As for the decreased numbers in pheasants and rabbits I wouldn't contribute the majority of decline to predators. Yes, when you stock pheasants alot will get taken by foxes and hawks. That's mostly due to the fact that they are too dumb to realize that they can't sit in the open in the middle of the day.
I would tend to agree. There have always been hawks, owls, etc... out there even during the "good old days". Sure, there might be a higher number now since they are federally protected but I would have a hard time believing they were solely responsible or even primarily responsible for the decrease in the pheasant population. Habitat loss is what I have always heard offered as the primary excuse..whether due to new farming practices or those $500,000 a home new developments.
On a related note, owls always seem to get the pheasants at our local club when we stock them the night before.