Bob,
From the information I have read about the lack of groundhogs, everyone always seems to mention an increase in coyote sightings. In my neck of the woods, S/E Pa., I have only saw one coyote in this area. It was a large female and she was actually doing the same thing a friend and I were doing at the time, "hunting groundhogs".
Her hunt was cut short though when my buddy sent a 70gr. Ballistic tip her way.
The post about the ground squirrels was from Miss Stana, mentioning the amount her husband and daughter shot in a year. I believe they are about the approximate size of a gray squirrel or possibly a little smaller, but I am not totally sure. Maybe someone else can better answer your question for you.
13,000 in a year sure sounds like a lot of fun though, doesn't it!
Alan