If you have to hibernate your bike for the winter and you have undetected mice in your garage, they can get into the air-filter area. If you have a borescope, you should be able to see the nest. If you see the nest in the spring, you'll be changing the air filter. If you only do 6000 miles per year and you still have the mouse problem, you'll be changing the filter every 6000 miles.
I'll try my best at keeping mice at bay, but a borescope seems like the only way to know if your filter provided a winter home.....unless you want to spend the hours removing pieces to eye-ball it yourself.