We knew that something, probably a flying squirrel, was on the bird feeder. I turned out the lights, pulled up the curtain, and shot blind. Four flying squirrels! I wonder where they hide during the daylight when the red squirrels are eating at this "squirrel proof feeder."
I've taken dozens of pictures of these guys on two different feederes, but I always get their back sides. I think that they have very sensitive eyes and turn away from the light. Any light. Because I have the house all dark except for a nightlight in the next room.