Book 31, Question 123
Why do some birds attack their own reflection?
In the spring, birds like robins and cardinals defend their patch of land from rival birds.
When one sees its reflection in a window, mirror, or shiny car, it thinks another bird has arrived. So it flaps and pecks at the glass, trying to chase it away. The reflection never leaves, so the bird keeps trying. Covering the shiny spot for a few weeks usually stops the behavior.