Alright shadowfag, here's the nail in the coffin.
Watch the first video of another bird flying across the sky well before the plane even comes into the picture. It too has a shadow in front of it. Its just a video artifact from the bird moving so fast and the FPS not being high enough to capture it fully.
Then watch the second video. Same thing, the bird follows the exact path and shape of the shadow, because it is the shadow.