Could it be that aliens took some of our animals for preservation and then put some back just recently?

For instance the giant birds people keep seeing and Nessie and many other animals. Maybe, just like we do with endangered species they do the same with our animals and then reintroduce them hundreds of years later, maybe they only put one or two back to test if they could survive be for returning more. I know this is a very odd question but try to keep an open mind and have fun with it. I have no proof and im not sure if these sighting are even true. The bigfoot could be a taken caveman who has been captive or bred or frozen and then returned years later. What do you think, any answers and opinions would be great. Have a good day