http://www.slate.com/articles/video/video/2015/08/turkey_whistle_language_video_how_whistled_turkish_works_in_the_brain_video.html

In the northeastern mountains of Turkey, residents separated by tree-packed slopes turned to an unusual communication method: whistling. Small villages adapted the language, known as whistled Turkish—which, as it sounds, is Turkish adapted into a series of whistles—as a means for long-distance communication long before the telephone or Twitter was an option.