a fuckbird, is one who fucks, or is being fucked by someone. normally, one who fucks often. its the equivalent of "lovebird" but instead of being one who loves, it is one who fucks.
Person A: Did you hear that Person C and Person D fuck each other whenever theres a party?
when, while hunting, you kill a particularly fine looking bird and decide to engage in intercourse with it, this is called a bird-fuck bird-cunt if and only if the birds cunt is stretched and torn when you are done.
That was a pretty sweet bird-fuck bird-cunt back there, eh skipper?
Skipper is a dog.