Mylar may have a metallic film applied to it, but not all Mylar does. Metal is not necessary for the material to be reflective. Mylar is also used as an electrical insulator.
Mylar is coated with a metallic conductive coating. In my County (Kern County California) Mylar balloons are Banned because of the risk of them getting into power lines and starting a fire.
Ive flow DJI drones since 2012 and never once been attacked by birds. I’ve seen vultures frequently, fly around in circles above the drone, I’ve had waterfowl zip past, a little close for comfort, I’ve seen hawks look on in curiosity, sea gulls...