READER QUESTION: Are ducks considered to be “clean”?
We find 24 birds/classes of birds specifically forbidden in the Torah. These are mainly predatory and scavenger birds. Conversely, the Torah does not provide characteristics of kosher birds. So in general, if it is not and excluded bird, then it is okay. Thus, domestic species of chickens, ducks, geese, turkeys and pigeons/doves are considered clean/kosher.
I should add that while the Mishnah addresses "3 features of kosher birds," (a crop, extra toe, peelable gizzard), it is not at all clear how these features were derived, nor is there agreement in the Jewish community about them. For example, a goose does not have a crop, but is considered kosher.
Perhaps the "debate" about ducks includes what they eat? Ducks are "opportunists." They will eat small fish and fish eggs, snails, worms, slugs, frogs, tadpoles, crayfish, and other small amphibians. But they also eat grass, leaves, weeks, algae, and aquatic plants, seeds, grain, berries, fruit, nuts, and insects. Thus they are not "scavengers" or "predatory".