THE SIMANIM OF BIRDS THAT ARE TAMEI
(Mishnah): The Torah did not give Simanim of Tamei and Tahor birds.
Question (Beraisa): "The Nesher (vulture or eagle)" - just like a Nesher has no extra toe, nor a crop, the skin of the stomach does not peel off, and it is Dores, also any bird with these Simanim is Tamei;
Just like a Tor (turtledove) has an extra toe, and a crop, the skin of the stomach peels off, and it does not Dores, also any bird with these Simanim is Tahor.
Answer (Abaye): The Simanim are not written in the Torah. They are part of the oral tradition.
(When we do not specify, 'Siman' refers to a Siman of Taharah.)
(R. Chiya - Beraisa): A bird with one Siman is Tahor, for it does not resemble a Nesher;
A Nesher has no Simanim, so it may not be eaten, but birds with a Siman may be eaten.
Question: Perhaps we should learn from Torim!
Torim have all four Simanim and are permitted. We should require all four Simanim to permit a bird!
Answer: If so, there would be no need for the Torah to list all the Tamei birds. (Each has at least one Siman of Tum'ah.)
Question: Why don't we learn from the other Tamei birds?
Some have three Simanim, yet they are forbidden. We should say that any bird with only three Simanim is forbidden, and all the more so if it has only one or two!
Answer: If so, the Torah would not have needed to say that a raven (which has two Simanim) is forbidden.
Question: Why don't we learn from the raven?
It has two Simanim, yet it is forbidden. We should say, any bird with at most two Simanim is forbidden, and all the more so if it has only one!
Answer: If so, the Torah would not have needed to explicitly forbid Peres (ossifrage?) and Ozniyah (a type of hawk), for each has only one Siman.
COULD WE LEARN THE SIMANIM FROM PERES AND OZNIYAH?
Question: Why don't we learn from Peres and Ozniyah?
Each has one Siman, yet it is forbidden. We should say that any bird with only one Siman is forbidden!
Answer: If so, the Torah would not have needed to say that a Nesher (which has no Simanim) is forbidden.
Rather, the Torah forbids a Nesher, which has no Simanim. This implies that a bird with a Siman may be eaten.
Question: We cannot say that had the Torah not written "Nesher", we would have learned from Peres and Ozniyah, for they are Shnei Kesuvim (two verses, one of which could have been learned from the other, in this case, that a bird with one Siman is forbidden). We do not learn from Shnei Kesuvim to elsewhere!
Answer: (Peres and Ozniyah are rare birds. Chachamim of the Gemara did not recognize them. Nevertheless,) we have a tradition that each has a different Siman than the other. (Therefore, we could not learn either from the other. Had it written only one, we would have thought that any bird with the other Siman is Tahor.)
Question: There are 24 Tamei species (almost all have three Simanim). Surely, some birds have the Siman of the Peres (and two others), and others have the Siman of the Ozniyah (and two others. Therefore, we would not have thought that any bird with the other Siman is Tahor!)
Since it was not necessary to write Peres and Ozniyah, they are Shnei Kesuvim!
Answer: We have traditions about the 24 Tamei species and the four Simanim:
Twenty species have the same three Simanim.
The raven has two Simanim;
The Peres and Ozniyah have different Simanim. (One of them has the Siman not found in any other Tamei species, so it could not be learned from them.)
Therefore, had the Torah not written Nesher, we would have learned it from Peres or Ozniyah;
Now that the Torah wrote "Nesher", we learn that a bird with even one Siman is Tahor.
Question: Why must the Torah write "Torim"? (Even birds with one Siman are permitted!)
Answer: The Torah must teach that Torim (and doves) are acceptable for Korbanos.