re: What do you attribute the migration change to?

Does anyone have any idea what the difference in waste grain on the ground is now versus before the no-till trend began? Any studies?

Would be an interesting read, I'm sure.

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They follow the freeze line and only migrate as far South as they need to get access to food and open water and even if they don't have access to open water, they wait it out. This is evident because we have seen fewer and fewer Mallards making it into LA and AR while MO and IL are now covered up. Then when or if they do get down here if the freeze line dips that far, as soon as it warms up they almost reverse migrate back

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Very interesting to say the least. But it would make sense that a cold-hardy species like the mallard would behave as such. Perhaps the order of factors changes based on the species. Mallards may be driven more by food availability than by weather, whereas teal, gadwall, etc. Are driven more by weather?