[EBB Sightings] When is a pigeon not a pigeon?

Yesterday - setting up for the city fireworks show at the Hercules water 
treatment plant - I spent several minutes watching a bird shaped like a 
pigeon but acting like a swallow, or maybe a small hawk. It cruised back 
and forth over a reedy inlet like it was looking for something in 
particular, occasionally dropping down to the surface (land or water I'm 
not sure; it went behind the tops of the reeds momentarily) and then 
rising again to continue its odd searching behavior.

Further, the coloring was both elegant and weird: vivid black and white 
all over, with vertical bars in the tail (as from alternating pairs or 
trios of flight feathers), pure white wing primaries and secondaries, 
black shoulders and body, and white mask.

If it was a pigeon, what was it doing? Has anyone seen the like?
If it wasn't a pigeon, what could it have been?

-- 
- Hilary Powers - hilary at powersedit.com - Oakland CA -
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