Toothed whales like dolphins, orcas, and sperm whales produce their diverse repertoire of sounds through a distinct structure in the nasal passages, but in a way that is strikingly similar to the way terrestrial animals use the larynx or syrinx for vocalization. In a new study, researchers who employed four different techniques to get to the bottom of how these animals make the sounds they do describe this novel sound production system and show how it enables toothed whales to use different vocal registers for echolocation and communication. To date, vocal registers have been confirmed only in humans and crows. Odontocetes (toothed whales) navigate and hunt prey in deep, dark marine environments using echolocation, a strategy that relies on the producing short, rapid and powerful ultrasonic echolocation clicks, which for some species can approach a blistering 200 decibels in volume – just shy of the loudest sounds ever recorded. In addition, toothed whales can produce an acoustically rich collection of grunts, bursts, and whistles used to compose complex vocalizations used for social communication. While its thought that these sounds are created through an airflow-driven sound source called the phonic lips located in the nose, the mechanisms that enable such complex sound production, particularly at depths hundreds of meters below the surface, remain largely unknown. Using a combination of interdisciplinary methods that past studies have lacked – including in vivo imaging and recording in trained whales, novel in vitro laboratory experiments, and techniques used to study sound variation in the human voice – Peter Madsen and colleagues show that odontocete sounds are produced through the nasal passages in a way that is functionally analogous to laryngeal and syringeal sound production in other terrestrial vertebrates, like humans and birds. According to the authors, where laryngeal sound would be hampered by pressure and minimal respiratory air volume, passing air through the nasal passage allows complex sounds to be generated at depths these animals frequent. Madsen et al. also discovered that toothed whales use different vocal registers, namely vocal fry, chest, and falsetto voice, to generate the fundamentally different tones used for echolocation and vocal communication. In a related Perspective, Andrea Ravignani and Christian Herbst discuss the study in greater detail.
**This paper is related to an Annual Meeting Briefing for Science, titled "Uncovering the voice of toothed whales: a distinct nasal structure helps produce diverse sounds," to be held on March 2nd at 9:00 am US ET. You can access the briefing virtually here if you are registered for the AAAS Annual Meeting. (Please add briefing link to your calendars).
NOTE: If you'd like to attend this and other briefings at the 2023 Annual Meeting and have not yet registered, please do so by March 1st
