if not radiation, rats would have survived natural disasters.
i still don't think that 'bird' was a bird. there are other skeletons that are more bird like.
i reckon this ^ one had feathers. flamingo/heron looking. i can see it with feathers and not scaly like in the artists version of what it looks like in google images. large wingspan and beak and short tail. if you took the head off of that and turned it around then put it back on again, the beak would look more in line with those birds i mentioned.