Brief report: Occurrence of anti‐resonance in the song of the siamang (Hylobates syndactylus)

The duetting behavior of siamangs (Hylobates syndactylus) has previously been observed as representing a complex, interactively organized, and standardized set of vocal features. Anti-resonance in the bitonal screams of 15 males was observed. The sound energy of the fundamental frequency of the first note of these screams are absorbed, the result being a fundamental frequency which was virtually filtered out. The implications and consequences of such a rare phenomenon as anti-resonance in the vocal behavior in gibbons is discussed.