Peoples of the Vaupes and the upper Rio Negro, in what is now the border country of Colombia and Brazil, keep sets of paired wind instruments that are restricted. They are not kept in the settlement. Access to them is limited to men who have been initiated, and they are central to that initiation. Those facts are established in the published record and are not in dispute.
Beyond that, this entry stops, and the stopping is deliberate. It does not describe the rite. It does not set out how the instruments are made, what they are named, what is said or sung with them, or what happens to someone who encounters them without standing. Those are the parts the communities concerned restrict, and a restriction does not lapse because a book was published.
Two further points belong here. First, Yurupari is not any of these peoples' word for what they have. It comes from the Amazonian lingua geral and was adopted by outsiders as a convenient cover term for practices that differ substantially between Tukanoan and Arawakan groups, so the label itself flattens the thing it names. Second, the atlas holds no specialist ethnography of the Vaupes among its sources. That gap is recorded as an open question rather than filled with general reference material, because a subject like this one is precisely where a thin source produces a confident and wrong description.