We used to have alot of quail here. See very few anymore. The habitat here has actually improved significantly.
I "suspect" quail may need a much larger amount of contiguous good habitat to thrive over time, than has been previously believed (even without the obvious increase in hawks and other predators). We had much more of this contiguous good habitat prior to the 1960's. Yet, even a place like Ames which has it today, quail are not thriving like they did prior to the 60's. The situation today at Ames alludes to predators being a bigger problem on quail populations than in times past.
In a sense, turkeys are kinda like just big quail, but they seem to have a much greater range (making them less vulnerable to localized habitat problems), and they're large enough to more easily escape many of the predators that can easily take adult quail.
Unlike most other birds, quail live and die a natural life in very close proximity to where they're hatched. If anything goes wrong, all the quail in an area can die off (or be killed), and there are none going to migrate down with the next cold snap up North.