Couple of things that may factor into the stats. One has been mentioned earlier - the storms do not just seem to hurt the habitat, but it also seems to wipe out birds in those areas as well. Hunted a place a couple of years ago where the population really seemed decimated by tornadoes that had come through in late February.
Two... for whatever reason, the population where I've hunted the past three years has declined. I don't know that I can pin it on one factor - but the fact seems undeniable that I have less birds.
