Going Postal

We have a post lamp in our front yard. For years we had a green light therein on a photosensitive switch. It came on at night and went off at dawn. The bulb died a month ago, and I replaced it. The new light bulb is just a drab boring white light. Today, Dr. P noticed that the top of the shade was hanging loose. He texted me on his way to work. I went to look headed to work. The two screws which held the cap in place are gone. You can kinda see in the pic the little nub which is where they attach on each side. Who would take our screws? Would a critter have been able to unscrew two fasteners? Why would a critter want to get inside a light fixture? It’s difficult to tell if the screws fell because there is a foot of snow on the ground. So weird.