I'm interested in this topic as well. A guide told me last year the flyaway in N.TX has shifted west over the past 10-15 years. All the development along the 75 corridor has eliminate agricultural land the birds would use between the major reservoirs on that side of the metroplex. He thinks the bigger numbers now don't come east of 35W. I haven't been hunting this area for all those years so I'm interested to hear if others agree.
I think that a guide is a goof.
There has always been more birds out west then east. Nothing has shifted east to west only thing that's happened is the mallards stay further north.