Why does the carrion-crow of America differ materially from the bird so common in England?

Because of its greater rapacity as well as tameness. Thus, in the cities where they are protected, they enter the very kitchen, and feed on whatever is thrown to them, even vegetables. If unmolested, they will remain in the same premises for months, flying to the roof at dusk to spend the night. Six or seven are often seen standing, in cold weather, round the funnel of a chimney, apparently enjoying the heat from the smoke. Notwithstanding the penalties imposed by law, a number of these birds are destroyed on account of their audacious pilfering. They seize young pigs as great dainties. They watch the cackling hen, in order to get the fresh egg from her nest; and they will not hesitate to swallow a brood of young ducks. In order to keep them from the roofs of houses, where their dung is detrimental, the inhabitants guard the top with broken pieces of glass fastened in mortar; and they often kill them by throwing boiling water upon them. No fewer than two hundred of these birds are daily fed by the city of Natchez. - Audubon.