A bird in this work is a metaphor for relative freedom.
This relates to our mythic structures in that taken literally they can be our captors. Language is a feeble attempt to describe something outside of our understanding and dimensional space.
As in Illuminated Manuscripts, these mythic structures are preserved. It is in the act of writing the stories down that codifies and gives an appearance of permanence. It slows down that rate of change. What is important to note is that these stories get codified in the context in which they were written.
As Joseph Campbell has described, these Myths are beautiful stories that are meant to be understood as a metaphor for ones experience in the world. They are different perceptions of the same phenomena.
Taken literally these myths are “captured” by words and thus can be dangerous. It is for fear of change that stories are written, fear of a loss of tradition. One is captured in the sense that their story is the only story that matters. These are birds in cages.