Birds began singing in brake and copse: birds were faithful to their mates; birds were emblems of love.
– Charlotte Bronte
Jane Eyre, Chapter 27. Jane begins to question who she is and how her love compares to that of the birds. Faithful to their partners, birds are seen by her as emblems of love (metaphor). She envies them because they are happy in a way that she cannot be with the married Rochester.