"Origins of the Thunderbird"
"Myth Cryptozoologists like Mark A. Hall, having studied the Thunderbird myths
of numerous tribes, and compared them to (mostly folkloric) accounts of unusually large
birds in modern times, as well as large birds (like the Roc) in other mythic traditions, suggest
that there may well be a surviving species of large avians in America - big enough, apparently,
to fly off carrying small animals or children, as has been claimed in some accounts. (Hall suggests the wingspan of such a species would be several feet longer than any
known birds - certainly bigger than that of the turkey vulture or other identifiable
North American species.) (Hall 1988) Such researchers feel the Thunderbird myth may have
originated from sightings of a real-life flesh-and-blood avian which might be an atavism
from earlier epochs (a quasi-pterodactyl or teratorn, perhaps.)"