Dear Marmam members, On behalf of my coauthors I am pleased to announce that we have recently published an article on the energetic cost of toothed whale communicative sound production in The Journal of Experimental Biology. We show that whistling adds no measurable energetic cost in bottlenose dolphins, and that costs are significantly lower than previously reported experimental estimates. The full reference and abstract are found below: Pedersen, M. B., Fahlman, A., Borque-Espinosa, A., Madsen, P. T. & Jensen, F. H. Whistling is metabolically cheap for communicating bottlenose dolphins (Tursiops truncatus). J. Exp. Biol. (2020). Abstract Toothed whales depend on sound for communication and foraging, making them potentially vulnerable to acoustic masking from increasing anthropogenic noise. Masking effects may be ameliorated by higher amplitudes or rates of calling, but such acoustic compensation mechanisms may incur energetic costs if sound production is expensive. The costs of whistling in bottlenose dolphins (Tursiops truncatus) have been reported to be much higher (20% of resting metabolic rate, RMR) than theoretical predictions (0.5–1% of RMR). Here, we address this dichotomy by measuring the change in the resting O2 consumption rate (V̇O2), a proxy for RMR, in three post-absorptive bottlenose dolphins during whistling and silent trials, concurrent with simultaneous measurement of acoustic output using a calibrated hydrophone array. The experimental protocol consisted of a 2-min baseline period to establish RMR, followed by a 2-min voluntary resting surface apnea, with or without whistling as cued by the trainers, and then a 5-min resting period to measure recovery costs. Daily fluctuations in V̇O2 were accounted for by subtracting the baseline RMR from the recovery costs to estimate the cost of apnea with and without whistles relative to RMR. Analysis of 52 sessions containing 1162 whistles showed that whistling did not increase metabolic cost (P>0.1, +4.2±6.9%) as compared with control trials (−0.5±5.9%; means±s.e.m.). Thus, we reject the hypothesis that whistling is costly for bottlenose dolphins, and conclude that vocal adjustments such as the Lombard response to noise do not represent large direct energetic costs for communicating toothed whales. This paper is accessible online at: https://jeb.biologists.org/content/223/1/jeb212498 If you do not have access to JEB, please do not hesitate to contact me for a copy at micbjerre@hotmail.com<mailto:micbjerre@hotmail.com> Best, Michael Pedersen