take a ferry from the mainland to the island of evia. pass giant wind farms and a hidden waterfall, then you ( whistling ) encounter the unique voice of kyriaki giannakari, trilling as clear as a bird, chatting to her distant neighbors. ( whistling ) >> ( translated ): it's essential we preserve this language. we have to keep it. this is the way we've grown up. this is our heritage. ( whistling ) >> reporter: and this is how they invite their friends to lunch. using a technique that distinctly transmits the message for miles between hill tops. eperts believe the language dates back to ancient greek times. one theory is that it was created by persians 2,500 years ago after they were defeated in the great naval battle of salamis. survivors washed up on the shores of evia whistled to each other to avoid detection from vengeful ancient greeks. panagiotis tzanavaris is leading the battle to save what unesco considers to be the world's most endangered language. >> ( translated ): whistling was used widely used until the day the telephone arriv