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Baleen whales that are more likely to flee from predators, such as the sei whale, sing at lower frequencies to avoid detection. Credit: NOAA
Have you ever heard of “mosquito ringtones”? They’re phone ringtones that teens can easily hear but the frequency is too high for adults to hear, since humans naturally start losing the ability to hear higher frequencies in their 20s. New research suggests that some whale species use a similar trick—for very different reasons. Instead of trying to hide the sound of a ringing phone from adults, some whales call at frequencies too low for predators to hear.
Baleen whales are those that eat by filtering plankton through their mouths. Most baleen whale species are more solitary than toothed whales, such as sperm whales, orcas, or dolphins. That solitary nature is a vulnerability when hunted by orcas, the only natural predators of baleen whales. If orcas could listen for the songs of baleen whales, they would find them more easily when hunting. But the kinds of baleen whales most likely to flee from orcas communicate with sounds below 100 hertz, the lowest frequency orcas can hear. Blue whales, fin whales, sei whales, Bryde’s whales, and minke whales sing in a very low register, and orcas cannot hear their calls when they are more than a kilometer away.
Meanwhile, right whales, bowhead whales, gray whales, and humpback whales sing at higher frequencies, which orcas can hear. These also happen to be the species of whales more likely to fight back instead of trying to escape orcas. Scientists recently compared call and hearing frequencies across all baleen whale species and discovered these patterns. Researchers cannot know for certain why different species evolved to sing at different frequencies, but putting together all the evidence they have collected, there is a high likelihood that the fight-or-flight choice of different baleen species plays a role in the pitch of their voice.
