This paper describes the methods used to study the tone and some related phenomena of the language of the Gavião of Rondônia, Brazil, which is part of the Mondé branch of the Tupi family. Whistling of words by indigenous informants was discovered to be a very effective method for obtaining phonetic accuracy in tone and length. Methods were devised to map out the system of tone and length. They were subsequently used in the study of other Amazonian languages, including Karitiana, Munduruku, Zoró, and Surui of Rondônia, with success. Some notes on tone considerations in orthography are offered, as well as notes on procedures that proved useful in the diachronic study of tone in the Mondé languages. Methods for the study of natural whistled speech used for distance communication are also described, with special attention to the whistled speech of the Gavião, including its use, its efficiency, and the whistling techniques used. The relation between some aspects of Gavião instrumental music and the suprasegmental aspects of the language are also discussed and the methods used to study this are described. Audio and video clips illustrate the phenomena being discussed.