[HesterF]

There's a bluetit who has taken to sitting on the window rim of my car so that he can admire himself in the wing mirror. He gets quite annoyed when I need to use the car. Does he think he's found a mate? Or is he just vain?

H

[MAK]

We had a bullfinch that came to the kitchen window ( Spring) and would peck away at the window in a frenzy. One day it even left a small smear of its blood on the window - we then discovered that it may have been pecking at it's own reflection so I stacked some books on the kitchen window sill.
Maybe your bluetit sees his reflection and a possible "mating threat".

[Fleecewife]

We have had wagtails beating up the wing mirrors of our car.  They see their own reflection as a competitor.