help holes

I have loads of holes and tunnels appearing all over my new raised garden, i would say they are around an inch wide.. At first i thought mice, but i havent seen any droppings

then today i found this dead and thought i had caught the reason for the holes even though there wasn't any earth mounds only holes



but now i don't think he is the cause as tonight i have a planter that is nearly a foot and half high and sits on the patio, i don't believe any mole could get in there and low and behold i found a hole in the soil.. must be either mice or rats

what are peoples thoughts? what would they be after as i have no food source only the new soil i have put down last year