I will tell you I have shot a lot of pheasants around the country. My belief is the birds are perceptively bigger the farther north and west. Now species variation might be at work, or because as you get north, it requires more strength and size to acclimate to the enviorment. I have seen the difference between Kansas Birds and birds from Nebraska 100 miles north. Certainly between Jewell County Kansas birds, and birds in Cherry County, Nebraska. I don't descriminate, I like them all! By the way, species which live in the arctic region, Polar Bears, et.al. are bigger than similar species at more hospitable climates, Same as lower 48 grizzlies or Alaskan Grizzlies, Lower 48 moose versus a Canadian/Alaskan moose. Might be climate that makes a difference, but there was a wide variety of pheasant genetics blended into the stew, who knows what particular combination clicked for a particular area? You find color variation as well between these birds, visual evidence of some variation!