Silbo Gomero: A Language That Consists Entirely Of Whistling 

Silbo Gomero is the language spoken on the island of La Gomera, in the Canary Islands of Spain, and is made entirely from whistled sounds. It evolved to allow fast public communication across distances of over 5km across the narrow valleys and deep ravines that permeate the island.

https://weird-history-facts.com/silbo-gomero-whistling-language/