Maybe it's time to check your cabin pollen filter?

Probably the same way that mice do, which is to crawl into the ventilation holes under the cowl assembly where the windshield wiper motor is located.

I just replaced the cabin air filter in my Highlander Hybrid and was dismayed to find lots of pink insulation and other debris in the filter. Apparently a mouse had made its way there. The good news was there was no evidence of mouse droppings or fluids, I hope it made it's way out of the vehicle.