Almost every day I hear the thunk of a bird hitting one of our windows. Often I peer outside and spot the injured avian, out cold on the concrete floor of our back porch. I keep the dog inside for a while, and half an hour later, the bird is gone--I assume to fly another day.
Maybe the birds are addled by their own reflections in the sunlit glass. Or maybe it's the same bird each time, its brain turned to mashed potatoes by serial concussions. Or maybe it's just stupidity--after all, they are relatives of T-rex.
Which gives you another theory as to the reason dinosaurs disappeared off the face of the earth.