I just read about this language today. It consists of 2 vowels, 4 consonants and over 4000 words, all communicated by whistles. The whistles stimulated the portions of the left brain involved in language production and comprehension in those who "spoke" Silbo, but not in those who didn't "speak" the language. Here's a UW article and a Wikipedia article about it.

Tinman

Wow! That is so cool! I must learn this! Thanks so much for the articles, Tinny. I have a friend who always whistles and says things in his whistles, but I never had any idea there was a real language somewhere. I can't wait to call and tell him!

I am reviving a 2005 post about Silbo Gomero by Tinman because someone sent me this link today. It sounds like a great idea for those places that don't have Internet accessibility.