I know coyotes take some groundhogs, but I too don't blame them for the overall decline in population. Several things, like mentioned above. Field after field that was once pasture for cattle farmers are now standing with cash crops, and the beef market has declined to the point where crops in fields is a much better investment. So there is hogs there, but they can't be seen in the crops. Still not as many as years past.
In our area, (grey-bruce) all you have to do is take a drive in the country, and look in the trees and on the hydro poles. There is a Hawk, eagle, owl, sitting on what seems like every other hydro pole. Every one of them scouring the fields looking for their next meal. I blame them on the massive drop in jack rabbits as well.
That's my 2 cents