Brown-headed Cowbird, Molothrus ater
I have often heard the Brown-headed Cowbird maligned as villainous and deceitful, even by fellow birders. Somehow or other we wish to assign to the cowbird values held dear by humans (well, some humans at least) and seek to impose on it our notions of what is proper care of a family by the parents. I even once knew a birder who would routinely shoot cowbirds at every chance he got.
We should simply accept the fact, perhaps even rejoice in it, that the entire suite of birds we know as brood parasites, have evolved a highly successful life style that ensures the continued existence of their species, and stop anthropomorphizing at every turn. I think that if the cowbird's behaviour was replicated in human terms it would be declared "Entrepreneur of the Year."