Cardinal male attacking his reflection in a parked car mirror. We frequently get asked this time of year "why is the cardinal pecking at my window, or mirror". Birds do not know about reflections so, for a bird defending its territory, it sees its reflection and thinks it is another of its species attacking back. This is not a good thing. The bird wastes energy and could potentially mildly hurt itself. The way to prevent it is to remove the reflection from the birds viewpoint and cover the outside of the window with screening, cloth, or something, or in the case of a car mirror, a paper bag or cloth, or move the car. Once breeding is well underway, a birds territorial defense will wane and this behavior will diminish.