For many years a particular red cardinal male combated my mirror on my car. Fortunately he was not a woodpecker that could have broken my mirror. The cardinal would go into full battle mode with ferocious attacks on my mirror. Due to age he is no more. I found him most amusing he also got scraps of food from our meals. I miss him.
Maybe he’s responding to his reflection thinking it’s another bird...
I’ve seen budgie birds fall in love with their own reflection thinking it was another bird...
We put plastic bags over our side mirrors if they are going to sit outside.