Shooting from the roof of your car is only allowed if on private property where public access is prohibited. However, you may not take any bird or mammal from a motor vehicle (California Code of Regulations, Title 14, Section 251). Remember, the definition of take includes any attempt to take, such as shooting at the bird or mammal. Therefore, the only shooting allowed would be target shooting. Otherwise, a loaded gun is not allowed in or on a vehicle driving or parked on or along a road or other way open to the public (Fish and Game Code, Section 2006).