Eating turkey may be forbidden... for male descendants of R. Isaiah ben Avraham ha'Levi Horowitz unto the tenth generation?
"The Horowitz family, descendants of the Shlah haKadosh (Rabbi Isaiah ben Avraham ha'Levi Horowitz; 1565? - 1630), have a tradition that the Shlah supposedly left instructions that they should not eat turkey, and to this day there are members of that family who adhere to this custom."
"There is also a similar custom among the Lapidus family and other descendants of the Tosfot Yom Tov (Rabbi Yom Tov Lippman ben Nathan ha'Levi Heller; 1579-1654). These two traditions may share a common source."
See also Gilad J. Gevaryahu's comment.
So why is turkey considered kosher for others?
"The wild turkey has a crop, its gizzard is peelable, it has an "extra" toe, and its eggs have the indicators of kosher eggs, all signs indicating the turkey may be kosher," (Kashrut.com, op. cit).
"Shut Mei Be'er (Rabbi Yitzchak Isaac Schur, Bucharest, d. 1897; siman 19) opines that we eat turkey (indik) relying on the Jews of India, the place of origin of the turkey, who had a clear tradition dating back to Moses that the turkey was kosher. As far as he was concerned, the only question that ever existed with regard to turkey was whether Europeans could rely on the Indian mesorah and this, he claims, was settled in the affirmative by the Rivash.
"The Kaf Hachaim (YD 82:21) also permitted the turkey (tarnagol inglishi henner) based on the fact that it was eaten in India. Zivchei Zedek (82:17) in an apparent reference to turkey notes that in Iraq it was permitted and it originated in India, but he does not link the two statements. Nachal Eshkol (On Sefer ha'Eshkol, hilchot behama chaya v'of, 22:10) believed that 300 years before his time turkey came from India to England and then Germany and was now consumed without any hesitation." ibid.
If this is all there was to allow the kashrus of turkey, then it obviously is mistaken, since the bird is from olom chadash, not India or Iraq. However,
"The Lubliner Rav, Rabbi Eliyahu ben Rav Naftali Hertz Klatzkin (1852-1932) in Dvar Halacha (1921; siman 53, page 74)... permitted the turkey because he understood that the Ramo required a mesorah only for a new category of birds and that turkey falls within the same general category as chickens!" ibid.
A modern "proof" of acceptability is based on hybridization:
"Turkey-chicken hybrids... have been successfully produced and are used in scientific research... [C]rosses between ring-neck pheasants and chickens and between ring-neck pheasants and turkeys are well documented... and may provide yet another avenue to permit turkeys. If hybridization between species is a legitimate test of kosher status, and many authorities accepted that it is, these crosses verify the acceptability of pheasant, and then confirm the status of turkey."
That said, chicken-turkey hybrids, "were literally twisted. They had crooked legs, beaks and feathers. Adding insult to injury, the churks were only half as smart as their parents." So of all indications that turkeys are kosher, to me, this seems most suspicious.