[EBB Sightings] Odd duck at Point Emery

I had a close look at a duck with a completely white head and a  dark  
gray/black  neck and  back with mottled dark gray  and white flanks.  It 
had a rounded, not pointy, black tail.  My first impression was a winter 
long tailed duck, as it is about the same size (between a ruddy and a 
scaup) and dove a lot. The base of bill appeared bluish in the bright 
light; the tip was dark.  However, I haven't found any photos of long 
tails with completely white heads.  It did not appear to be an eider or 
smew.

Unfortunately, I did not have a camera.

I saw the duck seen  about 11 AM today (hr or so before high tide) on 
the west side of the entrance to Point Emery.*

Point Emery*
Thomas 1997   
p.629  D-5.
Small spit of landfill extending into San Francisco Bay 
north border of Emeryville.
Parking, path, benches, view and birdwatching.
Access from frontage road west of Hwy 80 near Ashby exit.

Harold Newman