If you were to remove the fenders you would find rather large, squarish openings at the ends of the plenum (the channel that the air is drawn into).
These are additional drains, but as the OP has found, critters can climb into the airspace between the front fender and 'A' pillar and make it into the plenum.......their curiosity and search for food often finds them falling down the air inlet (on the far right, opposite the inlet grill) and onto the cabin filter.
Sometimes they get out, sometimes that is their last event..........debris and signs of gnawing obviously mean they figured it out......a stinky body you have to get out of the system means they didn't fare so well.
Good Morning.....think about this, enjoy breakfast, ha ha.
Rob