A shepherd’s whistle is traditionally used for communicating comands to sheepdogs. They are typically seen used at sheepdog trials
Shepherd’s whistles are used to communicate clearly and at distances up to several hundred yards the commands of the owner to his working dog. They produce clear, high-frequency tones of an easily modulated and variable pitch, allowing the shepherd to communicate a variety of commands. The pitch is at an optimal frequency for the herding dog’s hearing, and for penetration and distance to cut through adverse weather when gathering sheep.