[EBB Sightings] Wildcat Canyon Northern Flicker hybrid

Not sure how unusual it is in the east bay, but it was a highlight for us...

At the start of a long hike today in Wildcat Canyon Park  my wife and
I spotted a hybrid (red-shafted x yellow-shafted) Northern Flicker. 
We've only seen red-shafted there before, but this bird had the red
nape spot, the black moustachial stripe and (partially) yellow tail
feathers of the yellow-shafted, which is what we were convinced it was
... until it flew off: the underwings were distinctly orangy-red
however.  Lovely bird that punctuated a day full of the "usual
suspects".  Location was in the eucalyptus trees just past (and to the
right of) the Alvarado picnic area.  Are these hybrids fairly common
(and we've just never seen one despite walking up there a couple times
a week)?

Last week at Layfayette Reservoir a White-throated Sparrow
(tan-striped) was kind enough to make an leisurely appearance as well.
 Although they seem to be popping in at everyone else's this year, our
feeders (in Richmond) haven't drawn a single one this year -- had two
visits last winter though.

Kevin L.