Elemans, Coen PH, Weili Jiang, Mikkel H. Jensen, Helena Pichler, Bo R. Mussman, Jacob Nattestad, Magnus Wahlberg, Xudong Zheng, Qian Xue, and W. Tecumseh Fitch. “Evolutionary novelties underlie sound production in baleen whales.” Nature (2024): 1-7.
Whales are one of the few non-human animals with something like language. To make their calls, whales face the unique challenge of vocalizing underwater. Communicating underwater is fundamentally different from communicating on land because sound travels differently through water and air. As ancestral whales transitioned from the land to the sea, they evolved adaptations for an aquatic lifestyle, including the ability to breathe huge volumes of air at the surface and avoid choking on water. Mammals use the same structure for both breathing and making sound—the larynx, or voice box—meaning this structure faces unique constraints underwater.
There are two types of whales: toothed whales (such as sperm whales) and baleen whales (like blue whales and humpbacks). The two groups evolved different solutions to communicate underwater. Toothed whales have a special vocal organ in their nose and do not use their larynx to produce sound. Baleen whales, however, have a larynx that is still involved in both breathing and sound production. This larynx has an unusual structure, and until recently scientists did not know how it could produce sounds.
Good vibrations
Recently, scientists studied the larynxes of three different species of baleen whales – sei, minke, and humpback whales. The scientists used a technique called CT scanning, which stands for “computed tomography.” This is the same technology doctors use to image internal anatomy and detect medical problems. The whale researchers used a device to pump air into the larynxes, testing whether and how they produce sound. They found that sounds were produced by air vibrating structures within the larynx that are not found in other mammals—in other words, baleen whales have a totally unique way of vocalizing.
The physical properties of the larynx determine the range of sound frequencies it can produce. The structures identified in the lab produce low-frequency sounds that match the lower range of frequencies produced by living whales. Other muscles and behaviors probably allow whales to produce a wider range of sounds in nature.
There is also variation among species. Some whales, such as humpbacks, seem to have special vocal folds that allow them to produce extremely high-frequency sounds. This mechanism may be important for social communication. High-frequency sounds are more “private” than low-frequency sounds because high-frequency sounds don’t travel as far, and thus social communication often specifically uses higher frequencies.
Can you turn the music down?
The anatomy of the larynx also places a hard physical limit on the depths at which whales can communicate. It takes a certain volume of air to produce sound, and therefore it impossible to vocalize below about 100 meters. Thus, whale vocalizations are limited to shallow waters.
This is a problem because of ship noise. The surface of the ocean is now extremely noisy because of human-made noise from ship traffic and construction. These sounds are often very loud and travel far underwater, making it hard for whales to hear one another. Unfortunately, this study shows that whales can’t simply dive deeper to escape human noises; instead, we will have to find ways to reduce our noise to avoid harming sea creatures.
Cover image source: Christin Khan via Wikimedia Commons
I am a PhD student at MIT and the Woods Hole Oceanographic Institution, where I study the evolution and physiology of marine invertebrates. I usually work with zooplankton and sea anemones, and I am especially interested in circadian rhythms of these animals. Outside work, I love to play trumpet, listen to music, and watch hockey.
