title: Biomechanical control of vocal plasticity in an echolocating bat.
abstract: Many animal species adjust the spectral composition of their acoustic signals to variable environments. However, the physiological foundation of such spectral plasticity is often unclear. The source-filter theory of sound production, initially established for human speech, applies to vocalizations in birds and mammals. According to this theory, adjusting the spectral structure of vocalizations could be achieved by modifying either the laryngeal/syringeal source signal or the vocal tract, which filters the source signal. Here, we show that in pale spear-nosed bats, spectral plasticity induced by moderate level background noise is dominated by the vocal tract rather than the laryngeal source signal. Specifically, we found that with increasing background noise levels, bats consistently decreased the spectral centroid of their echolocation calls up to 3.2 kHz, together with other spectral parameters. In contrast, noise-induced changes in fundamental frequency were small (maximally 0.1 kHz) and were inconsistent across individuals. Changes in spectral centroid did not correlate with changes in fundamental frequency, whereas they correlated negatively with changes in call amplitude. Furthermore, while bats consistently increased call amplitude with increasing noise levels (the Lombard effect), increases in call amplitude typically did not lead to increases in fundamental frequency. In summary, our results suggest that at least to a certain degree echolocating bats are capable of adjusting call amplitude, fundamental frequency and spectral parameters independently.
authors.affiliation: Max Planck Institute for Ornithology, Acoustic and Functional Ecology Group, Eberhard-Gwinner-Straße, Seewiesen 82319, Germany Division of Neurobiology, Department Biology II, Ludwig-Maximilians-Universität München, Großhaderner Straße 2, Planegg-Martinsried 82152, Germany luojh135@gmail.com lutzw@lmu.de.
authors.forename: Jinhong
authors.initials: J
authors.lastname: Luo
authors.affiliation: Division of Neurobiology, Department Biology II, Ludwig-Maximilians-Universität München, Großhaderner Straße 2, Planegg-Martinsried 82152, Germany luojh135@gmail.com lutzw@lmu.de.
authors.forename: Lutz
authors.initials: L
authors.lastname: Wiegrebe
mesh_terms: D000161:Acoustic Stimulation; D000162:Acoustics; D000818:Animals; D001696:Biomechanical Phenomena; D002685:Chiroptera / Q000502:physiology*; D004455:Echolocation; D005260:Female; D008297:Male; D013016:Sound; D013018:Sound Spectrography; D014828:Vocalization, Animal / Q000502:physiology*
keywords: Anthropogenic noise; Behavioural flexibility; Instantaneous frequency; Noise pollution; Speech production