This is the sound of Silbo Gomero, or “Gomeran Whistle.” According to agulo.net, “speakers” of this whistled language understand it basically as a Spanish conversation that goes:

¡Servando¡, ¿qué?, mira, dile a julio que vaya y que traiga las chácaras. Ya voy ¡ julio! ¿qué? Que dice lilí que avises a los muchachos y que traigan las chácaras para la fiesta bueno, bueno, bueno

which means:

something about “bring the Chácaras”

I first learned about Silbo in the fantastic Proceedings of the Athanius Kircher Society: “Silbo, the whistling language of Gomero Island has a vocabulary of over 4,000 words.” Thanks to Praat, we can see the subtle intonations that encode meaning:
[singlepic=27,300,,web20,]
See and hear more:

[youtube]http://www.youtube.com/watch?v=qlZh9I1pxj0[/youtube]

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