A guttershrike is a species of aquatic bird resembling a scrawny cormorant or shag. They have strange habit of waiting in car parks and when the owners of cars leave their vehicles the guttershrikes will descend upon the cars (or other motor vehicles) and tear off any rubber they can get at. They will also smash wing mirrors and take the pieces of glass. They then weave these pieces of rubber into their nests. Nasty little sods.