Some parrots from the same species are capable of killing each other, but I think this is quite rare, unless it is in the case of territorial birds or male parrots competing for a female. read more
Parrots have definitely been known to kill one another or die of injuries sustained in fights, but I don't imagine they sit around plotting murder in the sense that some humans do. I'm convinced that my green cheek conure and sun conure would kill one another if given enough time alone without supervision. read more