In the rugged cloud forests of northern Oaxaca, Mexico, the Chinantecan people communicate in one of the world's most unusual languages—not by speaking, but by whistling.

In the clip below, spotted by Open Culture, Dr. Mark Sicoli of Georgetown University and David Yetman of the University of Arizona visit the region as part of an episode for PBS's In the Americas with David Yetman. Their quest is to find out how many people still speak (or rather, whistle) the tongue, which is used to communicate across the hills and valleys of the mountainous terrain. Along the way, they discover how the language has been involved in the community's rites of passage, town meetings, gender norms, and cornfields. They also get a beaming crowd of schoolchildren to whistle "I'm tired," and witness a whistled conversation about a taco. Perhaps not surprisingly, the language is in danger of dying out—unless the youngest generation can save it.

As special as the language is, the Chinantecan whistlers of Oaxaca aren't alone: 42 examples of whistled human tongues have been documented, in the Amazon, Turkey, Greece, and the Canary Islands, to name just a few spots. The languages are usually found in places with high slopes or thick forests, where regular spoken communication is tricky. Whistling, it turns out, isn't just for the birds.

[h/t Open Culture]