Turner's Pond, Milton, Massachusetts, (12/3/2012)
Canon EOS Digital Rebel and EF400 5.6L @ F5.6 1/2000 ISO400 handheld
Update 12/5: They are still present on the 5th and I got to watch them employing an even grander version of the pinwheel feeding tactic. All ten (there are ten now; another must have flown over and popped down to join the flock) Shovelers swam out into deeper water to feed. As they had been doing close to shore they formed quite a tight group and began to feed. Since they were in deeper water they no longer could simply skim the surface of the water to get their food. They were now dipping the whole front half of their bodies under the water as a Mallard or Pintail does to feed. They formed a perfect circle, and employing this tactic, they swam around each other in loose rings as a turning wheel with different layers. They stayed in this spot for about 20 minutes. It was very interesting to watch.
I also observed a group of Mallards (4 or 5 individuals) seemingly emulating the typical "skimming the surface" feeding style of the Shovelers. They were not very good at it and made quite a bit of slurping noise. This makes me think of how I have often seen House Sparrows doing a similar thing; they seem to get ideas from other species and will only try something new if they see another species doing it first (at least in my backyard).
The following link connects to an eBird map of Black-and-white Warbler reports so far this December. Zoom in to North America and you can see most of this guys relatives are literally in Florida right now. See those light purple blocks on Massachusetts? Those are our two birds (the other is in brookline). Zoom in and you can see the individual sightings and the checklists that accompany them. Yup, eBird is awesome.
And the think from the 5th, though not as interesting: