For several weeks, we have observed the puzzling behaviour of a male bullfinch attacking and fouling car door mirrors and some buildings' windows. In fact, there may be quite a few of them, as they can all look alike. An attack can go on for hours and seemingly, days. The species is becoming a pest, protected in law, leaving surfaces spattered and smeared with poo. We've learnt to recognize the noise of an attack, which can be heard through double-glazing from a vehicle parked outside.
Searching for a non-lethal counter-measure, some small black opaque laptop sleeves were found which fitted snuggly over the car-door mirrors. Using them, the birds cannot see their own reflection in the mirrors, and so do not attack it. We'll see how it goes.