Even though it sucks, the best thing to probably do is pull the dash out and find the little guy.. But yeah, pull the wiper cowl off and see what ya can fish out..

Mice invaded my 79 over the winter, I found probably 10 live mice in the car.. I had to completely pull the interior out, pressure wash the carpet and so forth. Their urine ate through the undercoating I put in the interior, and actually started to rust the floor pans out.. I bet it took 2 weeks to reverse the damage they did, luckly they didnt eat the wiring harness.. Some days you can still smell a hint of urine in the car, ticks me off, the interior wasnt even a yr old yet. Thats what I get for leaving the wiper cowl off and not messing with the car all winter.

Pulling the dash sounds bad, but after ya do it a few times ya get pretty good at it