[[WMG: The bird looks insanely ridiculous for a reason]]
In its original form, capable of traveling through outer space, it was an energy being (with traces of anti-matter) that moved like an earth bird in some capacity, or perhaps its intelligence saw that as a somewhat familiar pattern. It basically formed this pattern or possessed an existing bird (maybe even a true buzzard) and thought it might blend in or not be seen as odd. But it was too alien, and the form was giant and malformed, and looked utterly wrong. The reason the characters in-story didn't see how ridiculous it was, and how much it resembled a badly made puppet was simple : Terror. However it looked to the viewer, it was a temporarily invincible destroying and eating machine - the size of a battleship.