The verb “to bend” also means to tie, fetter, or otherwise restrain. This meaning of the word suggests that the man deliberately restrains her in order to hear her song. While birdsong usually has positive connotations that symbolize freedom, joy, and peace, the “bending” in this line changes the connotations of the song. It becomes a symbol of her oppression rather than her freedom; He repurposes it for His own means. In this way, He not only metaphorically destroys her freedom but literally takes it from her.
The metaphor “fields of air” portrays the air as if it were part of the land. This metaphor suggests that while the speaker identifies with a bird, she is a human who would feel freedom in wide-open land spaces.
