(1) דוכיפת is the wild rooster, which is called in old French herupe, and which has a double comb (Chullin 63a; cf. Rashi on Leviticus 11:19).
(ו) סִימָנֵי בְהֵמָה וְחַיָּה נֶאֶמְרוּ מִן הַתּוֹרָה, וְסִימָנֵי הָעוֹף לֹא נֶאֱמָרוּ. אֲבָל אָמְרוּ חֲכָמִים, כָּל עוֹף הַדּוֹרֵס, טָמֵא. כֹּל שֶׁיֶּשׁ לוֹ אֶצְבַּע יְתֵרָה, וְזֶפֶק, וְקֻרְקְבָנוֹ נִקְלָף, טָהוֹר. רַבִּי אֱלִיעֶזֶר בַּר צָדוֹק אוֹמֵר, כָּל עוֹף הַחוֹלֵק אֶת רַגְלָיו, טָמֵא:
(6) The signs that indicate that a domesticated animal and an undomesticated animal are kosher were stated in the Torah, and the signs of a kosher bird were not explicitly stated. But the Sages stated certain signs in a bird: Any bird that claws its prey and eats it is non-kosher. Any bird that has an extra digit behind the leg slightly elevated above the other digits, and a crop, which is a sack alongside the gullet in which food is stored prior to digestion, and for which the yellowish membrane inside its gizzard can be peeled, is kosher. Rabbi Elazar, son of Rabbi Tzadok, says: Any bird that splits the digits of its feet when standing on a string, placing two digits on one side of the string and two on the other, is non-kosher.
(ב) כל מי שהוא בקי באותם מינים ובשמותיהם הרי זה אוכל כל עוף שאינו מהם ואינו צריך בדיקה (שם) ועוף טהור נאכל במסורת והוא שיהיה דבר פשוט באותו מקום שזה עוף טהור ונאמן צייד לומר עוף זה התיר לי רבי הצייד והוא שיוחזק אותו צייד שהוא בקי במינים הטמאים האמורים בתורה ובשמותיהם. מי שאינו מכירם ואינו יודע שמותיהם בודק בסימנים כל עוף שהוא דורס ואוכל בידוע שהוא ממינים הטמאים ואם אינו יודע אם דורס אם לאו אם כשמעמידים אותו על חוט חולק את רגליו שני אצבעותיו לכאן וב' אצבעותיו לכאן או שקולט מן האויר ואוכל בידוע שהוא דורס ואם ידוע שאינו דורס יש שלשה סימני טהרה אצבע יתירה וזפק וקורקבנו נקלף ביד לאפוקי אם אינו נקלף אלא בסכין (ל' המחבר) היה חזק ומדובק והניחו בשמש ונתרפה ונקלף ביד הרי זה סימן טהרה ואע "פ שיש לו ג' סימנים אלו אין לאכלו לפי שאנו חוששין שמא הוא דורס אלא א"כ יש להם מסורת שמסרו להם אבותיהם שהוא טהור. (ל' הרמב"ם שם די"ח):
(2) Anyone who is an expert in those types and their names, behold he eats all of the birds that are not from them, and he doesn't need checking. (Ibid.) And a kosher bird is eaten according to tradition, and that is the clear thing in that place that it is a kosher bird. And the hunter is believed saying: This bird, my hunting rabbi permitted for me, since that hunter is known to be in an expert in non-kosher types that are mentioned in the Torah and their names. Someone who does not know them and does not know their names, he should check the signs: ... And even though it has these three signs, it should not be eaten, because we are concerned lest it is a bird of prey, rather, unless they have a tradition that was transmitted to them by their ancestors that it is kosher. (See Rambam Forbidden Foods 1:18).
(ג) יש אומרים שכל עוף שחרטומו רחב וכף רגלו רחבה כשל אווז בידוע שאינו דורס ומותר באכילה אם יש לו שלשה סימנים בגופו: הגה ויש אומרים שאין לסמוך אפילו על זה ואין לאכול שום עוף אלא במסורת שקבלו בו שהוא טהור (בארוך כלל נ"ו ובתא"ו נט"ו) וכן נוהגין ואין לשנות:
(3) There are those who say that all birds that have a wide beak and the palm of its foot is wide like a goose, and it is known that it is not a bird of prey, and is permitted to eat if it has the three signs on its body. Rama: And there are those who say that we don't rely even on this, and one should only eat a bird with an accepted tradition that it is kosher (in the Arukh...) and we are accustomed to this and it should not be changed.
Arugas Habosem (pp. 16) says that the mesorah is only required to prove that it is not a doreis. If the bird is monitored for at least twelve months, one may rely on the kosher status of the bird even without having a mesorah on it, as it is obviously not a dories.
Shoel U’Meishiv (5:1:69) posits that turkey has all three simanim and is not a doreis, end of story. And what of the Ramah about needing a mesorah? There is no mesorah for a turkey, and it must be that klal yisrael did not fully accept this Ramah. In other words, we do not hold like Ramah’s opinion, and if a bird has the simanim which indicate a kosher status we may eat it even without a mesorah.
Rabbi Hershel Schachter: Columbus was from Spain, and so when he returned from America back to Spain, he brought the turkeys back with him. Thus, the mesorah we have today comes from the Jews of Spain, who have a long and rich history. Or, Columbus discovered America 1492, some 48 years before Ramah was born (in 1540). Thus, it seems that a sound sevara would be that Jews began eating turkey based on its kosher simanim alone, without a requirement for mesorah, as Ramah didn’t write his opinion yet!
Rav Joeseph B. Soloveitchik: It was the opinion of Rabbi Soloveitchik that it was permissible to eat turkey at the end of November, on the day of Thanksgiving. We understood that, in his opinion, there was no question that turkey did not lack a tradition of kashrut (36) and that eating it on Thanksgiving was not a problem of imitating gentile customs. We also heard that this was the opinion of his father, Rabbi Moshe Soloveitchik.