I don't know about any mercury connection, but spoonies, a.k.a. Hollywood Mallards are plentiful this year in the Pacific Flyway. In fact, if you go to your 2011 USFWS survey of bird counts you will find that the Northern Shoveler population in this flyway has spiked year over year (2011 vs. 2010) and is significantly over long-term averages as well. I went down to the Klamath Basin over Thanksgiving and hunted one day. Of the four birds I shot, three were spoonies. I made them into ducky hors d'oeurves, cutting them in chunks and soaking them in olive oil, and fresh chopped garlic. Each chunk was wrapped with bacon and skewered, then cooked over the grill. Eat them with a dipping sauce once cooked. I submit that you can mix spoonie breasts in with your other ducks and not tell the difference. I have never bought into the line that they are a trash duck. To me, that term means mergansers and fish ducks.
Spoonies will fly on bluebird days and will respond to the hail call and decoy so well that you think you are Phil Robertson out there.
When I lived in NoCal and it was a still, warm bluebird day you would shoot your one bull sprig and complete your days shooting with a brace of shovelers...if you were into it.