The song of the veery is a haunting, ethereal song. Males sing at dusk, a time when not many other birds sing and daytime winds have calmed. It's also a time when the air turns damp; dense, moist air transfers sound waves better than dry air.
If you listen to the song carefully, you can hear an echo or tremolo effect (more on this below), because songbirds have, essentially, a double voice box that can produce two notes at the same time. (The left voice box is lower pitched than the right one.) In a sense, a singing veery harmonizes with itself.