Armadillos make holes in my yard like that. I wake up at night and snipe their asses...

 

I've had a skunk up to similar mischief

 

A bit hard to tell from the photos, but I think these holes are too small for armadillos, and they don't have the dirt "spray" created when an armadillo digs the dirt out. Based on the apparent size and structure of the holes, my guess would be chipmunk or ground squirrel.

 

I actually have the same issues in my front lawn. Maybe a cat? Or squirrel.

 

Could be something after insects or grubs. Remove the food by killing the insects/grubs and the problem could go away. Of course it could be squirrels after nuts.

 

The reason why I don't think it's armadillos is because they generally create larger holes, and there is a visible spray of dirt around the hole. I also think that they don't dig straight down into the ground, but at an angle (otherwise the dirt that is ejected would go straight back down into the hole). Notice how the one in this video kicks out the dirt.

 

Its a skunk or Opossum after grubs

 

squirrels dig everywhere in my backyard... they bury their nuts...