The metabolic cost of communicative sound production in bottlenose dolphins (Tursiops truncatus)

Abstract

SUMMARYBottlenose dolphins (Tursiops truncatus) produce various communicative sounds that are important for social behavior, maintaining group cohesion and coordinating foraging. For example, whistle production increases during disturbances, such as separations of mother-calf pairs and vessel approaches. It is clear that acoustic communication is important to the survival of these marine mammals, yet the metabolic cost of producing whistles and other socials sounds and the energetic consequences of modifying these sounds in response to both natural and anthropogenic disturbance are unknown. We used flow-through respirometry to determine whether the metabolic cost of sound production could be quantified in two captive dolphins producing social sounds (whistles and squawks). On average, we found that metabolic rates measured during 2min periods of sound production were 1.2 times resting values. Up to 7min were required for metabolism to return to resting values following vocal periods. The total metabolic cost (over resting values) of the 2min vocal period plus the required recovery period (163.3 to 2995.9mlO 2 or 3279.6 to 60,166.7J) varied by individual as well as by mean duration of sounds produced within the vocal period. Observed variation in received cumulative sound energy levels of vocalizations was not related to total metabolic costs. Furthermore, our empirical findings did not agree with previous theoretical estimates of the metabolic cost of whistles. This study provides the first empirical data on the metabolic cost of sound production in dolphins, which can be used to estimate metabolic costs of vocal responses to environmental perturbations in wild dolphins.

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

“…for breathhold diving) and sound production mechanisms. Furthermore, recent empirical estimates of the metabolic costs of whistle production in the bottlenose dolphin (Noren et al, 2013) do not agree with previous theoretical estimates based on the acoustic energy of the whistles and assumptions about the efficiency factor of sound production (Jensen et al, 2012).…”

“…Madsen and Surlykke, 2013). However, theoretical predictions of the metabolic cost of acoustic signaling based on the acoustic energy released to the environment are inconsistent with empirical results (Noren et al, 2013). Comparisons of costs between smaller terrestrial endotherms and larger marine dolphins are also complicated by other differences including sound production anatomy.…”

“…We tested this hypothesis by measuring metabolic rates during resting and variable levels of sound production in bottlenose dolphins, T. truncatus (Montagu 1821). The current study differed from the approach of Noren et al (2013) in that the subjects were specifically trained to modify their vocalizations to produce either 'soft' sounds (when the 'soft' training cue was given) or 'loud' sounds (when the 'loud' training cue was given) within a trial, with a goal of 'loud' sounds being +10 dB relative to 'soft' sounds. Changes in vocal effort were then related to changes in metabolic performance across trials.…”

“…The energetic costs of acoustic signals have been well investigated in some vertebrate groups such as amphibians and birds (reviewed in Ophir et al, 2010;Stoddard and Salazar, 2011) while empirical measurements in mammals are more limited (Speakman et al, 1989;Russell et al, 1998). Most recently, Noren et al (2013) found that dolphins vocalizing for a 2 min period have metabolic rates that are 1.2× resting metabolic rate, a similar increase to those found in echolocating bats hanging at rest and many birds producing sound with minimal body movement (Speakman et al, 1989;Franz and Goller, 2003;Ward et al, 2003). Total metabolic cost (over resting values) of sound production by dolphins varies between 163 and 2996 ml O 2 for a 2 min vocal bout and is positively related to the duration of the sounds produced, but these results are based on small sample sizes and the subjects were not specifically trained to vary their vocal effort across trials (Noren et al, 2013).…”

“…Most recently, Noren et al (2013) found that dolphins vocalizing for a 2 min period have metabolic rates that are 1.2× resting metabolic rate, a similar increase to those found in echolocating bats hanging at rest and many birds producing sound with minimal body movement (Speakman et al, 1989;Franz and Goller, 2003;Ward et al, 2003). Total metabolic cost (over resting values) of sound production by dolphins varies between 163 and 2996 ml O 2 for a 2 min vocal bout and is positively related to the duration of the sounds produced, but these results are based on small sample sizes and the subjects were not specifically trained to vary their vocal effort across trials (Noren et al, 2013). Despite these few studies, the metabolic costs specifically associated with changes in vocal effort have remained empirically undefined in most taxa, with the few data limited to those measured in humans and birds (Russell et al, 1998;Oberweger and Goller, 2001;Zollinger et al, 2011).…”