Meeting Abstract
The ability to distinguish fundamental frequency from resonant frequency in vertebrates with tubular vocal tracts essentially eliminated dominant frequency as a proxy for resonant frequency in birds and mammals. Many studies have since shown that fundamental frequency and resonant frequency convey important different information to signal receivers. Anurans lack a tubular vocal tract, making this differentiation difficult. Thus, anuran call analysis still relies on dominant frequency. Interestingly, intensity modulation of dominant frequency in anurans is common, for example, in Fowler’s Toads (Anaxyrus fowerli). While physiological hypotheses abound, we propose a biomechanical association with small body size as another explanation of intensity modulation. We analyzed male advertisement calls to disambiguate fundamental and resonance frequencies of A. fowleri. The observed shift in fundamental frequency helped to identify resonant frequency. Since the fundamental frequency was also heavily amplitude-modulated, intensity changes of the upper and lower sidebands were used to completely scan the entire resonance. Using a Helmholtz model, the resonant frequency and quality factor were extracted. A. fowleri exhibited distinct fundamental and resonant frequencies whose close proximity contributed to low spectral flatness. A comparison of mainland versus dwarf island toads suggest that resonant frequency is inversely correlated with head width and that fundamental frequency is inversely correlated with snout-vent length. These previously undetected characteristics of advertisement calls impact the interpretation of intensity modulation in anurans as static versus dynamic call trait.
