The Guarani people live in Paraguay, southern Brazil, parts of Argentina, Uruguay and Bolivia. Their demographic dominance has been greatly reduced by European colonization that happened in 16th century (they were 400.000 at this time and are now 30.000). Now, they've got more and more westernalized, and have been despoiled of their territories by deforestation in order to implant soy culture and cattle ranches. They are killed by the farmers, and hundreds of them commited suicide during last years. Their survival is a matter of time.
The birds have always had a great importance in their life, myths and shamanic practices (you can read some examples here). That's the reason the movie dedicated to them was called The Birdwatchers.
I found one of their nose flutes. It certainly is not an ancient one, but it is authentically made by the Guaranis. It is very roughly made, is not my best nose flute (!) but it works, although probably "bird-calling oriented", and not "opera-performance dedicated to".
If you want to support the Guarani's struggle for existence, you can donate here.
Here is a video showing Guarani's "home"-made instruments, but no nose flutes (and others here) :