Imagine walking through your house with every light switched off. You know where the furniture is, but try finding your way around an unfamiliar room without touching anything and things get difficult very quickly. Now imagine doing it while flying through the dark at high speed, and catching insects on the way. That is what echolocation makes possible, and it is not just bats and dolphins that use it. A few birds, some shrews and other small animals use forms of it too, and, remarkably, humans can learn to navigate with tongue clicks and echoes. So what exactly is echolocation, and how does it work?
What is echolocation?
Echolocation is a way of sensing the world by making sounds and analysing the echoes that come back. The basic idea is surprisingly simple. An animal makes a sound, the sound travels until some of it hits an object and bounces back, and the animal’s hearing processes the returning echo. From the timing, direction, pitch and loudness of that echo, it can work out how far away an object is, which direction it is in, whether it is moving, how big it is, and whether it might be food or an obstacle in the flight path.
The most sophisticated echolocators do far more than detect that something is nearby. They continually adjust their calls and interpret a rapidly changing stream of echoes as they move. That is why scientists often call it biosonar, particularly for bats and toothed whales, and describe it as an active sense, as Wikipedia’s overview of animal echolocation explains: the animal is not just listening, but sending out the signal it listens for.
How does echolocation work?
The single most important piece of information is time. Sound travels at a known speed through air or water, so an echo that comes back quickly means a close object, and one that takes longer means something further away. But an echolocating animal is not simply waiting for one echo and calculating a distance. It compares the echoes reaching each ear, and many species also track changes in pitch and loudness. Because the animal is usually moving while it calls, each new echo also reveals how a target is moving.
This gets especially powerful when calls come in rapid succession. A hunting bat changes the timing and character of its calls as it closes in on an insect, and toothed whales adjust their clicks in the same way as they investigate and chase prey underwater.
Why are high frequencies so useful?
Many echolocating bats and toothed whales use ultrasound, sounds pitched above the upper limit of human hearing. Higher frequencies have shorter wavelengths, which means they bounce back more clearly from small objects such as a moth. The trade-off is that high-pitched sounds fade over shorter distances than low ones. So echolocation is not simply a case of calling as high as possible; each animal’s sonar has evolved to suit its surroundings and the things it needs to find.
How do bats use echolocation?
Bats are the animals most people link with echolocation, and with good reason. There are more than 1,400 bat species worldwide, according to Cairns Regional Council’s flying-fox guide, and most of them echolocate. Australia has around 90 species, and Perth Zoo notes that more than 60 of them are microbats, small insect-eaters that use echolocation to navigate and hunt in the dark. The Sydney Bat Network has recorded 19 species in the Sydney region alone, ranging in size across Australia from the ghost bat, at up to 150 grams, to tiny forest bats of about 3 grams.
Most of their calls are far too high for us to hear, but not all. Museums Victoria notes that the White-striped Freetail Bat is one of only two Australian bats whose echolocation is audible to people, and Perth Zoo describes its call as a distinctive “ting, ting, ting” at night. Different species also hunt in different ways. Some chase insects in open air, others weave through cluttered forest, and the ghost bat combines echolocation with sharp eyesight and hearing to snatch prey from the ground. As a bat closes in on an insect, it calls faster and faster, producing a rapid stream of echoes that sharpens its picture of the target, which is a long way from the popular image of an animal simply shouting into the dark.
Do flying-foxes use echolocation?
No. Australia’s flying-foxes are a different group. The Australian Museum notes that Grey-headed Flying-foxes do not echolocate, relying instead on well-developed sight and smell to find fruit, nectar and pollen. So when you see big flying-foxes heading out across the Brisbane or Sydney sky at dusk, they are navigating by eye, not by sonar. Worldwide, the picture is not quite that simple: a few fruit bats overseas, the rousette bats, have been shown to echolocate using tongue clicks, according to the same review of bird echolocation discussed below.
How do dolphins and whales use echolocation?
Echolocation also evolved in toothed whales, the group that includes dolphins, porpoises, orcas and sperm whales. Their problem is different from a bat’s: sound travels through water, where light fades quickly with depth and murky water can make eyesight almost useless. A dolphin produces short, powerful clicks inside its head, below the blowhole, and the melon, the rounded fatty structure on its forehead, focuses them into a forward beam. Returning echoes are picked up largely through the lower jaw and passed to the inner ear, as Wikipedia’s overview explains, giving dolphins sonar sensitive enough to tell different objects apart while hunting. Orcas use it too; despite the name “killer whale”, they are the largest members of the dolphin family, as I explain in my post on why killer whales are actually dolphins.
Do all whales echolocate?
No, only the toothed whales do. Baleen whales, such as humpbacks and blue whales, produce a huge variety of sounds, including the famous humpback songs, but they are not known to use the highly developed echolocation of their toothed relatives. So “whales use echolocation” is only true if you specify toothed whales.
What other animals use echolocation?
Bats and toothed whales have the most sophisticated and best-studied sonar, but they are not the only animals that use echoes. Here are the main echolocators, from the experts to the amateurs.
| Animal | Where it lives | How it uses echolocation |
|---|---|---|
| Microbats | Worldwide, including more than 60 Australian species | Mostly ultrasonic calls to navigate and hunt insects in the dark |
| Dolphins, porpoises, orcas and other toothed whales | Oceans and some rivers | Clicks focused by the melon to hunt and navigate underwater |
| Rousette fruit bats | Africa and Asia | Tongue clicks, unlike most fruit bats |
| Swiftlets | Caves across the Indo-Pacific, including tropical Queensland | Audible clicks to find their way through pitch-dark caves |
| Oilbirds | Caves in northern South America | Audible clicks to navigate caves, alongside sight and smell |
| Shrews | Leaf litter and burrows in many countries | Soft, high-pitched calls to explore their surroundings |
| Tenrecs | Madagascar | Tongue clicks to investigate their surroundings |
Oilbirds and swiftlets
The two birds on that list are the most surprising. Oilbirds live in caves in northern South America and click to find their way in the dark, while a number of swiftlets across the Indo-Pacific do the same. A review in Frontiers in Physiology found that echolocation occurs in at least 16 living bird species and has evolved several times among birds. Their clicks are pitched low enough for people to hear, which means a cruder system than bat sonar, and the researchers note that many questions remain, including whether some species use it outside their cave roosts at all. Oilbirds, for example, appear to rely mainly on vision whenever they can.
We have one of these birds right here in Queensland. Birds Queensland describes the Australian Swiftlet, a common sight in the tropical north, which breeds in caves and gorges and makes double clicks to navigate inside them, entering at reported speeds of up to 111 km/h. Standing at a cave entrance, you can actually hear them clicking in the dark.
Shrews and tenrecs
Some shrews, and the tenrecs of Madagascar, also make sounds that help them sense their immediate surroundings. Shrew echolocation was first described in the 1960s, the same review notes, and Wikipedia’s overview describes their calls as a short-range system for exploring their habitat rather than hunting. These animals are a useful reminder that echolocation is a spectrum, not an ability an animal either has or does not.
What about the aye-aye?
The aye-aye, a lemur from Madagascar, often appears on lists of echolocating animals, but that is misleading. It uses a remarkable technique called percussive foraging: it taps on wood with its extraordinarily long middle finger and listens to the result to detect hollow tunnels where insect larvae are hiding. That is an impressive form of listening, but it is not echolocation in the way a bat or dolphin does it, because the aye-aye is not sending out a call and analysing the echo that comes back from its surroundings. So it stays off the table above.
Can humans echolocate?
Yes, although our version is nowhere near as specialised as a bat’s or a dolphin’s. Some blind people have taught themselves to navigate by making sharp tongue clicks and listening carefully to the echoes, which tell them where nearby objects are and roughly what they are like. And you do not have to be blind to learn it. A 2021 study led by psychologist Lore Thaler at Durham University, published in PLOS ONE, trained 12 blind and 14 sighted adults aged 21 to 79 in click-based echolocation over 20 sessions spread across 10 weeks. Both groups improved substantially at navigating and recognising objects by echo, regardless of age or eyesight.
Three months later, Durham University reported that all of the blind participants said their mobility had improved, and 83% reported better independence and wellbeing. Those results are encouraging, but it is worth keeping them in proportion: they came from a small group and were based on what participants reported, not a large clinical trial. A later study from the same team, described in Scientific American, found that the training changed how the brain responds to echoes in both blind and sighted people. We may be visual animals, but our brains can get far more out of reflected sound than most of us realise.
Why did echolocation evolve more than once?
One of the most fascinating things about echolocation is that bats and toothed whales are not closely related, yet both evolved sophisticated sonar, an example of what biologists call convergent evolution. Each faced a version of the same problem. Bats fly at night, when eyesight is limited, and toothed whales hunt underwater, where visibility drops quickly with depth, darkness and murky water. Sound offered another way to gather information. But evolution did not produce identical systems. Bat and whale sonar work in different physical environments, use completely different anatomy, and have evolved different signals to suit their conditions. The birds, as the Frontiers review notes, arrived at their own version several times over. It is a bit like the octopus’s unusual circulation, which I wrote about in why octopuses have three hearts: a strange-looking design that makes perfect sense once you understand the problem it solves.
It is tempting to sum all this up as “seeing with sound”, and that is a fair starting point, but it undersells what these animals do. A bat is not receiving a photograph of its surroundings, and a dolphin is not hearing a perfect underwater picture. Their brains are processing a constant stream of sound and pulling out distance, direction, movement, shape and texture on the fly. So next time you are outside at dusk and see a small shape flickering around a streetlight, there is a good chance you are watching a microbat build a picture of the world from echoes, one call at a time.
Further reading
- Wikipedia: Animal echolocation
- Perth Zoo: Microbats in the garden (PDF)
- Sydney Bat Network: Echolocating bats (microbats)
- Museums Victoria: Bats, the flying mammals in dire need of a PR manager
- Australian Museum: Grey-headed Flying-fox
- Brinkløv, Fenton and Ratcliffe: Echolocation in oilbirds and swiftlets, Frontiers in Physiology (2013)
- Birds Queensland: Australian Swiftlet
- Norman et al: Human click-based echolocation, PLOS ONE (2021)
- Medical Xpress: Can echolocation help those with vision loss?
- Scientific American: Anyone can learn echolocation in just 10 weeks, and it remodels your brain