Silbo Gomero is a method of transposing the sounds of spoken Spanish into whistles. Arika Okrent at mental_floss explains:
The human voice can only carry so far, but a whistle can travel for miles. In the mountains and ravines of La Gomera, in the Canary Islands, a language of whistles has been used for centuries to transmit long distance messages with amazing accuracy.
The article goes on to explain that there are other whistle-languages known in other parts of the world.
In Ghanaian folklore, the mmoatia communicate by means of a whistling language, and whistling in the forest is a sure way to get their attention.
In the world of Taylor Smart, many fae are familiar with the language of birds—a detail I added in honor of The Hobbit, although Tolkien no doubt was inspired by Germanic mythology, where this ability comes up from time to time.
It would definitely be a handy skill to have, especially since you can rarely get a cell phone signal in faery-land.