He is obviously a bit dim, but, he is protecting his territory from the rival he sees in the reflection.Here is a picture of a Chaffinch, we have named him Charlie, for the past two days he has constantly been chasing his reflection in our conservatory windows, we scare him away, for his own good, but he keeps coming back, if he keeps this up he will die of exhaustion.
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Just be thankful its not a woodpecker
due to swallows who nest inside the structure and drop the obvious on top of the car