From page 12 of Birds of South America: Passerines:
Have you ever stopped to notice the beauty of birdsong? It turns out birds are built for singing! Birds produce sound in the syrinx (as opposed to the larynx, where humans and other mammals produce sound) located deep in their chests where the trachea splits into two bronchi. Many birds can produce sound in both bronchi, making it possible for them to produce two notes at once. No wonder they have so much range!
This comprehensive field guide to the birds of South America covers all 1,952 passerine species to be found south of Panama, including offshore islands such as Trinidad, the Galapagos, and the Falklands, and the islands of the Scotia Arc leading to the Antarctic mainland. It features 197 stunning color plates and detailed species accounts that describe key identification features, habitat, songs, and calls. All plumages for each species are illustrated, including males, females, and juveniles. This easy-to-use guide is the essential travel companion for experienced birdwatchers and novice birders alike.