The Indians that were in the US before we took it over and killed most of them, had stories of what they called the Thunderbird, which is considered mythology in the modern era.
http://en.wikipedia.org/wiki/Thunderbird_(mythology)
Yet in their stories they told of large birds that would swoop down a carry their kids away.
The Golden Eagle has a wing spawn of about 7 feet. The California Condor has a wing span of about 9-10 ft on average.
Science has proven there were birds that were even larger, but even looking at that vid and seeing the Eagle was capable of almost getting lift you could somewhat assume that the extra 2-3 feet on a Condor could have likely gotten air-born. Perhaps even that Eagle could have if the parent's hadn't been there to scare it off.
Mother Nature isn't always pretty..
