Biosonar

Home to Roost Most bat species will roost in the same location every night, joining a large colony of bats that cluster together for warmth and security. Bats have been known to demonstrate remarkable acts of altruism to support the colony. In some cases, when a bat is ill and cannot hunt for its own food, other bats from the colony will bring food back to it.

Small, quick-moving insects are the main prey for many bats. As if tracking a fast, fluttery food source isn't tricky enough, the task of hunting is made even more difficult because most bats are only active at night, dusk and dawn. One reason for avoiding daytime is to avoid the fierce flying predators such as falcons, hawks and owls that are active in daylight. Bats also take advantage of the abundance of insect species that are active at night. To help them find their prey in the dark, most bat species have developed a remarkable navigation system called echolocation, which is also called biosonar.

To understand how echolocation works, imagine that you're standing in an "echo canyon." You stand on the edge of the canyon and shout "hello." An instant later, you hear your own voice coming back to you. The way this works is pretty simple. When you shout, you produce sound by rushing air from your lungs past your vibrating vocal chords. These vibrations cause fluctuations in the rushing air, which form a sound wave that travels across the canyon. The rock face on the opposite side of the canyon deflects the air-pressure energy of the sound wave. The wave then moves in the opposite direction, heading back to you. In an area where atmospheric air pressure and air composition is constant, sound waves always move at the same speed. If you knew the speed of sound in the area, and you had a very precise stopwatch, you could use sound to determine the distance across the canyon. This is the basic principle of echolocation. Bats make sounds the same way we do, by moving air past their vibrating vocal chords. Some bats emit the sounds from their mouth, which they hold open as they fly. Others emit sound through their nose.

Bats use echolocation to catch prey.

In the case of most bats, the echolocation sound has an extremely high pitch. It's so high that it's beyond our hearing range. But the sound behaves the same way as the sound of your shout in the echo canyon. It travels through the air as a wave, and the energy of this wave bounces off any object it comes across. A bat emits a sound wave and listens carefully to the echoes that return to it. The bat's brain processes the returning information. By determining how long it takes a noise to return, the bat's brain figures out how far away an object is. But the information doesn't stop there.

Bat Life Bats are extremely susceptible to extinction because of their reproductive habits. Most bat species give birth to only one baby per year, so they multiply at a relatively slow pace. Since bats have a fairly long life span (as long as 30 years in some species), the loss of one female bat has a major effect on the rate of reproduction.

Incredibly, the bat can also determine where the object is, how big it is and in what direction it is moving. The bat can tell if an insect is to the right or left by comparing when the sound reaches its right ear to when the sound reaches its left ear: If the sound of the echo reaches the right ear before it reaches the left ear, the insect is obviously to the right. The bat's ears have a complex collection of folds that help it determine an insect's vertical position. Echoes coming from below will hit the folds of the outer ear at a different point than sounds coming from above, and so will sound different when they reach the bat's inner ear.

A bat can tell how big an insect is based on the intensity of the echo. A smaller object will reflect less of the sound wave, and so will produce a less intense echo. The bat can sense in which direction the insect is moving based on the pitch of the echo. If the insect is moving away from the bat, the returning echo will have a lower pitch than the original sound, while the echo from an insect moving toward the bat will have a higher pitch.

A bat processes all of this information unconsciously, the same way we process the visual and aural information we gather with our eyes and ears. And speaking of eyes -- bats also process visual information. Yeah, we've all heard the phrase "blind as a bat" – but don't believe it. Contrary to popular belief, most bats have fairly acute vision. They use echolocation in conjunction with vision, not instead of it.

The Other Bat Signal One of Batman's most innovative gadgets is the sonic device he carries in his boot heel. It can summon swarms of bats instantly to create mass chaos at any scene so that Batman can create incredible diversions or make dramatic escapes. OK – so the big question here is, "Could this be real?" The short answer is, in theory, yes this might work. Several species of bat use sound to communicate (but they also use sight and smell). For example, consider pallid bats, which commune in social groups from as little as a dozen up to 100 bats. Pallids are known to use a particular "directive" call to rally the group toward a new roost. Pallid moms also use a special call to find their babies. Another example can be seen in response to distress cries. Research has shown that some bats will respond to distress cries from bats of their own species, but not of other species. So, if Batman's sonic alarm were set just right so that it resembled a particular distress cry or directive call, and he was within range of the bat species his alarm is mimicking, it just might work. It's also worth mentioning that the opposite could happen, too. A nemesis of Batman could possibly use sound to keep the bat swarm at bay. Some research suggests that super high-frequency sound can be used to repel bats.