Littergulls

They are on the lookout continually for any take-away food containers accessible to them at the top of a full-ish litter bin (sometimes they even get inside...). I think they favour the polystyrene ones because they can stab them open with their brutal beaks. Occasionally they'll get one impaled on the beak, which I find very funny but they don't. (Sorry, this one didn't or it would have made a better blip!)