1. Bats are not blind: they use eyes and sound together
Bat Conservation International lists "bats are blind" as a myth. It says bats' eyes are far from blind and work together with their other senses[1]. The U.S. Geological Survey agrees: bats have small eyes with very sensitive vision, which helps them see in conditions people might consider pitch black[2].
Sight and sound are good at different jobs. In a study of two bat species, vision worked better for large objects such as trees, while echolocation worked better for small ones such as insects. For a mosquito-sized target, one species could detect it by echo from about 2 to 4 m (6.5 to 13 ft) away, but by sight only from about 0.5 to 1 m (1.6 to 3.3 ft)[3].
This article is about bats that use sound to find their way, especially insect hunters.
2. How a bat turns an echo into a distance
A bat makes a short call, often too high-pitched for people to hear. The call bounces off whatever is ahead, and the bat's ears catch the echo. The time between the call and its echo helps the bat estimate how far away the object is: a short delay means close, a longer delay means farther[4].
How precisely can a bat judge that wait? In lab tests with big brown bats, short sweeping calls like the ones used when closing in on prey allowed a distance accuracy of about 1.5 cm (0.6 in). Long, steady search calls were about ten times less precise, around 15 cm (6 in)[4]. Different calls are good at different tasks, which is one reason bats change them during a hunt.
3. How a bat's calls change from searching to catching
A hunting bat does not call at one steady pace. Researchers describe a progression: while searching, calls are fairly long and spaced out. As the bat closes in, it calls more often and each call gets shorter[5].
Numbers from one species, the big brown bat, show the pattern. In the approach phase it makes about 20 to 80 calls a second, each lasting 2 to 5 milliseconds, and each call sweeps steeply from about 65 kHz down to 25 kHz. In the final "terminal buzz" just before the catch, calls shrink to 0.5 to 1 millisecond and reach about 170 a second[4]. Other species can go higher: the Ratcliffe review reports buzzes of more than 100 calls a second, and in some species up to and beyond 200[5]. These values depend on species and situation; they are not fixed rules.
Why call faster when the insect is close?
A flying insect keeps changing direction, and the closer the bat gets, the more its position matters. Researchers describe the buzz as a way to update the position of a moving target quickly. More calls means more echoes, so the bat gets fresh information more often right when it needs it most[5]. That is the main explanation, and it is based on measurements and reasoning rather than on being able to ask the bat.
4. What limits how fast a bat can call: a muscle
Could a bat simply call even faster? A 2011 study in Science on Daubenton's bat found that the limit is not the echo, which comes back quickly enough. In that bat, the study reported, the limit is the "superfast" muscle that works the voice box, which can switch on and off far faster than ordinary muscles. News coverage of the study reports buzz calls of up to about 190 a second[6].
A simple way to picture it: even if the bat's brain "wanted" more calls, the body has to keep up. The speed is set by how the animal is built.
5. How people discovered that bats use echoes to find their way
In the late 1700s the Italian scientist Lazzaro Spallanzani found that blinded bats still flew and avoided obstacles well. Another researcher, Louis Jurine, found that bats with their ears plugged with wax crashed into things. Even so, scientists for a long time believed bats found their way by touch. The sounds themselves were out of reach: bat calls are above the range of human hearing[7].
In 1938, as a Harvard undergraduate, Donald Griffin took a cage of bats to the lab of a physicist, G. W. Pierce, who had equipment that could detect ultrasound. The bats were making intense sounds nobody could hear. Later, working with Robert Galambos, Griffin showed that those sounds were needed for normal flight: deafened bats, or bats that could not call, collided with obstacles. Griffin gave the ability its name, echolocation[7].
6. How some moths answer back with their own clicks
Moths are prey, but some have defenses. A 2019 study in Scientific Reports looked at ermine moths of the genus Yponomeuta. They are deaf, so they cannot hear a bat coming. But as they fly they make ultrasonic clicks with a small patch on each hindwing, twice with every wingbeat[8].
The authors argue that these clicks sound like the warning clicks of tiger moths, which can taste bad to predators, so the two groups act as "mimics" of each other's sound. They suggest the clicks warn bats that the moth is unpleasant to eat, and say this still needs testing with live bats[8]. It is a good reminder that the hunt is not one-sided: prey evolve too.
7. Try it: how fast can you clap?
Clap as fast as you comfortably can for five seconds while a friend or family member counts, with space around you, and stop if your hands hurt. Repeat three times and divide the average by five. Compare your claps per second with the bat's roughly 170 calls per second in a buzz. Each bat call is a tiny, precise movement of the voice box, repeated far faster than any hand can manage.
To read more, the sources below include free articles from Bat Conservation International and the U.S. Geological Survey. If you spot bats at dusk, watch from a distance and never try to touch one.