Cabelas Trophy Bucks

there are 5 small varmint that you will find throughout the campaign. all of them will be the actual mission, but a couple are secondary missions which will always be 5 star. here are the varmint you need and on what level they first appear.

marmot 8
rabbit 34
grey squirrel 39
prairie dog 55
ground hog 82

Unlocked for me at beginning of second mission in Minnesota on career play... I used a with scope, and in the far distance you can see some light colored groundhogs. The achievement popped after shooting the first one. Minnesota seems to be one of the latest levels on the game so perhaps you have to pass all of the small varmint hunts.