I live way down in southern Florida, and the birds were alot slower than last year. It wasn't until way late in December that we started to see lots of birds, but no where near the numbers of last year.
Just chaulked it up to the warm weather up north. Besides, all you northerners need some warm weather once in awhile.
I did notice that while I was hunting up in Indiana this year that the locals stated the same thing you're talking about. Although I saw birds every day while I was deer hunting. Switched to ducks and couldn't find one.