Dr. Kenneth E. Campbell, (one of the discoverers) in front of the 25 ft. wingspan Argentavis Magnificens. Display seen at the Natural History Museum, Los Angeles. The feather size from such a bird is estimated to have been 1.5 meters long (60 inches); and 20 centimeters wide (8 inches). Such a huge size would make the feather at least 5 feet long, similar to the one described as coming from the Desert Southwest in:
Also known as the "teratorn" and the Legendary Thunderbird.
The site link above is to one such Thunderbird site.
This may be at least part of the legends concerning the "Roc" ( or Rook? ) of Arabian Tale's and Sinbad fame.
As to flight, the article refers to places like the Andes and Argentine Pampas as having the wind currents necessary for flight.
I suggest the Great Plains, Rockies and Appalachian mountains of North America could also have provided habitat for what the Native Americans called the Thunder Bird.
Anecdote suggests the Thunder Bird also utilized storm fronts as lifting forces to travel large distances. ( And possibly for takeoffs in lower altitudes )
These birds probably fall into the category ( class? ) of Mammoth, Giant Sloth, Giant Elk, Cave Bear, etc. that disappeared about the same time ancient man began colonizing the americas.
That would date some of the oral legends handed down as much as 25,000 years, 10 to 12,000 for the Clovis cultures.
