On the island of La Gomera in the Canary Islands, the native Guanches who lived there long before the Spanish conquest had a whistled language. The sound of whistling carries much farther than spoken language, so whistling allowed communication across La Gomera’s steep ravines and thick forests. The spoken language has since died out, but the residents of La Gomera have kept the whistling tradition, which they call Silbo Gomero, alive. The language has four vowels and four consonants, and it’s even taught in the schools.
Andrew Bird, eat your heart out.
[Edited 2/3: Changed the video out for a shorter and more informative one.]