Final answer:
Juliet insists that the bird outside is a nightingale when it is actually near daybreak because she is using personification to describe the bird's song. This emphasizes the beauty and romanticism of the moment.
Step-by-step explanation:
Juliet insists that the bird outside is a nightingale when it is actually near daybreak because she is using a poetic device called personification. Personification is when an author gives human qualities or attributes to non-human things. In this case, Juliet is using personification to describe the bird's song that she hears outside as a nightingale's song, even though it may not actually be a nightingale singing. By using this literary device, Juliet is emphasizing the beauty and romanticism of the moment.