Fig. 1. (A) Relationship between body mass and average fundamental frequency (F₀) for non-human primate species [solid line (from Tembrock, 1996); 122 species considered; y=1443x^–0.623] and several mammals, except primates [dotted line (from Fletcher (Fletcher, 2004); unknown number of species considered; y=1403x^–0.409]. (B) Relationship between vocal fold length and average fundamental frequency (y=3537x^–1.214). The regression is based on human vocal fold data and average F₀ in the speaking voice [fig. 7.7 in Titze (Titze, 2000)]. In A and B, the North American elk, European red deer and an average male human are indicated by filled circles.