Whistled Turkish is exactly what it sounds like: Turkish that has been adapted into a series of whistles.
This method of communicating was popular in the old days, before the advent of telephones, in small villages in Turkey as a means for long-distance communication.
In comparison to spoken Turkish, whistled Turkish carries much farther.
While whistled-Turkish speakers use "normal" Turkish at close range, they switch to the whistled form when at a distance.