The Torah itself only names the forbidden bird species, listing twenty-four non-kosher types, without giving any signs for a kosher bird, as seen in the list of abominated birds in Vayikra 11:13-19 and the corresponding permission of 'any pure bird' in Devarim 14:11-20. Chazal filled this gap by articulating physical signs of kashrut — that a bird is kosher if it does not claw and devour prey, and has an extra digit, a crop, and a gizzard that can be peeled — as stated in the mishna of Chullin 59a and elaborated through the paradigm cases of the nesher and the dove in Chullin 61a.
Beyond the physical signs, the Gemara in Chullin 63b:11 establishes an independent criterion of mesorah (received tradition): a bird is eaten as kosher based on a hunter's or community's transmitted tradition that it is a kosher species, and this is codified by Shulchan Arukh, Yoreh De'ah 82:1-3 and Mishneh Torah, Forbidden Foods 1:16, while Mishneh Torah, Forbidden Foods 1:20 adds that a bird which dwells among and resembles non-kosher birds is itself rendered non-kosher. The Tur in Tur, Yoreh De'ah 82 and the Chokhmat Adam in Chokhmat Adam 36:1-2 restate these same signs and the requirement of checking for the clawing behavior and the peelable gizzard.
The Gemara in Chullin 62b and Chullin 59b and Chullin 66b catalogues specific uncertain or named bird species whose gizzard can only be peeled with a knife rather than by hand, rendering their status as kosher or not a matter of dispute among the tannaim, showing that the classification of a bird as a kosher min is often fact-specific and contested even for known ancient species.
This question of signs versus mesorah becomes sharply relevant for birds newly encountered in later centuries, since Arukh HaShulchan, Yoreh De'ah 82:29 records the position that one may not rely on physical signs alone without a received tradition, and the Beit Yosef in Beit Yosef, Yoreh De'ah 82:7 cites the precedent of the tarnegolta de'agma, a bird once assumed kosher that was later observed clawing its prey, as grounds for insisting on mesorah rather than signs alone.
Applying this directly to newly discovered fowl, the Darkhei Teshuvah in Darkhei Teshuvah, Yoreh Deah 82:46 and Darkhei Teshuvah, Yoreh Deah 82:28 records debates over new breeds of chickens brought from America and elsewhere, with some authorities refusing to permit them absent an established mesorah even where the signs of kashrut are present, and a parallel debate over an unfamiliar bird is recorded in Darkhei Teshuvah, Yoreh Deah 82:38. The Kaf HaChaim in Kaf HaChaim, Yoreh De'ah 82 and the Shoel uMeshiv in Shoel uMeshiv Mahadura III 1:149 likewise discuss specific newly-arrived fowl, in the latter case ruling leniently that a species resembling local chickens and able to interbreed with them was permitted, while Melammed Lehoil Part II 16 discusses the pheasant along similar lines, citing testimony that it was eaten in Italy without concern.
Rav Eliezer Melamed addresses the turkey directly: in Peninei Halakhah, Kashrut 17:6 he notes that some raised the question of its kashrut precisely because it originates from America, discovered only in 1492, and therefore lacks a mesorah from the time of the mishna even though it possesses all the signs of a kosher bird listed by Chazal; nevertheless, he states that the accepted practice (citing the Knesset HaGedolah) is to treat it as kosher, reasoning that the early rabbis who first encountered it considered it not a new species but merely another breed of chicken, for which no independent mesorah is required.
Ma'ayan Omer, in Maayan Omer 4:3:16, rules on a related practical detail concerning turkey eggs, holding that their veins should be cut before salting, even though this particular requirement is supported by only one cited source.
Igros Moshe, in Igros Moshe OC 5:20, takes up a different practical question touching the turkey — whether eating turkey on Thanksgiving is problematic even for one who does not participate in the associated festive gathering — and concludes that such a concern is unlikely to apply to the conduct of ordinary non-Jews.
