Vocal performance affects metabolic rate in dolphins: implications for animals communicating in noisy environments

Abstract

Many animals produce louder, longer or more repetitious vocalizations to compensate for increases in environmental noise. Biological costs of increased vocal effort in response to noise, including energetic costs, remain empirically undefined in many taxa, particularly in marine mammals that rely on sound for fundamental biological functions in increasingly noisy habitats. For this investigation, we tested the hypothesis that an increase in vocal effort would result in an energetic cost to the signaler by experimentally measuring oxygen consumption during rest and a 2 min vocal period in dolphins that were trained to vary vocal loudness across trials. Vocal effort was quantified as the total acoustic energy of sounds produced. Metabolic rates during the vocal period were, on average, 1.2 and 1.5 times resting metabolic rate (RMR) in dolphin A and B, respectively. As vocal effort increased, we found that there was a significant increase in metabolic rate over RMR during the 2 min following sound production in both dolphins, and in total oxygen consumption (metabolic cost of sound production plus recovery costs) in the dolphin that showed a wider range of vocal effort across trials. Increases in vocal effort, as a consequence of increases in vocal amplitude, repetition rate and/or duration, are consistent with behavioral responses to noise in free-ranging animals. Here, we empirically demonstrate for the first time in a marine mammal, that these vocal modifications can have an energetic impact at the individual level and, importantly, these data provide a mechanistic foundation for evaluating biological consequences of vocal modification in noise-polluted habitats.

Changes in bottlenose dolphin whistle parameters related to vessel presence, surface behaviour and group composition

“…This study suggests that the acoustic parameters of whistle vocalizations vary naturally according to behavioural context and group composition, but are also influenced by tour boat presence and engine noise. The vocalization changes we observed in the presence of one or more tour boats could have a long-term, negative influence on the bottlenose dolphin population in Walvis Bay if they reduce the communication range of whistles (Jensen et al, 2009), result in increased energy expenditure (Holt, Noren, Dunkin, & Williams, 2015;Williams et al, 2006) or elevate stress levels (Rolland et al, 2012;Romano et al, 2004). Such effects would be compounded if combined with other behavioural responses to tour boat presence that increase energy expenditure, for example increased socializing or travelling (Indurkhya, 2012).…”

“…As we could not measure whistle source levels, it was not possible for us to determine whether the shifts in frequency we observed were accompanied by amplitude modifications. Previous studies investigating the Lombard effect in cetaceans did not investigate concurrent changes in signal frequency (Holt et al, 2009;Scheifele et al, 2005) or failed to demonstrate a frequency shift associated with increased amplitude (Holt et al, 2015;Parks et al, 2011). However, as this research area is in its infancy, a possible coupling between the Lombard effect and other noise-induced vocal modifications in cetaceans warrants further investigation (Hotchkin & Parks, 2013).…”

Cook Inlet beluga whale, Delphinapterus leucas, observations near Anchorage between 2008 and 2011: results from a citizen scientist project

“…Many animals produce louder, longer, or more repetitious vocalizations to compensate for increases in environmental noise (Parks et al, 2011;Holt et al, 2015). Further, Holt et al (2015) found that an increase in vocal effort between captive common bottlenose dolphins, Tursiops truncatus, created an increase in metabolic rate and oxygen consumption over a resting period that followed sound production in both animals, and that the metabolic cost may add up over time when the individuals must compensate for chronic background noise.…”

“…Further, Holt et al (2015) found that an increase in vocal effort between captive common bottlenose dolphins, Tursiops truncatus, created an increase in metabolic rate and oxygen consumption over a resting period that followed sound production in both animals, and that the metabolic cost may add up over time when the individuals must compensate for chronic background noise. A similar metabolic effect may be of concern for Cook Inlet belugas, particularly with an increase in ambient noise levels due to increases in shipping and construction activity.…”

Impacts of Navy Sonar on Whales and Dolphins: Now beyond a Smoking Gun?

“…Williams et al (2017) reported a theoretical 30.5% increase in beaked whale metabolic rate, with an elevated rate being maintained for more than 90 min after the exposure to noise. Even increasing the amplitude of vocalizations-so that calls may be heard in a noisy environment-may have an energetic cost (Holt et al, 2015).…”