Silbo Gomero also known as el silbo (‘the whistle’), is a whistled register of Spanish used by inhabitants of La Gomera in the Canary Islands to communicate across the deep ravines and narrow valleys that radiate through the island. It enables messages to be exchanged over a distance of up to 5 kilometres. Due to this loud nature, Silbo Gomero is generally used in circumstances of public communication. Messages conveyed could range from event invitations to public information advisories.
Source: Ultra Facts