BAT SENSES AND ECHOLOCATION | Facts and Details

BAT SENSES

bat echolocation

All bats have eyes and can see. Many kinds of bats don’t see very well and rely on echolocation (See Below). Some have extraordinary night vision. Fruit species in particular have very sensitive eyes, which they use for navigating instead of echolocation. Even though they see well at night they need a little light and thus can not see in the complete darkness of caves, which is one reason why they roost in trees rather caves. .

Many bats have huge ears. Some are reminiscent of those belong to gremlins in the movie “Gremlins” The ears of some species are so large they coil up like a party favors when they sleep so they don’t disturb their roosting neighbors.

Bats can sense it is dark and time to leave a cave even though they can not see it get dark and can not sense the cooling temperatures of approaching night because the temperatures in the cave are relatively stable throughout the day.

Bats also have an excellent sense of smell. They can sometimes detect food sources a mile or more away. The male hammerhead bat has a snout so big in relation to the rest of its body it looks like a mouse-size hippopotamus with wings.

Bat Echolocation

Most bats navigate their way through forests and open spaces, and locate prey and avoid predators, using echolocation — a biological sense based on the same principal as radar. Bats send out signals that bounce back and are detected and analyzed, giving bats a detailed picture of objects struck by the signals and their distance from the bat.

In bat echolocation ultra-high frequency pulses emitted 10 times a second sounds are emitted from the bats mouth (sometimes through a labyrinth of lips that direct of the sound in different direction) and are detected with the bat’s ears of with ear-like organs comprised of folds and flaps that are located on the face of the bat and act like radar dishes.

Bats decode information that bounces back. The time delay and angle provides information about distance, location, movement, the composition of an objects, and possibly even altitude measurements, allowing the bats to zero in on the targets and avoid obstacles or threats.

Echolocation is used primarily by small insect-eating bats, whose eyes have become so small they are of little use. Leaf-nosed bats have a leaf-shaped nose, which is used for vocalization rather than their mouths. It both modulates and focuses the sound. Echos are picked up with the ears.

Bat Sounds

A flying bat using echolocation uses sound between 50,000 and 200,000 vibrations a second. Most human-heard sound are several hundred vibration per second with some people, mostly children, able to hear sounds with 20,000 vibrations a second. Very high sounds are also the basis of sonar used by submarines and ships to detect objects in water. The effect is similar to radar but radar uses radio waves whereas sonar and bat echolocation use sound waves.

David Attenborough wrote: “It is reasonable to guess that the shrew-like ancestors of these bats used high-pitched sounds to find their way in the dark, just as living shrews do today. It is no surprise therefore that their descendants still do the same. What is surprising — indeed astonishing — is the way in which bats have elaborated those simple ultrasonic squeaks into the superb navigational and hunting system they use today.”

ultrasound signals emitted by a bat, and the echo from a nearby object

Bats generate sound with the larynx in their throat and direct it through both their nose and mouth and pick up sound with their highly sensitive ears that it many cases can be twisted to detect sound and are translucent, ribbed with cartilage and laced with blood vessels. Bats swing their head rapidly from side to side, sending out sound and picking up echos, and deducing information from those echos, as they fly at speeds of up to 40 mph.

Bats send out sound in short bursts, 20 to 30 times a second. Most bats wait to receive the echo of one signal before emitting the next. The closer the bat is to an object the shorter the time taken for the echo to come back, so they can increase their accuracy as its closes in for the kill. When it eating it so momentarily blind as it can not send out sound in a normal way with food in its mouth. Some species avoid this problem by squeaking through their noses and have developed unique megaphone-like structures to achieve this end.

Attenborough wrote: “Many bats focus the sound beam using a structure called a nose lead that surrounds the nostrils. This varies widely in shape from species to species. There are bowls, slits, leaves, vertical spears, horseshoe-shaped cups and shapes that are so complex and convoluted that they can not be compared with any simple object. Many are mobile in that their owners can vary the width and character of the beam they project. The sound themselves are emitted as a series of extremely short stabs, They are so high-pitched they are far beyond the range of our own ears. But they are extremely powerful. If we were able to transport them down at their true voice they would sound as loud to us as a jet engine.”

Bat Echolocation Vibrations

The bat echolocation system is so sensitive that bats can detect the footsteps of insects, the scales on moths, the difference between a rock and a beetle, the difference between flowers and other plants and make out a wire as thin as a human hair suspended across its flight path. Many bats can fly fine if they are blindfolded but start crashing and bumping into objects if their ears are plugged and their echolocation system is messed up.

People can hear squeaks and other sounds made by bats but these are their social vocalizations. Like a dog whistle, their echolocation are too high for people to hear. If they were in the human hearing range they would be as loud as a jackhammer, a 747 taking off or a Heavy Metal band playing with the volume on their amplifiers turned up to 11. Echolocation of 145 decibels have been recorded. The sounds are so loud in fact that bat ears have a muscle that temporarily disconnects their ear drum when the clicks are too loud.

“The intensity and frequency of these sonar probes varies according to the bat’s needs,” Attenborough wrote. “Those for general navigation are not as intense as those which the bat makes when homing in on a particular target. All such sounds are reflected back from surrounding objects and received by the bats’s large ears which also vary in shape from species to species. These echoes, are, of course, very faint, as a bat’s sense of hearing has to be extremely sensitive. If the bat hears it shrieks with its own hyper-sensitive ears, it would deafen itself, but it is able to switch off its sense of hearing every time it emits a stab of sound. And it has to do that as frequently as two hundred times a second.”

Sometimes people can feel echolocation from bats if they get close enough. The range of detection for bats is generally a few feet to several yards. The higher the pitch the smaller the surface of the echo. The louder the clicks the more distant an object is. The more frequent the clicks the more up to date the information the bat receives,. Some bats can emit clicks at a rate of two hundred a second and decipher each click.

Experiment That Shows How Bats Turn Echolocation Signals into a 3-D Image of Moving Prey

Melville Wohlgemuth, a neuroscientist at Johns Hopkins University, studies bats. Rachel E. Gross wrote in Smithsonian magazine: When Wohlgemuth noticed that the bats in his lab were doing something weird, he knew it had to have a purpose. Specifically, his bats were cocking their heads and waggling their ears. To find out what they were doing, he designed an experiment as intricate as a bat’s sound system — one that required amenable bats, video game cameras and some rather unlucky mealworms. [Source: Rachel E. Gross, Smithsonian magazine, November 2016]

“First, the experiment had to take place in total darkness to ensure that the bats relied only on echolocation. (Contrary to popular belief, bats are not blind — they just tend to have poorer vision.) Wohlgemuth and colleagues used infrared motion-capture cameras — the same kind gamers use — to film each subtle movement without adding pesky visible light. Meanwhile, ultrasonic microphones recorded their high-pitched chirps.

“Next, he had to get the darned things to sit still. After collecting dozens of big brown bats from a series of filthy Bethesda attics, he began training them to sit patiently on a platform while dinner came to them. Not all bats complied, but after two weeks, many became “really chill” around him. It helped that he rewarded their efforts with a juicy grub, Pavlovian-style. “I’m much better at training bats than I am at training dogs,” he says.

“Finally, Wohlgemuth developed a fishing line-and-pulley system to deliver mealworms to his bats. When he ran the experiment, he found that the more abruptly the insects moved, the more the bats cocked and waggled their ears in an effort to localize their prey. “When the target got closer, the ears moved apart, and when the target was further away, the ears moved closer together,” says Cindy Moss, a neuroscientist who runs Wohlgemuth’s lab and co-authored the paper.

“Cats, dogs and even humans pivot their ears to orient themselves toward sound. But this was a bit more sophisticated. By rapidly waggling their ears just after they chirped, bats tracked the tiny change in frequency — think the sound of a car speeding past — as the mealworms moved in one direction or the other. With each movement, the bat took another “snapshot” of the sound, stringing them together to create the acoustic version of a panoramic photo. “The movement of the ear is like getting different perspectives on the same sound,” says Wohlgemuth, who reported his findings with Moss in the journal PLOS Biology in September 2016.

Echolocation of Nectar-Feeding Bats

Some tropical flowers reflect sound so nectar-seeking bats can find them more easily. Susan McGrath wrote in National Geographic: “Glossophaga commissarisi, a tiny, winged mammal with a body no bigger than your thumb, flits among the flowers of Mucuna holtonii, lapping nectar, much as hummingbirds and bumblebees do. In exchange it pollinates the plant. In daylight flowers can flaunt their wares with bright colors such as scarlet and fuchsia, but at night, when even the brightest hues pale to a moonlit silver, Mucuna flowers resort to sound to catch the ear of nectar bats. [Source: Susan McGrath. National Geographic, March 2014]

“Bats use high-frequency sound as a tool. With their vocal cords, they bang out short, swift bursts through their nostrils or mouths, molding airwaves and interpreting the pattern changes that ricochet back to their sensitive ears. The incoming information is processed fast and continually, allowing bats to adjust their course in mid-flight as they streak through the air after a mosquito or race among flowering trees.

“Most bats feed on insects, and they often use powerful, long-range calls, pumped out with every upstroke of their wings. Nectar bats send gentle but very sophisticated calls, which scientists refer to as frequency modulated. These calls trade distance for detail. Most effective within 12 feet, they reflect back pictures that convey precise information about a target’s size, shape, position, texture, angle, depth, and other qualities only a nectar bat can interpret.

“In the darkened Mucuna ballroom at La Selva Biological Station in northern Costa Rica Selva a beacon petal’s cupped shape acts as a mirror, fielding bat calls and bouncing information back hard and clear. With eyes and ears and nose leaf trained straight on the beacon, a bat snaps onto the blossom in a high-speed embrace. The fit is exact. The bat crams its head into the cupped opening, hooks thumbs onto the beacon’s base, tucks its tail, whips its hind feet up. Braced high on the pea pod, it thrusts its snout into the garlicky opening. The bat’s long tongue springs a hidden switch, exploding the pea-pod keel. As it laps deep in the flower’s nectary, spring-loaded anthers burst from the keel and gild the bat’s tiny rump with a spray of golden pollen.

“Bang! Bang! Bang! Bang! Ten blossoms detonated and licked dry, and the bats are gone. Their high-octane metabolism and meager sugar-water diet don’t allow for lingering. Each bat makes several hundred flower visits every night. Mucuna holtonii, with their exploding mechanism and generous snort of nectar, are among the rare flowers that warrant actual landings. (Nectar bats can empty the flowers of less lavish species in a hover lasting a mere fifth of a second.)

“The 40 or so species of the subfamily Glossophaginae are the aerial elite of nectar-drinking bats. They belong to the family of New World leaf-nosed bats, native to the tropics and subtropics of the Western Hemisphere. Their fleshy nose embellishments—the eponymous nose leaves—fine-tune the bats’ virtuoso echolocation calls.

“Nectar bats evolved in fruitful partnership with specific families of flowering plants, a relationship biologists call chiropterophily—from Chiroptera, the mammalian order of bats, and phily, from philia, Greek for “love.” But this is no love story. The driving force behind the bat-flower partnership is not romance but the primary business of life: survival and reproduction. Trading nectar for pollination is a delicate transaction, one that presents plants with a quandary. It behooves night-flowering plants to be thrifty with their nectar, because well-fed bats will visit fewer flowers. But if a plant is too stingy, a bat will take its services elsewhere. Over millennia, bat-pollinated plants have evolved a neat solution: They sidestep the problem of nectar quantity (as well as quality) by investing instead in maximizing the bats’ foraging efficiency.

Feeding Bats Able to Jam Sonar of Rivals

Mexican free-tailed bats are able to sabotage the sonar systems of rival bats trying to capture a meal. Michelle Nijhuis wrote in Smithsonian magazine: Aaron Corcoran, a biologist currently at Wake Forest University, was studying the hunting habits of Mexican free-tailed bats in Arizona and New Mexico when his ultrasonic microphones picked up an unfamiliar sound. Bats use a variety of calls — most of them are inaudible to humans — for both navigation and communication, but the free-tailed bats sent this particular signal only when nearby bats were about to snag their prey. [Source: Michelle Nijhuis, Smithsonian magazine, April 2015]

“So Corcoran and colleague William Conner, who studies animal communication, tethered live moths to a streetlight with lengths of fishing line and waited. When approaching bats emitted their characteristic “feeding buzz” — a rapid series of echolocation calls that bounce off a prey item and back to the bat — the researchers played recordings of the newly discovered call through loudspeakers. It dramatically reduced the bats’ chances of capturing the moths, shrinking their hunting success rate from about 65 percent to 18 percent. The call, which spans multiple frequencies, overlaps with the feeding buzz, creating a blur of noise that “jams” the echolocation signal, much as military forces jam enemy radio communications.

“To be sure, other bat species also have specialized vocalizations for keeping competitors away from food. A common bat in North America, known as the big brown bat, makes a series of chirps that appear to claim dibs on flying insect prey, and pipistrelles in Europe emit complex sounds to warn other bats away from a patch of rooftop or urban park, along with the food resources within.

“But Mexican free-tails, which live in enormous colonies that can exceed a million individuals, are the only echolocating animal known to actually jam signals. Corcoran, who describes bats as “incredibly adorable,” speculates that the adaptation evolved in response to the intense competition among members in the same crowded colony. “At some density,” Corcoran says, “your friends become your enemies.”

Blind Man Who Uses Echolocation to Ride a Bike

National Geographic reported: What Daniel Kish does, astonishingly, elegantly, makes you wonder how much untapped potential lies within the human body. Kish was born with retinal cancer, and to save his life, both eyes were removed by the time he was 13 months old. He soon started making a clicking noise with his tongue. It seemed to help him get around. Now 47, he navigates primarily using echolocation. Yes, like a bat. He’s so good, he can ride a bicycle in traffic. His group, World Access for the Blind, teaches others the art of the click. [Source: National Geographic, June 2013]

Kish told National Geographic: “Sound waves are produced by every tongue click. These waves bounce off surfaces all around and return to my ears as faint echoes. My brain processes the echoes into dynamic images. It’s like having a conversation with the environment. Each click is like a dim camera flash. I construct a three-dimensional image of my surroundings for hundreds of feet in every direction. Up close, I can detect a pole an inch thick. At 15 feet, I recognize cars and bushes. Houses come into focus at 150 feet.

He still use a long white cane. “I have difficulty detecting small items at low level or places where the ground drops off.” When asked what is it like riding a bike using echolocation, he said “It’s thrilling but requires very focused and sustained concentration on the acoustics of the environment. I click as much as twice per second, way more than I usually do.

Image Sources: Wikimedia Commons

Text Sources: Mostly National Geographic articles. Also David Attenborough books, Live Science, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated November 2024