Experimentation = Experience
Traditionally, the rule of thumb regarding decoys was simply to increase the number of blocks as the season progresses. The problem with this theory is the birds have learned about this through repetition. Instead, throw them a curve and use a dozen of your best-looking decoys set in an ultra-realistic pattern. Remember, too, the late season usually coincides with a peak in many species' breeding cycles. You might want to be sure that eight of those 12 mallard decoys are hens.
Two final notes about late-season decoy spreads. Realism, as I've mentioned, is paramount now, and there's nothing more realistic than movement. Certainly, that modern marvel, the spinning wing decoy, can add that movement; however, in those states where they're legal, everybody and his brother has one. My recommendation? A jerk-cord. Jerk cords can be extremely effective tools for the late-season gunner, and one which, due to the influx of battery-powered motion-makers, the birds haven't seen every day.
And finally, The Coot Rig. I've put together a spread of two dozen Greenhead Gear coots, and won't hesitate to use those alone. When running a coot spread, I'll do two things. First, I'll set three or four magnum mallard decoys, widely spaced, downwind of the coot decoys. And secondly, I use an all-black decoy in my jerk cord. Coots are constantly in motion, and a bobbing coot in the spread not only imparts motion, but looks natural.
Calling in the Cold
A mediocre caller myself, I can hang during the early season; however, I'll make some changes as the season winds down. First, if I'm hunting with a good caller, I'll let him call. Secondly, I'll use a mallard hen call very sparingly, and even then only as an attention getter. Once I have the birds' attention, I'll change to something other than a hen mallard – Phil Robertson's drake mallard and his Pintail/Widgeon being two of my favorites. These soft subtle calls, when combined with a jerk cord, can make the difference.
Late season waterfowling can be frustrating. The birds are educated, the weather's often less than perfect, and you're at your wit's end as to what to do. Well, folks, it's really no secret as to what to do with these birds on ice – Do Something Different.