How echolocation lets bats, dolphins, and even people navigate by sound
The word "echolocation' says it all. But different animals have put their own twist on the sensory superpower.
In an environment without light, or where sight is otherwise useless, some creatures have learned to thrive by sound. They rely on calls, clicks, and twitters to create a kind of map of their surroundings or pinpoint prey. That ability is called echolocation, and a simple way to understand how it works is to crack open the word itself.
What is echolocation?
Imagine an echo that locates things. The sound hits an object and bounces back, relaying information about a target’s whereabouts or cues for navigation. When Harvard University zoologist Donald Griffin coined the word “echolocation” in the journal Science in 1944, he was describing how bats rely on sounds to “fly through the total darkness of caves without striking the walls or the jutting stalactites.”
In the decades since, scientists have identified many other animals that use echolocation, aka biosonar. For example, at least 16 species of birds echolocate, including swiftlets and nocturnal oilbirds, which roost deep in South America’s caves. Laura Kloepper, an expert in animal acoustics at the University of New Hampshire, calls this shared ability an example of convergent evolution, in which “you have two unrelated species evolve the same adaptive strategy.”
How does echolocation work?
To find fish in deep waters, or avoid crashing in the inky night, whales and bats produce loud ultrasonic sounds at frequencies all the way up to 200 kilohertz. That is way beyond human hearing (most adults can’t perceive pitches above 17 kilohertz).
[Related on PopSci+: 5 sounds not meant for the human ear]
Why do specialized echolocators use ultrasonic sound? “High-frequency sounds give really fine spatial resolution,” Kloepper explains. Hertz is a measure of the distance between each acoustic wave: The higher the hertz, the tighter the wave, and the smaller the detail captured by the vibration of energy in the air. If you were to echolocate in a room, a big, low-frequency wave might simply reflect off a wall, Kloepper says, while an echo from a higher-frequency sound could tell you where the doorway or even the knob was.
Echoes, if you know how to interpret them, are rich in information. As Kloepper explains it, when an animal with the ability hears a reflection, it examines that sound against an “internalized template” of the call it sent out. That comparison of echo versus signal can yield the distance to a target, the direction it might be traveling in, and even its material make-up.
Ultrasonic calls give another bats boost, too—they rely on next-level frequencies to find mates. Many species of moths hunted by bats have evolved ears attuned to these frequencies as a means of survival.
What animals use echolocation?
Of the echolocating critters, bats and toothed whales like dolphins are the all-stars. Dolphins are able to detect objects more than 300 feet away, and can even tell if a target has fluid inside of it. Bats’ range maxes out at about a dozen feet, but they can sense objects while flitting through a dense forest or a huge bat swarm. Using sound, both types of mammals are able to discern differences in location down to fractions of an inch. Other animals have their own versions of sonar, too, adapted to their unique features and needs.
Bats
Fossils indicate that bats have been guided by sound for at least 52 million years, which is longer than humans have even existed. Today, hundreds of species in this mammalian group can echolocate, which they use to chase down mosquitoes, moths, and other prey. Some insectivorous bats are so adept at this skill, they can spot motionless bugs hiding on leaves in the dark of night. In response, many insects have evolved defenses against bat sonar—a struggle that biologists have likened to an arms race. Luna moths sprout long tails that might act as reflective decoys, confusing bats. Other flutterers emit ultrasonic signals of their own to jam the enemy’s sonar.
[Related: How fast is supersonic flight?]
To make ultrasound, a bat vibrates a specialized organ in its throat called a larynx. It’s not too different from how the human voice box works, except the bat produces a much higher frequency sound. Certain bat species then release the sound from their mouths, while others screech from the snout, using an elaborate nasal structure nicknamed a nose-leaf.
Whales
Dolphins, orcas, and other toothed whales echolocate for the same reasons as bats do: to chase down tasty prey and navigate through darkness. But these aquatic mammals emit ultrasound in a completely different way. Inside whale heads, often close to their blowholes, sit lip-like flaps. When the animals push air across the flaps, the appendages vibrate, producing clicks. “It’s just like if you inflate a balloon and let all the air out of that balloon. It makes a pbbft noise,” Kloepper says.
The curves of dolphin skulls propel that noise into fatty structures at the front of their heads, called melons. These, in turn, efficiently transmit vibrations in seawater. The waves bounce off prey or other objects, but the whales don’t rely on external ears to hear the echo (their ear canals are plugged up with wax). Instead, the vibrations are channeled via their jawbones, where sound is received by fat-filled cavities so thin that light can pass through them. The cavities are near the whales’ inner ears, which sense the echoing clicks. The process can reveal all sorts of details: where a fish is, where it’s going, and how fast it’s swimming.
Shrews
Shrews have sensitive whiskers but poor eyesight. To supplement their senses as they explore their forest and grassy meadow habitats, they might use a coarse form of echolocation, which Sophie von Merten, a mammalogist at the University of Lisbon in Portugal, calls “echo-orientation” or “echo-navigation.” This ability could “give them a hint that there is an obstacle coming,” she says, such as a fallen branch detected by the shrews’ twitters. Their bird-like sounds are faint, but audible to humans.
The extent of shrew echo-navigation isn’t entirely clear. In a 2020 “experiment, von Merten and a colleague found that, when shrews are introduced to new environments, the wee mammals twitter more frequently. Von Merten says it’s likely they are sensing the unfamiliar location by these vocalizations, but another interpretation could be that the captive animals are stressed. That’s a hypothesis she doesn’t find very convincing, though her ongoing research will measure shrew stress, too.
Soft-furred tree mice
In 2021, a study in the journal Science found that four species of soft-furred tree mice echolocate via squeaks. The rodents, which belong to the genus Typhlomys, meaning “blind mouse,” live in dense bamboo forests in China and Vietnam. Examining the animals’ behavior, anatomy, and genetics, the researchers concluded there was “strong evidence” that these tree mice are a newly discovered “echolocating lineage within mammals.”
Could there be other undiscovered creatures out there that echolocate? “I think it’s very likely,” Kloepper says. She adds that it’s hard to tell which animals beyond mammals and birds display the behavior, given “just how little we know about vocalizations of many cryptic species.”
Humans
Unlike bats, people aren’t born with the innate power of echolocation—but we can still make it work. In his original 1944 paper, Griffin discussed a, such as captains listening for echoes of ship horns against cliff faces, or those who are blind following the taps of their canes.
[Related: Bat-like echolocation could help these robots find lost people]
Perhaps the most famous human echolocator is Daniel Kish, the president of World Access for the Blind, who described how he navigates by clicking his tongue in a 2020 Popular Science interview. “The longer the time delay between the noise emitted and the return,” Kish said, “the farther away an object is.” Kish has taught others to click like he does. Similar examples show that echolocation in humans doesn’t require special brains or unnaturally good hearing—it’s a learned behavior that can be picked up in about 10 weeks of practice and training.