Birds are a universal symbol of freedom. However, throughout literature they have typically been depicted as fragile or delicate and associated with women. Here, the “littleness” of the bird suggests that this creature is being persecuted in some way. It immediately makes readers sympathize with this frail creature, creating a helpless tone that should cause outrage at the speaker's plight.
The now-archaic pronoun “naught” simply means “nothing.” The little bird, trapped in a cage, has only one thing that it can do: sing. Beginning the second stanza with this word indicates the boredom and despair that the captive feels as she resigns herself to performing the only action that she can in the cage.
