter progresses…
the muted crown pattern of the wintering sparrow…
turns into the very distinctive breeding plumage of the Golden-crowned Sparrow, peaking in April with its bright yellow crown and broad black eyebrows.
Resources: 1Birds of North America Online