http://revach.net/article.php?id=1398

Section: Halacha   Category: Tshuvos
How Do We Know Turkey Is Kosher? - Was Columbus The First Jew in America?
The Shulchan Aruch (YD 82:3) gives simanim of a kosher bird, however the Rema argues and says that without a mesora we cannot eat any birds even if it has simanim.  The question that many poskim discuss is how can we eat Turkey, which is an American bird that was transported back to Europe after the discovery of America, and cannot possibly have any mesora.

The Darkei Teshuva (YD 82:26) considers a number of explanations from various poskim.  Regarding the fact that there was a mesora in India for Turkey, he says that the Rashba holds that one country cannot rely on another country's mesora.  Another explanation that he brings from the Meishiv Davar is that the Rema banned any bird without a mesora only if it is newly discovered.  Since Turkey had been eaten for many years before the question came up, we cannot question our predecessors logic in permitting it, even if they did not have a mesora, and we cannot assur it and spread a bad name on them.

He also brings the Arugas HaBosem that says that the Rema only forbid birds whose simanim are not 100% guaranteed, but since we have watched Turkeys now for hundred of years and they without a doubt possess all the simanim without exception, we can eat it without a mesora.

The Sichas Chulin in an admittedly wild theory says that during the time of the exile of the Aseres HaShevatim, some of them ended up in America.  They had a Mesora on Turkey and passed it on to the exiles of the Spanish inquisition, who passed it back to Europe.

Important Note: We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.