Heritage Turkeys, as defined here, are turkeys which have a historical or contemporary use in the US, and which are still obtainable, and free of genetic or behavioral issues which interfere with sustainability.
The APA insists that all Turkeys are a single breed, and that the differences are only enough to constitute a "variety" rather than a "Breed". The APA has no authority to define this, they just do, and nobody protests, in spite of the fact that in this instance, they are dead wrong.
The differences in Turkey breeds in the US are more than size or color. They are also behavioral, involve differences in conformation, beard characteristics, and meat characteristics, and some are no longer able to mate naturally.
Turkeys listed here are listed as Breeds.