Whistled languages are a direct result of surrounding environment. Complementary to their spoken versions, they help humans communicate in the distance overcoming natural barriers without travelling: steep topography, cliffs or dense forests. Landscape-related professions that deal with constant loneliness, such as shepherds, hunters or fishermen, profit from this system to warn the others from dangers, emergencies, wolf attacks or enemy invasions.
There are whistled communication methods in every main family of languages (listen): French Pyrenees, Turkey, Mexico, Greek islands, Amazon forests, North Vietnam Hmong peoples, or desert zones in West Africa. One of them is the Silbo Gomero in Spanish Canary Islands, reported in historical records since 15th century and inscribed on the list of UNESCO Intangible Cultural Heritage of Humanity in 2009.
Since Pre-Hispanic times, whistling was an efficient and economic response to communicating two distant hills without building a bridge. The way in which the message is sent out does not require any vibration from the vocal cords. Having a narrower bandwidth than human voice, whistled sounds manage to travel further (1-5 km) and become less affected by background noise than shouting. It is possible to whistle every oral language, once the system of reduction of vowels and consonants is established. The phonetic characteristics of the spoken language are simply reproduced by a different method. Instead of A-E-I-O-U, there are only two vowels: a high-pitched (for both E and I) and a grave one (for A, O and U). Some authors have proposed that there are four though. All consonants are reduced to two high-pitched and two grave tones.
In La Gomera Island, locals used to speak and whistle Guanche, but with the arrival of Spanish conquistadores, it evolved into whistled Spanish. (Hear a sample conversation with subtitles). The Silbo Gomero is not any code, but an articulated structure that can reproduce any given spoken language. The vocabulary is basically reduced to everyday activities, being much more restricted than its spoken equivalent. Nowadays, it is mainly used to announce weddings and funerals, although it has been implanted in secondary school for islanders.
<It is not a language created for the intimate. It is for the public. It must be said out loud and can be heard by all.>
[more info> highly recommendable post-doc research on whistled languages by Julien Meyer]