מה נשר מיוחד שאין לו אצבע יתרה וזפק ואין קורקבנו נקלף ודורס ואוכל טמא אף כל כיוצא בו טמא תורין שיש להן אצבע יתרה וזפק וקורקבן נקלף ואין דורסין ואוכלין טהורין אף כל כיוצא בהן טהורין אמר אביי לא נאמר פירושן מדברי תורה אלא מדברי סופרים
Just as a nesher is unique in that it has no extra digit or crop, and its gizzard cannot be peeled, and it claws its prey and eats it, and it is non-kosher, so too, all like birds with these four signs are non-kosher. And just as doves and pigeons, which have an extra digit and a crop, and whose gizzard can be peeled, and do not claw their food and eat it, are kosher, as they are fit for sacrifice on the altar (see Leviticus 1:14), so too, all like birds with these four signs are kosher. If so, why does the mishna state that the signs were not stated in the Torah? Abaye said: The mishna means that the explanation of the signs of a kosher bird was not stated in the Torah. Rather, one learns it from the statements of the Sages, i.e., the baraita.
תני רבי חייא עוף הבא בסימן אחד טהור לפי שאין דומה לנשר נשר דלית ליה כלל הוא דלא תיכול הא איכא דאית ליה חד תיכול
Rabbi Ḥiyya teaches: A bird that comes before a person with one sign of a kosher bird, and which is not listed in the Torah as non-kosher, is kosher, since it is unlike a nesher. The verse did not need to state that the nesher is non-kosher, since one could have inferred this from the list of other non-kosher birds. Rather, the verse mentions the nesher specifically to indicate that it is only a bird like a nesher, which has none of the signs of a kosher bird, that you shall not eat. But if there is a bird that has even one of the signs, you may eat it.
ולילף מתורין מה תורין דאיכא כולהו ארבעה אף ה"נ עד דאיכא כולהו ארבעה
The Gemara asks: But why learn specifically from the case of a nesher? Let one derive the opposite from the case of doves: Just as doves, which the Torah mentions explicitly as kosher, have all four signs, so too here, no other bird is kosher unless it has all four signs.
אם כן שאר עופות טמאין דכתב רחמנא למה לי
The Gemara responds: If it is so that one learns from the case of a dove, why do I need the rest of the non-kosher birds that the Merciful One wrote? Since none of them has all four signs of a kosher bird, their non-kosher status could simply be inferred from the case of a dove. Rather, since the Torah states explicitly that they are non-kosher, it follows that one does not learn from the case of a dove.
ונילף מינייהו מה התם תלתא ולא אכלינן אף כל תלתא ולא ניכול וכל שכן תרי וחד
The Gemara objects: But let us derive instead from them, i.e., the rest of the non-kosher birds, which each have only three signs, the following: Just as there, those birds have three of the signs of a kosher bird mentioned in the mishna, and we still do not eat them, so too, all other birds that have three signs should have the same halakhic status, and we will not eat them. And all the more so should this apply to a bird that has only two signs or one.
אם כן עורב דכתב רחמנא למה לי השתא דאית ליה תלתא לא אכלינן דאית ליה תרי מיבעיא
The Gemara responds: If so, why do I need the crow that the Merciful One wrote among the non-kosher birds? Now that it is established that we do not eat any bird that has three signs, is it necessary to mention the crow, which has only two? Rather, those birds explicitly listed as non-kosher are prohibited, and all other birds with any number of signs are kosher.