Resonance plays a secondary role in amplifying underwater vocalizations of Weddell seals (Leptonychotes weddellii)

Abstract

AbstractDuring the breeding season, male Weddell seals (Leptonychotes weddellii) defend underwater territories using high amplitude trill vocalizations (some >190 dB re 1 μPa‐m). The source‐filter theory states that the characteristics of vocalizations are a product of both the sound produced at the source and the effects of soundwave reflection within the vocal tract. This study aimed to determine the relative influence of reflection (resonance). Weddell seal trills (tonal descending frequency sweeps ranging from >20 to <0.1 kHz) offered a unique opportunity to look for resonance in the spectral patterns, appearing as periodic peaks in amplitude over short frequency intervals. Additionally, distributions of frequencies with absolute maximum amplitude (FMA) were tested against random distributions to look for frequencies where FMAs occur more frequently than by chance. All methods exhibited evidence of resonance at 0.45–0.56 and 2.25–2.83 kHz. These frequencies would resonate in closed‐at‐both‐ends tubes with lengths of 32–40 and 6–8 cm, respectively. These lengths approximate the likely sizes of the trachea and larynx or pharynx respectively. The amplitudes of the underwater calls of Weddell seals primarily result from the amplitude generated by the sound source in the larynx with some additional amplitude associated with resonance in the vocal tract.