I think you're right. A lot of birds shifted south. But there is a lot that stuck it out. A lot of birds are lacking fat for nesting, and don't want to waste extra energy. They've had pressure all the way up, so I assume a lot are trying to find some rest in the areas they migrated into. Due to the confirmed reports in SD, IA, IL and NE...we should see a constant strings of flocks for a good two weeks due to the spread. I'm hoping that the freeze up doesn't pile all of them in certain areas.
That is my optimistic guess and nothing more. The snow we're receiving could help on predicting a snow line. Keep posted and we'll know before they get here.