(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 of cattle and a wild animal are stated from the Torah, but the signs of a bird are not stated. But the Sages said, "Any bird which attacks [prey] is prohibited. Any that has an extra digit, a crop, and gizzard that peels [away] is permitted." Rabbi Eliezer ben Rebbi Tzadok says, "Every bird which parts its toes is prohibited."
(ג) יֵשׁ אוֹמְרִים שֶׁכָּל עוֹף שֶׁחַרְטוֹמוֹ רָחָב וְכַף רַגְלוֹ רְחָבָה כְּשֶׁל אַוָּז, בְּיָדוּעַ שֶׁאֵינוֹ דּוֹרֵס, וּמֻתָּר בַּאֲכִילָה אִם יֵשׁ לוֹ שְׁלֹשָׁה סִימָנִים בְּגוּפוֹ. הַגָּה: וְיֵשׁ אוֹמְרִים שֶׁאֵין לִסְמֹךְ אֲפִלּוּ עַל זֶה, וְאֵין לֶאֱכֹל שׁוּם עוֹף אֶלָּא בַּמָּסֹרֶת שֶׁקִּבְּלוּ בּוֹ שֶׁהוּא טָהוֹר (בְּאָרֹךְ כְּלָל נ''ו ובתא''ו נט''ו), וְכֵן נוֹהֲגִין, וְאֵין לְשַׁנּוֹת.
(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. Gloss: 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.
The "Gloss" is a commentary by Rabbi Moshe Isserles (the Rama), who provides a mainstream halakhic ruling for Ashkenazim. The main next of the Shulkhan Arukh was written by Rabbi Yoseph Karo in the mid-16th century, and its rulings are those of the Sephardic community of Tzefat. In this case, Isserles seeks to end an argument regarding a lack of clarity regarding signs of kashrut on birds.