Silbo Gomero, also known as el silbo, 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 its loud nature, Silbo Gomero is generally used in circumstances of public communication. Messages conveyed could range from event invitations to public information advisories. A speaker of Silbo Gomero is sometimes referred to in Spanish as a silbador ('whistler'). Silbo Gomero is a transposition of Spanish from speech to whistling. This oral phoneme-whistled phoneme substitution emulates Spanish phonology through a reduced set of whistled phonemes. It was declared as a Masterpiece of the Oral and Intangible Heritage of Humanity by UNESCO in 2009.