Subharmonics increase the auditory impact of female koala rejection calls

Abstract

Although non‐linear phenomena are common in human and non‐human animal vocalisations, their functional relevance remains poorly understood. One theory posits that non‐linear phenomena generate unpredictability in vocalisations, which increases the auditory impact of vocal signals, and makes animals less likely to habituate to call repetition. Female koalas (Phascolarctos cinereus) produce vocal signals when they reject male copulation attempts that contain relatively high levels of non‐linear phenomena, and thus may function as attention grabbing vocal signals during the breeding season. To test this hypothesis, we used playback experiments: firstly, to determine whether female rejection calls induce heightened behavioural responses in free‐ranging male koalas during the breeding season, and secondly, to examine how the relative amount of non‐linear phenomena in rejection calls influences male behavioural response. The results show that male koalas look for longer towards speakers broadcasting playback sequences of male bellows followed by a series of female rejection calls than those broadcasting only male bellows. In addition, female rejection call sequences with more subharmonics, higher harmonics‐to‐noise ratios, and less biphonation produced the greatest male looking responses. Our findings support the hypothesis that female koala rejection calls function to grab male attention during the breeding season, and indicate that subharmonics are the main acoustic feature that increases the auditory impact of these vocal signals.

Vocal behaviour predicts mating success in giant pandas

“…Alternatively, increased F0 could reflect an attempt to produce a more conspicuous signal to draw attention to the caller, perhaps to encourage male sexual attention. In addition, a higher incidence of nonlinear phenomena in female chirps is likely to increase the auditory impact of these calls [ 48 , 49 ] and recent studies of mammal vocal communication have shown that vocalizations with nonlinear phenomena are particularly evocative and hard to ignore [ 50 – 52 ]. Accordingly, we suggest that the relatively high F0 and greater incidence of nonlinear phenomena in chirps produced during unsuccessful breeding introductions reflects an attempt by females to grab and maintain the attention of male receivers that may be reluctant to mate.…”

Do birds differentiate between white noise and deterministic chaos?

“…Evidence indicates these phenomena might serve adaptive functions (Morton ; Fitch et al., ). For example, vocalizations with nonlinearities may allow listeners to better differentiate between individuals of the same species (Rendall, Notman, & Owren, ) and, in particular, subharmonics may alter the way listeners behave around the communicating individual by indicating size or dominance (Fitch et al., ; Morton, ), or caller arousal levels (Charlton et al., ). Also, calls containing noise or rapid jumps in frequency from tonal sound to noise may be more difficult to habituate to and function to get receivers’ attention (Blumstein & Recapet, ; Townsend & Manser, ).…”

“…Noisy screams, cries, and other sounds often contain specific structural characteristics that are particularly evocative to listeners. These nonlinear acoustic phenomena are found in vocalizations from a variety of taxa including terrestrial mammals (Blumstein, Richardson, Cooley, Winternitz, & Daniel, 2008;Charlton, 2015;Charlton, Watchorn, & Whisson, 2017;Rendall et al 2009;Riede, Arcadi, & Owren, 2007;Stoeger, Baotic, Li, & Charlton, 2012;Stoeger, Charlton, Kratochvil, & Fitch, 2011;Tokuda, Riede, Neubauer, Owren, & Herzel, 2002;Wilden, Herzel, Peters, & Tembrock, 1998), marine mammals (Tyson, Nowacek, & Miller, 2007), frogs (Pettitt, Bourne, & Bee, 2012), toadfish (Rice, Land, & Bass, 2011), and birds (Fee, Shraiman, Pesaran, & Mitra, 1998).…”

“…Recently, Charlton et al (2017) found that subharmonics in koala (Phascolarctos cinereus) female rejection calls increased their auditory impact in a playback experiment with male koalas. Further, nonlinear phenomena present in film soundtracks have been used to elicit fearful responses in humans (Blumstein, Davitian, & Kaye, 2010).…”

Excised larynx experimentation: history, current developments, and prospects for bioacoustic research

“…Some work has evaluated the functional relevance of NLP in bioacoustic research, with potential purposes such as preventing habituation, inducing perceptual changes, indicating status, individuality, motivation, and physical health (Wilden et al, 1998;Fitch et al, 2002). Exploring this avenue, studies have shown that NLP may indeed indicate physical condition (Riede et al, 2007), arousal state (Blumstein et al, 2008;Garcia et al, 2014), individuality (Volodina et al, 2006), or drawing increased conspecifics attention (Blumstein and Récapet, 2009;Townsend and Manser, 2011;Reby and Charlton, 2012;Charlton et al, 2017). Nevertheless, the connection between the potential function and the production mechanisms associated with NLP has not been investigated to date.…”