years ago when i was still living with the parents we had a mouse in the garage. didn't know.
over time i had bits of black foam appearing by my car (MX-5) and no idea where it come from.
then one day when cleaning the car (the engine bay, it was a modified example so regular shows) noticed some wires were missing the plastic outer.
anyhow, found the nest after winter (full of plastic bag shreds and bird food).
and when i had a new fuel filter fitted (due to new turbo installation) we found a second nest, full of bird food, plastic, but no animal.
also for the poison, best to avoid, as if they at enough then rodents will move away from the next to die, so could be in another inaccessible ares of ceiling, in the wall void....