re: What do you attribute the migration change to?

One thing that hasn't been said is hot water discharging power plants and factories. This is easily top 3 and maybe 1 or 2. They keep open water, combine that with no-til farming and birds have no reason to leave unless there is a long hard freeze.

My grandfather's club in central Illinois is between the Illinois river and around 10,000 acres of Chicago MSD land (metro sewer division) that does not allow any hunting but is farmed. There is a power plant along the Chicago river. When it gets cold the birds fly between the power plant open water and MSD unhunted no-til land. This has ruined southern Illinois goose hunting almost completely. But there are similar situations like this all up and down th fly-way. Birds have no reason to fly further south when they have food from no-til and open water.