Whistle talk

We've always communicated with whistles here. If one person's indoors and another outdoors or if one person's upstairs and another downstairs, it's far more efficient than shouting. Patients communicate with their dentists via mmmm-mmmm talk (rhythm and just a hint of vowel sounds, all hindered by apparatus in the mouth) and dentists usually understand it. With the tidal wave of property flips, sales caused by high property taxes, demolitions, additions, and general repair and remodeling, there's a proportionate increase in the number of surveyors working, from quite early in the morning until last light in the evening. Many of them seem to communicate via whistling (rising tones, falling tones, and more). They always appear to be in a rush or otherwise too busy to quiz, but I'd like to know the secret. Is this customary? If so, do crews follow a communication system in use beyond their working group? Or does each crew develop its own? All the people I could go straight to and ask have left this earthly plane of existence and either I'm using the wrong search terms or there's not much out there to be found in WWW-world. I'd really like to know. Some people train their dogs to respond to various whistles when arm signals are of no use because dog and person are too far apart or otherwise cannot be seen by one another. Some of the Austin solid-waste teams have a whistle system. Truck-drivers and assistants sometimes communicate via whistle when backing up or negotiating a tight spot. I know that the old rail steam whistles were used as a communications system, and I've found at least one military use. Of course, all these systems require whistlers who produce loud and clear sounds.