Greg -
Howdy !
For my money... yeah.... the numbers of " Soybeanus Digestus " went into decline co-incidental to the onset of " no - till " farming.
Groundhogs already had to contend w/ the contamination of a lot of their prefered food, by herbicides like Amiben, Lorsban, Bigfoot, Prowl; and the like.
On top of that, no till brought along the practice of " burn down " or chemical treatment of the non cash grain vegetation; which was needed to help the soybeans out-grow any competing plants. Can't say fer sher how much of the soybean growing season groundhogs would be exposed to contaminated beans plants ? But, I point out that many herbicides are called " post -emerge ", or... for application after the young plants emerge from the ground. That co-incides w/ mom emerging from the den w/ her pups, for their introduction to the joys of soybeans.
Heck... read a jug of " Roundup ", and see how long after sprayin something w/ that stuff that you'd eat the treated plant !
Now, add-on that groundhogs are on the coyote " hot lunch program ", predation by hawks and such, foxes, determined dogs, vehicular mischief; et al.
There a many secluded spots in NE Indiana where groundhogs might go years w/o ever being shot at. And even in those spots, groundhog seem to be less prevelant than what had been historically seen. IMHO - yes... they CAN be shot into oblivion. But, that is not the universal or even the leading cause for the decline in numbers.
IF you can find a farmer that grows soybeans purely " organically " and eskews chemicals, you might see whether his groundhog populations seem more robust ? Good luck with that. His combine costs more than your house, and he has lots of other machinery to pay for.
" Rock N' Roll is here to stay " ! So is " No Till ".
With regards,
357Mag