[EBB Sightings] Yellow headed sparrow?

hi folks,

We were at the Hayward Shoreline Interpretive center today (Mon. March 8th) and there was an odd sparrow in the pickle weed next to the center.
He was around the pond and levee on the east side of the building.

It mostly looked to us like a Song Sparrow who had it's head dipped in yellow.
Call was similar but different to the Song Sparrow.

Of course our first thought was Savannah Sparrow - and that may be correct - but I've never seen one with this much yellow.
And there were other Savannah Sparrows around that looked more normal to us.

The bird was basically dark brown stripes on brown/tan body.
Short tail.
Definitely a sparrow beak.
Dropped down into the pickle weed or flew away a short distance if approached too closely.
Yet it flew to within 6 feet of me (into a small bush) when I was standing still.
Small brown (not black) breast spot.
Streaking on chest stopped abruptly mid belly (reminding me of a Lincolns Sparrow).
Head was same, tan with darker brown streaks on face and head.
Top of head seemed to be a wider brown stripe.
Was similar to the juvenile Savannah Sparrow in Nat. Geo. book.

But then it gets weird.
Not just the lores were yellow, the cheeks, top of head, sides of head, under chin part way down it's neck (not sure about the back of the head).
Almost as if you had dunked the entire head in yellow.

We thought maybe it was pollen covered but never saw the pollen covered head look that yellow.
The yellow reminded me of a Yellow Warblers yellow color.
And there was no obvious source of so much pollen anywhere around there.

Any ideas?

We may go back and try to get a picture tomorrow or next day, weather permitting.
I hope it wasn't something very rare blown in by the storm and gone tomorrow.

-Chris & Cyndie
San Jose, CA