UPDATE: Bird people (!!!!!)
Original Story: "Red Dead Redemption" features some impressive animal AI which allows beasts of all kinds to populate the wildest parts of the Wild West. Unfortunately it seems this AI has run afoul of some human DNA and created monstrosities not seen since "The Island of Doctor Moreau."
Two videos have been unleashed on YouTube which show off the glitch. Currently there is public record of a Donkey Lady (!) and a Cougar Man (!!!). Given the bugged nature of the animations, I'm gonna assume that these abominations were unintentional side effects of the animal population system in the game and are not subtle nods to terrible horror movies.
It seems that there's no consistent way to recreate these bugs, but if you happen to spot a half-man, half-vulture circling high above the plains, make sure you capture it on film and upload it to your local internet dispensary. You could become internet famous!
(Interestingly this isn't the first time a Rockstar game has featured rare mythical beasts in some way. For years, rumors circulated about the appearance of Bigfoot somewhere in the hills of San Andreas. Unlike Donkey Lady and Cougar Man, though, no video evidence was ever presented, so his existence remains suspect.)