Birds

If there's nearly one thing universal in Native American mythology it is giant birds, monster birds, even the Thunderbird (which has been adopted as a brand name for many products not to mention the name of a TV show with associated spin-off motion pictures). Now apart from the actual observations of these winged monstrosities, there's nothing all that unusual about giant flying creatures in mythology. What sets these 'birds' apart is that they often like to snack on the natives - as takeaways, not dine in. Is there any natural terrestrial explanation for birds carrying away humans, like a crow picking up a kernel of corn? Or, might one have to resort to another, more unnatural and perhaps extraterrestrial explanation?