Caterbirds were mystical birds which hatched roughly once every hundred years from cocoons woven by Glisters. Caterbirds were capable of speech, and were highly intelligent. Because all Caterbirds could share dreams with all others, Caterbirds typically regarded themselves as all the same individual, as opposed to a species of creatures. Anyone who slept inside an empty Caterbird cocoon would experience dreams and memories experienced by previous Caterbirds, and anyone present at a Caterbird's hatching would be blessed with the protection of that particular Caterbird for as long as they lived. Twig witnessed the hatching of a Caterbird once, and it saved his life on numerous occasions, despite an occasional reluctance to do so.
The Caterbird was the third of the three Ancient Ones, the one who ruled the Sky.