I work just across the river from downtown Sacramento, California.  Almost every day around noon, year-round, I see from my window a group of about eight or nine birds fly from Tower Bridge into West Sacramento and eventually back to the bridge.  The bridge is lousy with pigeons and these birds look quite pigeon-like, but there are a couple of things that confuse me.  The first is that these birds are all white.  Blindingly white.  They might have a different color bill, but as far as I can tell