Of all clean birds ye shall eat. Which the Targum of Jonathan describes, everyone that has a craw, and whose crop is naked, and has a superfluous talon, and is not rapacious; but such as are unclean are expressed by name in the following verses, so that all except them might be reckoned clean and fit for food. Maimonides p observes, that only the number of the unclean are reckoned, so that all the rest are free.
p Hilchot. Maacolot Asurot, c. 1. sect. 14.