Do birds differentiate white noise and deterministic chaos? A playback experiment.

Abstract

Evocative sounds are known to elicit heightened responses from receivers across animal taxa. Many species of caregivers specifically have been shown to have increased arousal from infant baboon screams providing a unique conspecific identification for baboon mothers to discriminate their young from nearby infants (Rendall et al. 2009) to women decreasing their parasympathetic drive after exposure to infants crying, impelling them to react and care for the infants (Tkaczyszyn et al. 2012) to infant giant pandas (Ailuropoda melaneuca). Despite them being relatively common, the function of these nonlinearities is less well-understood. One hypothesis suggests that non-linearities function to increase fear and arousal in receivers (Blumstein and Recapet 2009; Slaughter et al., 2013). Playback experiments have been very useful in evaluation of this nonlinearity and fear hypothesis. In them, investigators have used white noise as a substitute for deterministic chaos. Determinstic chaos contains irregular oscillations with patterns of energy that are irregular and widely distributed over frequency bands (Beckers and Cate 2006). In acoustic spectographs, chaos and noise appear superficially similar, but structurally they are different. We designed two experiments to clarify whether American robins (Turdus migratorius) and warbling vireos (Vireo gilvus) discriminate between white noise and deterministic chaos. Playback experiments consisted of broadcasting one of four types of stimuli at a time to a relaxed bird: white noise or deterministic chaos created from either logistic wave form or a Chua oscillator, and one control stimulus, one of four exemplars of Tropical Kingbird (Tyrannus melancholicus) vocalizations. Robins engaged in significantly less relaxed behavior after hearing noise compared to the kingbird treatment, and all noise/non-linearity treatments led to significantly less relaxed behavior than the kingbird treatment (pair-wise comparisons between kingbird and chua chaos. Pairwise comparisons did show that after hearing chua chaos, warbling vireos decreased locomotion significantly compared to kingbird. Our results suggest that American robins and Warbling vireos do not discriminate noise from at least two types of deterministic chaos: chua chaos and logistic chaos, thus indicating that future playback studies can continue to use white noise as a nonlinear stimulus. 3

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