The Torah tells us that a kosher land animal must chew its cud and have split hooves, and fish must have fins and scales. But the Torah doesn’t give any signs for the kosher bird. Instead, it lists 24 classes of non-kosher birds.
In theory, if we could identify these 24 classes, we could eat any class of birds not on this list (if slaughtered according to halachah). The problem is that many of the biblical-Hebrew bird names are not easily identifiable. (The English translations found in some Bibles are merely educated guesses, so some translators elect to transliterate rather than give inaccurate translations.) And even if we did know the exact English names, it would still be hard for most of us to identify the more exotic bird species. It would also be a challenge to identify which bird species belong to which classes, since the halachic categories differ from the common scientific ones (and the scientific categories are subject to change). For example, we don’t know how many species of birds fall under the category of “owl” or “eagle.”
To clarify this issue, the sages of the Mishnah give several signs that help identify whether a bird is kosher:
1) it is not a bird of prey; and
2) it has an “extra” toe, a crop, and/or a gizzard that can be peeled. (Whether all three of these signs must be present is a matter of dispute, as will be explained.)
Identifying Birds of Prey
In the words of the Mishnah, “Any bird that claws [lit., that is dores] is not kosher.” However, there are various opinions as to the exact definition of a dores:
a) a bird that seizes its food with its claws and lifts it off the ground to its mouth, b) a bird that holds down its prey with its claws and breaks off small pieces to eat,
c) a bird that hits its prey with its feet and ingests its prey while it is still alive,
d) a bird that pounces on its prey with its claws, or
e) a bird that injects a sort of venom into its prey.
The Mishnah adds an alternative method of identifying a bird that is a dores: a bird that “parts its toes,” i.e., when standing on a rope, it has two toes in the front and two in the back, like a parrot.
A 12th century rabbi, Rabbi Zerachiah Halevi of Gerondi (known as the Ba’al Hamoar), describes two features of a bird that is not a dores: a wide beak and webbed feet (like a duck).
Additional Signs of Kosher Birds
In addition to not being a dores, the Mishnah gives three features of a kosher bird:
- “Extra” toe: A toe that is behind and above the other toes. It is called “extra” because it is not in the same row as the other toes. Some say that this refers to an “elongated toe” (a front toe that is longer than the rest). Both of these characteristics can be seen in chicken feet.
- Crop: A pouchlike organ that stores undigested food until the digestive tract is ready to receive and digest the food.
- Peelable gizzard (pupik in Yiddish): A gizzard in the digestive tract that is lined with skin that can be peeled by hand.
While all agree that any bird of prey is not kosher, there are differences of opinion whether a bird needs to have all or some of these three features for it to be considered kosher. The Tzemach Tzedek writes that the halachah follows the opinion that all signs must be present --that is, unless there is a specific tradition that a bird is kosher.
In practice, it is difficult to identify birds by these rabbinic signs. Indeed, the Talmud cites a number of incidents where a community at first thought a certain bird was kosher, and only after a long while was it observed that the bird was in fact a dores and therefore not kosher. Thus, identifying a dores can be quite difficult, since even if the bird only exhibits the dores behavior very rarely, it is considered not kosher.
Therefore, the halachah is that we only eat birds that we know are kosher through established tradition. And if there is a reliable tradition that a bird is kosher, then it need not have all of the “kosher signs” (except for not being a predator). For example, the goose doesn’t have a crop but is nevertheless considered kosher.
Provided that we can only eat birds for which we have a tradition, the question arises, how is turkey, a New World species, widely considered kosher?
One explanation is that, in addition to the signs discussed above, the Talmud discusses a rule known as the hybridization principle: a kosher species cannot mate with non-kosher species. Therefore, the fact that a suspect species can interbreed with a known kosher species confirms the kosher status of the unknown species.
Although the Talmud does not explicitly state that this principle extends to birds, many rabbis, including the fourth Lubavitcher Rebbe, Rabbi Shmuel Schneerson, known as the Maharash, hold that it does indeed extend to birds, and therefore a bird can be considered kosher, even in the absence of a specific tradition, if it mates with known kosher species of birds.
Some, however, disagree and hold that this principle does not extend to birds, and they offer alternative explanations as to why most consider turkey kosher.
So although most species of birds are kosher, due to our lack of knowledge about many of the bird species, in practice, only birds for which there is a reliable tradition are eaten. Example of kosher birds are the domestic species of chickens, ducks, geese, turkeys and pigeons (doves).