Sonograms (top graphs) and oscillograms (bottom graphs) of representative advertisement calls of Ptenopus species (A–J, species names indicated on graphs). Both x and y axes are directly comparable / equally scaled across species. Specimen numbers and localities: A NMNW R11585, NE of Koës, Hardap Region, Namibia; B iNaturalist 140169978 (Jacobus Retief), Merweville, Western Cape Province, South Africa; C NMNW R11622, E of Lüderitz, ||Karas Region, Namibia; D NMNW R11643, SW of Gobabeb, Erongo Region, Namibia; E NMNW R11657, NE of Keetmanshoop, ||Karas Region, Namibia; F NMNW R11704, Gobabeb; G NMNW R11716, Hoanib River, Kunene Region, Namibia; H NMNW R12114, Gobabeb; I NMNW R11843, NW of Gobabeb; J NMNW R11790, N of Swakopmund, Erongo Region, Namibia. The audio files on which this figure is based, are made available (File S2).