I was forced to take drastic steps after finding the evidence. Mice evidence. Unmistakable mice-in-Papa evidence. Papa is what the FAA wants pilots to say instead of "pee" when talking to air traffic control. Most Piper Comanche N numbers end with a P hence my beloved 1960 Comanche 180 is called Papa around my house. Everyone calls it Papa. My wife hears 'I'm going out to work on Papa," when ever the words don't come.
Recently I was out communing with Papa, who is lucky enough to live nearby at a neighbor's private airstrip. Papa lives in a hangar--an open-front hangar with a slanted floor but nevertheless a hangar. Really it's just a pole barn with siding. The hangar is home to many of God's creatures, none of which respect Papa. The flying creatures sing their songs while balancing on the wires of Papa's VOR antenna, ELT antenna and the nest in the rafters above the fuselage. They poop while they sing.
Mice climb up the landing gear tires and find their way through tiny openings into the soft and comfortable shelter of the cabin. I was surprised one day to find that one mouse--obviously seriously maladjusted--had tried to chew holes in a Travel John Travel John I had accidentally left on the back seat floor after a flight. After use the powder in Travel Johns morphs into  "odorless, spill-proof gel that is non-toxic and safe for disposal in any waste bin," according to the company.
I set about combating this with an idea from the Tips Book of the International Comanche Society Comanche Society to create low-cost metal walls that I now install around each landing gear tire after each flight.
 
Here's the mouse evidence:         
 Mouse problem solved. Bird problem is ongoing. Right now it's just a matter of washing often and well. See you next time