Man, very simlar nest in my car. My car was in a barn for 2 years and they do make a mess of things. I knew they were in the cowl area (Of the many places they made a nest!) because when I looked at the placed where the vent air comes out under the dash, I found debris and mouse poop there.
The reason I was looking for the mouse nests is because I found bits of paper under the drivers seat. It turns out it was part of my buildsheet! Found 1/3 of one. Then I looked and found about 3/4 of another behind the upper rear seat.
Unfortuanately the damage the mice did was bad. Because of the debris in the cowl area and in the drain hole for the cowl area, that caused water to go down the vent hole into the interior of the car as the whole cowl area would fill with water. When I got the car the front rugs basically desintegrated when I tugged on them and the whole car smelled of mouse urine.
My brother in law wouldn't even get in the car. Leave it to the previous owner, a guy that races Mustangs, to just leave the car in a barn unprotected from mice and then park it outside so there's over an inch of water on the front floor boards.
The damage: cowl rot which is visible from under the hood to the right of the master cylinder, hole in floor board.
Locations for mouse nests in my car (maybe yours too!):
-cowl
-fresh air vents
-glovebox
-inside driver's and passenger's door
-inside rear seat upper portion
-under rear seat
-trunk, on the insides or the rear quarters where stuff rolls and is never found again
-behind rear interior panels, where rear window crank assemblies are
-headliner
-air filter housing
-above rear wheel wells
It took a lot of vacuuming with the shop vac....
When I worked at an Acura dealership a customer came in complaining of poor acceleration. When I drove it, it felt like the engine was suffocated. I took off the air filter cover and cat food came spilling out! There was littlerally 2-3 pounds of food in the airfilter and the fresh air intake. We later found the critter as it was torn in half from getting stuck in the rear brake caliper!