The gwythaint fledgling was a wounded baby bird, rescued by Taran of Caer Dallben.
While traveling in the Eagle Mountains, Taran found the fledgling in a bush and nursed it back to health. Doli of the Fair Folk begrudgingly made a cage for it. Even while recuperating the gwythaint was watchful, and seemed to sense the intentions of the Companions, refusing to allow Fflewddur Fflam (who had voted to kill it) to touch it, while accepting Taran's stroking finger.
The fledgling gwythaint soon escaped its cage, just as Doli said he would, and vanished. Yet despite the dwarf's dire warnings of its treachery, the gwythaint led Gwydion to Taran and enabled the undoing of the Horned King near Caer Dathyl.
How the gwythaint received its wounds, and how it knew of Gwydion's relationship to Taran remain unknown.Mount Dragon to his death. It then repaid its debt in full by flinging itself against the Cauldron-Born, in an effort to buy Taran the time