The Sound of Arousal: The Addition of Novel Non-linearities Increases Responsiveness in Marmot Alarm Calls

Much attention has focused on tonal and harmonic sounds that animals produce, while less attention has focused on the production or function of atonal, non-harmonic sounds, despite these non-linear vocal phenomena being easily identified on a spectrogram (Fitch et al. 2002). Formally, only pure tones have no non-linear attributes because harmonics are one type of non-linearity. In this study, we focus on other types of non-linearities because they have received relatively less study. They include (but are not limited to Wilden et al. 1998; Fitch et al. 2002): subharmonics (additional tonal components below the fundamental frequency), biphonation (the production of a second fundamental frequency), deterministic chaos (broadband components of low dimensional or non-random noise), and noise (broadband hissing, whispering, or white noise). In addition, bifurcations (and to a lesser extent warbles) are abrupt frequency changes caused by a sudden change in the vibrations of the vocal folds and are broadly included in the class of non-linear vocal phenomena. Indeed, these non-linear phenomena are a common feature of vocalizations in more than 30 mammals (Wilden et al. 1998; Tokuda et al. 2002; Facchini et al. 2003; Riede et al. 2004; Mann et al. 2006; Tyson 2006; Volodina et al. 2006; Tyson et al. 2007), birds (Fee et al. 1998; Beckers & ten Cate 2006), and amphibians (Suthers et al. 2006). Correspondence Daniel T. Blumstein, Department of Ecology & Evolutionary Biology, University of California, 621 Young Drive South, Los Angeles, CA 90095-1606, USA. E-mail: [email protected]