Israelis eat more turkey per capita than residents of any country in the world (probably due to the large number of schwarma stands and the readily available lunch meats) so how can we even think that turkey may not be kosher?
In Parshat Shmini (Vayikra 11:13-19), we read about the species of birds that are not Kosher (since we don’t know the exact translations of what these birds are today, I am using the original Hebrew names of the birds with the probable English translations in parentheses):
These shall you abominate from among the birds, they may not be eaten- they are an abomination: the nesher (eagle), the peres (bearded vulture), the ozniah (sea eagle), the da’ah (falcon), the ayah (vulture), to its kind. Every orev (raven), to its kind. The Bat HaYa’anah (ostrich), the tachmas (owl), the shachaf (seagull) and the netz (hawk), to its kind. The kos (little owl), the shalach (heron) and the yanshuf (eagle owl). The tinshemet (bat), the kaas (pelican) and the racham (carrion vulture). The chasida (stork), the anafah (heron) according to its kind, the duchifat (hoopoe) and the atalef (bat).
In Parshat Re’eh, Dvarim 14:11-20 we do not just learn about what we can’t eat, but also what we can eat:
Dvarim 14:11 states: You may eat any pure bird.
After an almost identical list of birds that are not permissible, with the addition of a bird called the ra’ah (from the family of the da’ah and the ayah) we are informed in verse 19:
And all flying creeping creatures are ritually unclean for you. They may not be eaten.
Then the whole segment is capped off with (verse 20): Every ritually clean bird you may eat.
From here we should conclude that if the bird is not one of the 24 species (20 listed + 4 times where it says “to its kind”) then it is kosher.
The only problem is that we don’t know the exact translations of what these birds are today, so we can’t guarantee that they will be accurately identified.
We learn in the Mishna Chulin 3:6:
The signs of a kosher bird were not explicitly stated in the Torah. 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.
Shulchan Aruch- Yoreh Deah 82:3 teaches: 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 takes a stricter approach: 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 (Arukh) and we are accustomed to this and it should not be changed.
According to the Rama, in order not to make a mistake, over the generations, only birds that have traditionally been known to be kosher were eaten.
This brings us back to turkey which was a new world bird, only introduced to Europe in the 16th c, the time period when the Rama lived.
One possible answer is that the turkey made it in right on time. It had the signs of a kosher bird as explained by the mishna and it was already being eaten before it was taught that there must be a mesorah (accepted tradition).
As well, since the turkey can mate with chickens, they can be looked at as their relatives making them permissible as well.
So go ahead and enjoy your turkey but if you come across a bird that you don’t recognize, even if it fits into all of the categories, chances are that the rabbis will not permit it as it was not part of the mesorah.