Gemara

(Beraisa - R. Gamliel): Any bird that is Dores is Tamei;

If it has an extra toe, a crop, and the stomach can be peeled, it is Tahor;

62a (Ameimar): The law is, if a bird has a Siman, it is Tahor, as long as it is not Dores. The only Tamei species that is not Dores is Peres or Ozniyah. These are not found in settled areas, so we are not concerned for them.

62b (Rav Papa): The hen of the swamp is permitted.

Mereimar: Later, Chachamim saw the hen of the swamp be Dores. They forbade it.

63b (R. Yitzchak): One needs a tradition to eat a species of bird. A hunter is believed to say that his teacher told him that a certain species is Tahor.

(R. Yochanan): He (the teacher) must know the names and recognize the Tamei species.

Question (R. Zeira): Does this refer to his Rebbi who taught him Torah, or the one who taught him how to hunt?

Answer: R. Yochanan said that he must know the names and recognize the Tamei species.

This is reasonable regarding the one who taught him how to hunt.

A Chacham would know the names, but he would not recognize all the Tamei species!

Rishonim

Rambam (Hilchos Ma'achalos Asuros 1:15): Anyone who is expert in the (24 Tamei) species and their names, he may eat any bird not from them. He need not check (Simanim). One may eat a Tahor bird based on tradition, if it is clear in that place that it is Tahor. A hunter is believed to say 'my hunting teacher taught to me that this is bird is Tahor, if that hunter is established to be expert in the Tamei species explicit in the Torah and their names.

Rosh (3:59): Rashi says that since we are not experts, if a bird comes in front of us, we must be concerned lest it be Dores. Chachamim held that the hen of the swamp is Muchzak to be Tahor, and later they saw it be Dores. For any bird, we may eat it only if we have a tradition. If we have no tradition, we must be concerned. We may rely on tradition, like it says in 63b.

Rosh (60): If one goes from country to country, and in his current location they have a tradition to permit a particular bird, but they do not in his origin, he may eat it there, even if he intends to return. We do not place on him the stringencies of his origin, for they do not hold that it is forbidden. They just lack a tradition. We may rely on the tradition of his current location. One may rely on them to eat it anywhere, as long as there is no proof that it is forbidden. The Ba'al ha'Ma'or cites a tradition from early Chachamim that any bird with a wide beak, or the Kaf (ball) of its foot is like a goose's, we know that it is not Dores. Presumably, this is correct. We may eat it of it has three Simanim on the body. We are not concerned lest it is Dores.

Magid Mishneh (20): The Rashba relied on the Ba'al ha'Ma'or's tradition.

Shulchan Aruch (YD 82:2): Anyone who is expert in the species and their names, he may eat any bird not from them. He need not check. One may eat a Tahor bird based on tradition, if it is clear in that place that it is Tahor. A hunter is believed to say 'my hunting teacher taught to me that this is bird is Tahor, if that hunter is established to be expert in the Tamei species explicit in the Torah and their names.

Shach (1): The Gemara concludes that he is not believed to say that a Chacham told him that it is Tahor. The Yam Shel Shlomo (3:115) says that if a Chacham testifies that he has a tradition that a bird is Tahor, he is believed, especially nowadays that we do not have (expert) hunters, just tradition.

Shach (2): The hunter's Rebbi must be an expert.

Shulchan Aruch (ibid.): Even if it has the three Simanim, we do not eat it, for we are concerned lest it is Dores, unless he has a tradition that it is Tahor.

Shach (4): Our custom is to forbid even if it is not Dores, for we are concerned lest it be Dores at another time, unless it has a wide beak or the base of its foot is like a goose's, and it has the three Simanim of Taharah.

Shulchan Aruch (3): Some say that any bird with a wide beak, or the ball of its foot is like a goose's, we know that it is not Dores, and one may eat it if it has the three Simanim on its body.

Beis Yosef (DH u'Mah she'Chasav Rabeinu b'Shem): It seems that the Rosh, Rashba, Ran, and Magid Mishneh all accepted the Ba'al ha'Ma'or's tradition. They all say or the ball of its foot is like a goose's. This implies that one of these Simanim suffices to show that it is not Dores. Why did the Tur write and the ball is like a goose's? The Rashba (1:212) was asked about this, and said that he cannot answer, for he did not see the Gaon who said so. It connotes that the primary text is 'v'Kaf' (which can mean 'and' or 'or' - PF).

Shach (7): It seems that the Shulchan Aruch requires both of these. The Beis Yosef and Acharonim concluded like this.

Shach (8): The Yam Shel Shlomo (3:115) says that three Simanim on the body suffice even nowadays, for then we know that it is not Dores. However, he must ensure that the crop is shaped like other crops. We are not concerned if it is smaller. Then, even if we see that it is Dores we are not concerned. It was an aberration (but the species is not Dores). I say that one may not be lenient.

Rema: Some say that we do not rely even on this. One should not eat any bird without a tradition that it is Tahor. This is the custom. One should not deviate.

Beis Yosef (DH u'Mah she'Chasav Rabeinu v'Rashi): The Tur says that Rashi requires a tradition to eat any bird. This is based on 62b. The hen of the swamp was Muchzak to be Tahor. Later, Chachamim saw it be Dores, so they forbade it. Likewise, if a bird comes in front of us, we must be concerned lest it be Dores, unless we have a tradition that it is Tahor. We may rely on tradition. It seems that the Rosh rules like Rashi, in his Pesakim and a Teshuvah (20:32). R. Yerucham says that this is primary. The Rashba says that if a bird has an extra toe, a crop, and the stomach can be peeled by hand, it is known that it is not Dores. Other birds that have some Simanim, some are permitted and some are forbidden. Therefore, we require a tradition.

Taz (4): How can it be that people ate the hos, and afterwards they found that it is Tamei? Hash-m does not bring a pitfall (regarding eating) even through the animals of Tzadikim (Chulin 5b)! Tosfos (Gitin 7a DH Hashta) says this means only that a Tzadik himself will not eat Isur. If so, we can say that the masses ate through the ruling of Chachamim.

Shach (9): We require a tradition, and then one does not need any Simanim. Isur v'Heter (56:18) explicitly says so, but then he requires three Simanim! This is astounding. This is why the Rema omitted Isur v'Heter's opinion.

Meshov Davar (2:22): Many protested when Indik (turkey) were brought from India, without a tradition for their Kashrus. The custom is to permit, and no one protests. This is because they became Muchzak to be permitted, and there is no proof to forbid. I lean to permit big geese, if some Gedolei ha'Dor will agree.

Darchei Taharah (82:26): Nachal Eshkol discusses Indisha Heners that came 300 years ago from Hodu (India; really, they came from America) to England. Therefore, they are called English hens. We eat them without question, even though they are very unlike our chickens. They are twice as high, long and wide, and their heads are different. There is dangling red skin under their heads. What is the source of the Heter to eat them? People in the east eat them, but the Rashba says that a country may not rely on the tradition of another country! Also Sho'el u'Meshiv asks why we eat them in all countries in which Yisre'elim live. Mei Be'er (19) says that people of India had a tradition from Moshe Rabbeinu that turkey is Tahor. The question was whether others may rely on it. The Rivash permitted. I did not find this in the Rivash, or any Rishon or Acharon. and I did not find an argument about this.

Afarkasta d'Anya (2:125): There is a city that has always permitted big geese. If it came in front of me at first, I would not permit it, for it is different from our geese. It needs a tradition. However, since they were already eating it, we are not stringent until we have a proof. The Rema is stringent to require a tradition only regarding a new bird that we did not hear about. If people have been eating a bird with three Simanim, and it dwells with a known Tahor bird and resembles it, even though there was no tradition for it, we do not forbid it and say that our ancestors ate a Tamei bird. This is why we eat turkey. When it was brought from India, there was no tradition for it. Even nowadays some are stringent, but the custom is to permit and no one protests.

Sichas Chulin (p.429): Dameshek Eliezer (51:84) says 'wild chickens that we call 'English hens' are permitted, even though its Hod\ is bent like that of a Duchifas (hoopoe, i.e. wild hen). It has all of the Simanei Taharah, and also what it says in Eruvin (100b, that a rooster spreads its wings before relations, and afterwards bends down its head. This shows that turkeys are considered chickens. - PF) Also Keneses ha'Gedolah says that they are Tahor. The Mishnah Berurah (79:26) connotes like this. (He says that the excrement of red chickens, which we call 'English hens', is very putrid. One should not keep them in the house, for people learn and bless there.) Arugas ha'Bosem says that any bird that we recognize and raise tens of thousands of them and we see that they are not Dores, we do not need a tradition for it. How else can we explain why Gedolim permitted turkeys? When America was discovered, there was no tradition for them, since there were no Yisre'elim there!

Sichas Chulin: Perhaps there were Yisre'elim there from the exiled 10 tribes, and they had a tradition from the days of Moshe, and they gave the tradition to Yisre'elim who fled the Inquisition. This is like Mei Be'er said. (He said that the tradition was from India. Those who discovered America initially thought that it is India.)