I knew of a commercial hatchery once that euthanized chick culls by tossing them in an old Igloo cooler along with some CO2 (dry ice) pellets. Suffocating them. PETA would not have approved.
My cats do a number on the 13 stripers out here. Only had one Richardson's ground squirrel, commonly known here as a gopher. Sask boy's pastime, gopher shooting.
I have pocket gophers and chipmunks. Chipmunk is twice the size of a mouse and striped. Both like the engine and passenger compartments of your vehicles. I've tried most everything to repel. What seems to work best - open the hood of your vehicle. They don't seem to like the open spaces. Don't like the engine compartment - probably won't go in the passenger compartment.
Also - pill bottle full of cotton balls. Soak with oil of Peppermint. Put in the glove compartment. If nothing else - makes the passenger compartment smell nice.
Forty plus years out here. One and ONLY one squirrel. A pine squirrel. I put out unsalted peanuts. He liked them but he moved on to other places.