We have one last metaphor for you to check out here. It's not a huge deal, but it's definitely part of the wordplay in this poem. The song of the bird isn't really a crystal stream. The speaker is subtly comparing music to something you can see, a little sparkling stream of water.
Line 85: Everywhere in this poem the speaker blurs the lines between our senses, between what we see, hear, smell, and feel. It creates a beautiful, exciting, but maybe also overwhelming world of feeling, which helps us to understand exactly how much this bird means to our speaker.