How do bats navigate? How do bats navigate? Can a bat send a signal with a frequency
You might think that there is nothing in common between a radar and a bat, between a device that 20th-century technology prides itself on and a small animal with big wings. However, it is not.
Bats are very peculiar animals. They are found mainly in the south. These are nocturnal inhabitants. They sleep during the day, and as soon as the sun goes down, they fly out of their hiding places. This way of life of winged animals made it difficult to observe them, and legends were formed about them.
Bats have acute hearing. It helps them hunt for insects by sound. They have very large ears and mouth.
Bats' ears are extremely mobile. Hearing the slightest noise, the mouse picks them up and listens, and when there is a loud noise, quickly bends them back.
It has long been noted that bats can fly in complete darkness without bumping into obstacles. One hundred and fifty years ago, one scientific naturalist decided to find out what helps them navigate in the darkness.
He covered the bat's eyes and let it into the dark room. The blinded mouse flew past obstacles, deftly avoiding them.
A hole was made in the partition. The mouse skilfully flew through it. The room was strung up and down with wire, hung with bells. Deprived of vision, the mouse flew around the room for hours and never touched the wire; the bells were silent.
We carried out the experiment with another mouse and the same thing happened again. Then we coated the mouse with varnish. Deprived of the sense of touch, she continued to fly around the room without bumping into the wire.
The mouse was deprived of each of its sense organs in turn. This did not affect the flight at all: she flew just as confidently.
Finally they plugged her ears. She took off, and immediately bells began to ring throughout the room. The mouse lost its orientation and rushed around, bumping into obstacles. It became clear that hearing, the finest hearing, allows the mouse to fly around obstacles that it encounters along the way.
But how is such precise orientation achieved? Where is the source of sound that helps the mouse in its skillful flight? No biologist could answer this. The mystery of bats remained unsolved for a long time.
In 1920, it was suggested whether mice made a special sound that was not audible to humans. At the time when the first experiments with bats were carried out, no one knew about this. At that time, they did not know about the existence of ultrasound, which is now well studied.
If the number of vibrations of air particles is more than 20 thousand per second, a person cannot hear such a high tone. This is ultrasound. What we hear is only a small part of the sounds that exist in nature.
In 1942, biologists tested bats again. But now they were already armed with the achievements of science of the 20th century. Biologists not only repeated all the old experiments, but also supplemented them by gagging the mice. It had the same effect on her as hearing loss.
The assumption about ultrasound began to be confirmed. But science requires absolutely clear, irrefutable evidence. If ultrasound cannot be heard, scientists decided to see it and, using special equipment, recorded it on tape. Traces of very high frequency vibrations were imprinted on it.
When they were counted, it turned out that the mouse produces an extremely high-pitched sound - from 25 thousand to 70 thousand sound vibrations per second.
After painstaking experiments, it turned out that the bat produces sound and itself perceives it after being reflected from obstacles.
A recording of the ultrasound emitted by a bat has revealed how the mouse uses its orientation apparatus. It turned out. that the mouse emits ultrasound intermittently.
Ultrasonic echo warns the bat of an obstacle in its path
After a very short “scream” she falls silent. Then “shouting” again and again falls silent. She makes about ten such cries per second before takeoff, about thirty in flight and about sixty when she flies close to an obstacle.
The next shout is made immediately after the reflected sound returns. The shorter the path to the obstacle, the faster the echo returns and the more often the mouse screams. Obviously, by the frequency of these cries, she senses the distance to the obstacle.
The bat uses sound waves in much the same way as radio waves are used in radar. This is a kind of locator using ultrasound.
Sound audible to humans is not suitable for this purpose. It does not have the same properties as ultrasound. Ultrasound waves are very short, making them extremely easy to send out in a narrow beam. In addition, they reflect well from minor obstacles and even reflect from wire and branches. And this is precisely necessary in order to detect the smallest obstacles, distinguish them from one another and determine the direction.
When a mouse is in flight, its mouth acts like a sound spotlight. It seems to “illuminate” the path with a narrow beam of sound. The huge ears of the mouse are directed in the same direction and catch the reflected ultrasound.
This type of sound reconnaissance works excellently. If the path is clear, the mouse flies straight, but if there is an obstacle in the way, the mouse will hear it and turn to the side. The maximum range at which the mouse senses an obstacle is about 25 meters.
But there are obstacles that she still cannot detect. Biologists often observed that a mouse, skillfully flying around all obstacles in the dark, came across a human head. This was completely puzzling, but now we can explain this strange behavior of the mouse.
Hair, absorbing ultrasound very strongly, does not reflect. And since there is no echo, the obstacle is not detected and the mouse can easily stumble upon a human head. However, this rarely happens in the life of bats; they successfully use natural sound locator in their night flights.
Dipper butterfly Bertholdia trigona- the only animal known in nature that can protect itself from bats by jamming their location signals. Mice cannot learn to catch this type of bear, which produces characteristic ultrasonic clicks. However, how exactly do butterfly clicks work? B. trigona on bats was unknown. American biologists conducted behavioral experiments in which they tested three possible mechanisms. It turned out that the signals emitted B. trigona, reduce the accuracy with which the bat determines distances to it. As a result of the clicks emitted by the butterfly, the bat changes the nature of its signals, which makes it even more difficult to catch the butterfly. The authors believe that this behavior B. trigona could have arisen from a more ancient method of defense, known among some butterflies, when acoustic signaling is accompanied by the release of chemicals that repel the predator.
Bats and moths have been competing in an evolutionary race for at least 50 million years. In the process of this struggle, butterflies have developed a fairly simple design of auditory organs, which helps to quickly warn of approaching danger and trigger the reaction of avoiding a predator. Butterflies from the bear family, or Arctiidae, are also capable of producing ultrasonic clicks, with different species doing so in different ways. Many of them make clicks quite rarely, but the acoustic signal is accompanied by the release of odorous substances that repel bats. Other species have learned to imitate these inedible butterflies by clicking and not emitting any scent (Barber and Conner, 2007). Another method of defense is clicking in order to frighten an inexperienced bat. This method, however, is not very reliable, since the mice learn and after a few attempts they stop paying attention to the clicking of the butterfly.
Recently, American scientists from Wake Forest University showed that one species of bear, Bertholdia trigona, can emit frequent ultrasonic signals that jam the echolocation signals of bats (Corcoran et al., 2009). It is remarkable that bats are not able to learn to deal with this obstacle: after numerous attempts, the mouse still fails to catch the butterfly. Now the same authors set out to find out the mechanism by which B. trigona so skillfully protects itself (Corcoran et al., 2011). They proposed three hypotheses.
According to the first - illusory echo hypothesis, - the bat may confuse the butterfly's signals with the echo of its own signal from an object that does not exist. In this case, the mouse must change its flight path, flying away from a non-existent object. According to the second - distance interference hypothesis, - signals emitted by the butterfly can reduce the accuracy of the bat's determination of the distance to the prey. This can occur if the butterfly's clicks precede the echo of the bat's own signal. Finally, according to the third - masking hypothesis, - the butterfly’s signals can completely mask it, and it turns out to be “invisible” to the bat.
The behavior of a bat in an experiment can indicate which hypothesis is correct. The mouse will either change its flight path, or will try to catch the butterfly and miss, or will not perceive the butterfly at all and will continue to fly.
Behavioral experiments were carried out over seven nights in a soundproof room measuring 5.8 × 4.0 × 3.0 m. The brown leatherback, widespread in America, was used in the experiments. Eptesicus fuscus, belonging to the family of smooth-nosed bats. Experiments were carried out on three individuals E. fuscus.
It was previously shown that all three mice willingly ate the studied species of bear if the butterflies did not make sounds (the absence of acoustic signals was recorded in 22% of the butterflies). Before each experiment, we checked how reliably the mouse caught control butterflies that did not emit signals. We used as control Galleria melonella. After that, every night 16 butterflies (4 - B. trigona, 4 - other species of bears that do not make sound, 8 - G. melonella) were presented to one bat in random order. The butterflies were attached to a thread 60 cm long. The mouse could attack the butterfly several times, but only the first attack was taken into account for analysis.
All experiments were recorded using two high-speed video cameras (250 frames per second). These recordings were analyzed using a computer program (MATLAB), which made it possible to calculate the three-dimensional coordinates of objects in the field of view of the cameras. As a result, the flight vector, the minimum distance between the mouse and the butterfly, and the vector from the mouse to the butterfly at each moment of each interaction were calculated. Angle φ was defined as the angular deviation between the flight vector of the mouse and the vector between the mouse and the butterfly (Fig. 1).
Butterflies B. trigona, like other bears, make clicks with the so-called tymbal organs (see Tymbal). These organs have been well studied in song cicadas, but in butterflies they have a slightly different structure. The timbal sclerites of bear bears have grooves that allow them to generate clicks at a high frequency. A series of clicks are generated both during the active bending of the timbal sclerite inward (active cycle) and during the passive return of the sclerite (passive cycle, Fig. 2). Average interval between clicks B. trigona, equal to 325 μs, turns out to be less than the resolution of the bat's ear (400 μs), so the entire series of clicks is perceived by the mouse as a continuous sound. In Fig. 2 also shows that the frequency spectrum of the butterfly signal amazingly imitates the spectrum of the bat signal.
In behavioral experiments, the authors observed three types of behavior in bats. First, a direct attack, when the mouse flew up and tried to grab the butterfly (Fig. 3A); second, a close attack, where the mouse did not try to grab the butterfly but continued to attack after the butterfly started clicking (Fig. 3B); third, avoidance, where the mouse stopped attacking shortly after the butterfly began clicking and also did not try to grab it (Fig. 3C). The three types of behavior differed in the magnitude of the angle φ (Fig. 3D–F). In the case of a direct attack, the φ values did not exceed the confidence interval of the control attacks. In the close-range attack, φ values decreased or were constant after the butterfly click began, but at the end there was a strong jump exceeding the confidence interval. During avoidance, φ values began to increase immediately after the butterfly began to click.
Mouse echolocation signals also differed in all three cases (Fig. 3G–I). In the case of a direct attack, the signal ended with a typical trill, which was always present in attacks on the control butterfly (Figs. 3G, 4A). The interval between mouse clicks was on average 6 ms. The close-range attack was dominated by regular clicks, occurring at intervals of 10–40 ms, which are typically produced by mice in searching behavior. If a trill was produced, it was very short (Fig. 3H, 4B). During avoidance, the mouse began making infrequent clicks shortly after the butterfly began clicking, and did not trill at all (Figure 4C).
The bat's experience in the experiments was of great importance. Avoidance behavior predominated during the first two nights (Fig. 5), while from nights 3 to 7 close attacks dominated. This suggests that at first the mice were afraid of the clicking butterflies, but then they got used to it. However, only 30% of the attacks were successful, and the attacks were only successful in cases where the butterflies did not click much. This confirms the authors' assumption that butterfly clicks are only effective in jamming mouse signals if they are generated at high frequencies. In close-range attacks, the mouse missed by an average of 16 cm.
These results, according to the authors, are consistent with the predictions of the distance interference hypothesis. The low percentage of avoidances during 3–7 nights suggests that mice do not attempt to evade illusory interference. The mouse approaching the butterfly within a relatively short distance and attempting attacks shows that the butterfly is not completely camouflaged, and therefore the camouflage hypothesis can also be rejected.
It is known that when a bat approaches its prey, the intervals between clicks, the duration and intensity of the signal decrease. These changes in mouse signaling are extremely adaptive. The high click frequency allows the mouse to quickly update its "location information", while the short duration of the signal prevents the signal from overlapping with the echo, which begins to arrive faster as it approaches the victim. In experiments with B. trigona the authors observed the opposite situation: duration of signals and intervals between clicks E. fuscus increased. This reaction of the mouse should make it even more difficult to find a potential victim. The authors compare this behavior with the behavior of other mammals that similarly change their signal in high noise conditions. It has been shown that in this case signal recognition improves.
It is believed that bears originally generated rare clicks to disperse chemicals in order to warn about their inedibility. It is obvious that the evolution of acoustic signaling in butterflies followed the path of improvement of sound organs, in particular the development of grooves on the tymbal membrane and alternate activation of the tymbals, which allowed them to generate clicks with high frequency. As a result, some species (and the authors believe that B. trigona- not the only species of butterfly that can jam the signals of bats) have developed such a wonderful way of protecting themselves from a rather sophisticated predator.
Bats usually live in huge flocks in caves, in which they thrive
navigate in complete darkness. As each mouse flies in and out of the cave, it makes
sounds we cannot hear. Thousands of mice make these sounds at the same time, but this is not
prevents them from perfectly orienting themselves in space in complete darkness and from flying without
colliding with each other. Why can bats fly confidently at full speed?
darkness without bumping into obstacles? The amazing property of these nocturnal animals is
the ability to navigate in space without the help of vision is associated with their ability
emit and detect ultrasonic waves.
It turned out that during flight the mouse emits short signals at a frequency of about 80
kHz, and then receives the reflected echo signals that come to it from the nearest
obstacles and from insects flying nearby.
In order for the signal to be reflected by an obstacle, the smallest linear dimension
This obstacle must be no less than the wavelength of the sound being sent.
The use of ultrasound makes it possible to detect objects smaller than
could be detected using lower audio frequencies. Besides,
the use of ultrasonic signals is due to the fact that as the wavelength decreases
The directionality of radiation is easier to implement, and this is very important for echolocation.
The mouse begins to react to a particular object at a distance of about 1 meter,
at the same time, the duration of the ultrasonic signals sent by the mouse decreases
approximately 10 times, and their repetition rate increases to 100–200 pulses
(clicks) per second. That is, upon noticing an object, the mouse begins to click more often, and
the clicks themselves become shorter. The shortest distance the mouse can
determined in this way is approximately 5 cm.
While approaching the object of hunting, the bat seems to evaluate the angle between
the direction of its speed and the direction towards the source of the reflected signal and
changes the direction of flight so that this angle becomes smaller and smaller.
Can a bat, sending a signal with a frequency of 80 kHz, detect a midge the size
1 mm? The speed of sound in air is taken to be 320 m/s. Explain your answer.
For ultrasonic echolocation, mice use waves with a frequency
1) less than 20 Hz 3) more than 20 kHz
2) from 20 Hz to 20 kHz 4) any frequency
The ability to perfectly navigate in space is associated in bats with their
Dolphin Hearing
Dolphins have an amazing ability to navigate the depths of the sea. This ability is due to the fact that dolphins can emit and receive signals of ultrasonic frequencies, mainly from 80 kHz to 100 kHz. At the same time, the signal power is sufficient to detect a school of fish at a distance of up to a kilometer. The signals sent by the dolphin are a sequence of short pulses with a duration of about 0.01–0.1 ms.
In order for a signal to be reflected by an obstacle, the linear size of this obstacle must be no less than the wavelength of the sent sound. The use of ultrasound can detect smaller objects than could be detected using lower sound frequencies. In addition, the use of ultrasonic signals is due to the fact that the ultrasonic wave has a sharp radiation direction, which is very important for echolocation, and attenuates much more slowly when propagating in water.
The dolphin is also capable of perceiving very weak reflected audio frequency signals. For example, he perfectly notices a small fish that appears from the side at a distance of 50 m.
It can be said that the dolphin has two types of hearing: it can send and receive ultrasonic signals in a forward direction, and it can perceive ordinary sounds coming from all directions.
To receive sharply directed ultrasonic signals, the dolphin has a lower jaw extended forward, through which waves of the echo signal travel to the ear. And to receive sound waves of relatively low frequencies, from 1 kHz to 10 kHz, on the sides of the dolphin’s head, where once upon a time the distant ancestors of dolphins who lived on land had ordinary ears, there are external auditory openings that are almost overgrown, but they allow sounds to pass through Wonderful.
Can a dolphin detect a small fish measuring 15 cm on its side? Speed
sound in water is taken equal to 1500 m/s. Explain your answer.
The ability of dolphins to perfectly navigate in space is associated with their
ability to emit and receive
1) only infrasonic waves 3) only ultrasonic waves
2) only sound waves 4) sound and ultrasonic waves
The dolphin uses for echolocation
1) only infrasonic waves 3) only ultrasonic waves
2) only sound waves 4) sound and ultrasonic waves
Seismic waves
During an earthquake or major explosion, mechanical damage occurs in the crust and thickness of the Earth.
waves, which are called seismic. These waves propagate in the Earth and
can be recorded using special instruments - seismographs.
The operation of a seismograph is based on the principle that a freely suspended load
During an earthquake, the pendulum remains practically motionless relative to the Earth. On
The figure shows a diagram of the seismograph. The pendulum is suspended from the stand, firmly
fixed in the ground, and connected to a pen that draws a continuous line on the paper
belt of a uniformly rotating drum. In case of soil vibrations, stand with drum
also come into oscillatory motion, and a wave graph appears on paper
movements.
There are several types of seismic waves, of which for studying internal
In the structure of the Earth, the most important are the longitudinal wave P and the transverse wave S.
A longitudinal wave is characterized by the fact that particle vibrations occur in the direction
wave propagation; These waves arise in solids, liquids, and gases.
Transverse mechanical waves do not propagate in either liquids or gases.
The speed of propagation of a longitudinal wave is approximately 2 times the speed
propagation of a transverse wave and is several kilometers per second. When
waves P And S pass through a medium whose density and composition change, then the speed
waves also change, which is manifested in the refraction of waves. In denser layers
Earth wave speed increases. The nature of refraction of seismic waves allows
explore the internal structure of the Earth.
Which statement(s) is true?
A. During an earthquake, the weight of the seismograph pendulum oscillates relative to
surface of the Earth.
B. A seismograph installed at some distance from the epicenter of the earthquake,
will first record the seismic P wave, and then the S wave.
Seismic wave P is
1) mechanical longitudinal wave 3) radio wave
2) mechanical transverse wave 4) light wave
The figure shows graphs of the dependence of the velocities of seismic waves on the depth of immersion in the bowels of the Earth. Graph for which of the waves ( P or S) indicates that the Earth's core is not in a solid state? Explain your answer.
Sound Analysis
Using sets of acoustic resonators, you can determine which tones are part of a given sound and what their amplitudes are. This determination of the spectrum of a complex sound is called its harmonic analysis.
Previously, sound analysis was performed using resonators, which are hollow balls of different sizes with an open extension inserted into the ear and a hole on the opposite side. For sound analysis, it is essential that whenever the analyzed sound contains a tone whose frequency is equal to the frequency of the resonator, the latter begins to sound loudly in this tone.
Such methods of analysis, however, are very imprecise and laborious. Currently, they are being replaced by much more advanced, accurate and fast electroacoustic methods. Their essence boils down to the fact that an acoustic vibration is first converted into an electrical vibration, maintaining the same shape, and therefore having the same spectrum, and then this vibration is analyzed by electrical methods.
One of the significant results of harmonic analysis concerns the sounds of our speech. We can recognize a person's voice by timbre. But how do sound vibrations differ when the same person sings different vowels on the same note? In other words, how do the periodic vibrations of air caused by the vocal apparatus differ in these cases with different positions of the lips and tongue and changes in the shape of the oral cavity and pharynx? Obviously, in the vowel spectra there must be some features characteristic of each vowel sound, in addition to those features that create the timbre of a given person's voice. Harmonic analysis of vowels confirms this assumption, namely: vowel sounds are characterized by the presence in their spectra of overtone areas with large amplitude, and these areas always lie at the same frequencies for each vowel, regardless of the height of the sung vowel sound.
Is it possible, using the spectrum of sound vibrations, to distinguish one vowel sound from another? Explain your answer.
Harmonic analysis of sound is called
A. establishing the number of tones that make up a complex sound.
B. establishing the frequencies and amplitudes of the tones that make up a complex sound.
1) only A 2) only B 3) both A and B 4) neither A nor B
What physical phenomenon underlies the electroacoustic method of sound analysis?
1) conversion of electrical vibrations into sound
2) decomposition of sound vibrations into a spectrum
3) resonance
4) conversion of sound vibrations into electrical ones
Tsunami
A tsunami is one of the most powerful natural phenomena - a series of sea waves up to 200 km long, capable of crossing the entire ocean at speeds of up to 900 km/h. The most common cause of tsunamis is earthquakes.
The amplitude of a tsunami, and therefore its energy, depends on the strength of the tremors, on how close the earthquake epicenter is to the bottom surface, and on the depth of the ocean in the area. The wavelength of a tsunami is determined by the area and topography of the ocean floor where the earthquake occurred.
In the ocean, tsunami waves do not exceed 60 cm in height - they are even difficult to detect from a ship or plane. But their length is almost always much greater than the depth of the ocean in which they spread.
All tsunamis are characterized by a large amount of energy that they carry, even in comparison with the most powerful waves generated by wind.
The entire life of a tsunami wave can be divided into four successive stages:
1) generation of a wave;
2) movement across the expanses of the ocean;
3) interaction of the wave with the coastal zone;
4) the collapse of a wave crest onto the coastal zone.
To understand the nature of a tsunami, consider a ball floating on water. When a ridge passes under it, it rushes forward with it, but immediately slides off it, lags behind and, falling into a hollow, moves backward until it is picked up by the next ridge. Then everything is repeated, but not completely: each time the object moves forward a little. As a result, the ball describes a trajectory in the vertical plane that is close to a circle. Therefore, in a wave, a particle of the water surface participates in two movements: it moves along a circle of a certain radius, decreasing with depth, and translationally in the horizontal direction.
Observations have shown that there is a dependence of the speed of wave propagation on the ratio of wavelength and depth of the reservoir.
If the length of the resulting wave is less than the depth of the reservoir, then only the surface layer takes part in the wave motion.
With a wavelength of tens of kilometers for tsunami waves, all seas and oceans are “shallow”, and the entire mass of water takes part in the wave movement - from the surface to the bottom. Friction against the bottom becomes significant. The lower layers (bottom) are strongly slowed down, unable to keep up with the upper layers. The speed of propagation of such waves is determined only by depth. The calculation gives a formula that can be used to calculate the speed of waves on “shallow” water: υ = √gH
Tsunamis travel at a speed that decreases as the depth of the ocean decreases. This means that their length must change as they approach the shore.
Also, when the near-bottom layers slow down, the amplitude of the waves increases, i.e. the potential energy of the wave increases. The fact is that a decrease in wave speed leads to a decrease in kinetic energy, and part of it turns into potential energy. The other part of the decrease in kinetic energy is spent on overcoming the friction force and turns into internal energy. Despite such losses, the destructive power of the tsunami remains enormous, which, unfortunately, we periodically observe in various regions of the Earth.
Why does the amplitude of waves increase when a tsunami approaches the shore?
1) the wave speed increases, the internal energy of the wave is partially converted into kinetic energy
2) the wave speed decreases, the internal energy of the wave is partially converted into potential energy
3) the wave speed decreases, the kinetic energy of the wave is partially converted into potential energy
4) the wave speed increases, the internal energy of the wave is partially converted into potential energy
The movements of a water particle in a tsunami are
1) transverse vibrations
2) the sum of translational and rotational motion
3) longitudinal vibrations
4) only forward movement
What happens to the wavelength of a tsunami as it approaches the shore? Explain your answer.
Human hearing
The lowest tone perceived by a person with normal hearing has a frequency of about 20 Hz. The upper limit of auditory perception varies greatly between individuals. Age is of particular importance here. At the age of eighteen, with perfect hearing, you can hear sound up to 20 kHz, but on average the limits of audibility for any age lie in the range of 18 - 16 kHz. With age, the sensitivity of the human ear to high-frequency sounds gradually decreases. The figure shows a graph of the level of sound perception versus frequency for people of different ages.
The sensitivity of the ear to sound vibrations of different frequencies is not the same. It
responds especially subtly to fluctuations in mid frequencies (in the region of 4000 Hz). As
decrease or increase in frequency relative to the average range of hearing acuity
gradually decreases.
The human ear not only distinguishes sounds and their sources; both ears working together
capable of quite accurately determining the direction of sound propagation. Because the
ears are located on opposite sides of the head, sound waves from the source
sound does not reach them at the same time and acts with different pressures. Due to
even this insignificant difference in time and pressure is determined quite accurately by the brain
direction of the sound source.
Perception of sounds of different volumes and frequencies at 20 and 60 years of age
There are two sound wave sources:
A. A sound wave with a frequency of 100 Hz and a volume of 10 dB.
B. A sound wave with a frequency of 1 kHz and a volume of 20 dB.
Using the graph presented in the figure, determine which sound source
will be heard by man.
1) only A 2) only B 3) both A and B 4) neither A nor B
Which statements made on the basis of the graph (see figure) are true?
A. With age, the sensitivity of human hearing to high-frequency sounds
gradually falls.
B. Hearing is much more sensitive to sounds in the 4 kHz region than to sounds lower or
higher sounds.
1) only A 2) only B 3) both A and B 4) neither A nor B
Is it always possible to accurately determine the direction of sound propagation and
We only hear the rustle of wings, but in fact, a monstrous choir sounds in the underground monastery... Jan Lindblad. In the land of the hoatzins
Can you imagine the terrible noise that would befall you if you suddenly found yourself among thousands of airplanes whose engines were running at full power? It is probably very difficult to imagine such a situation. But let's imagine a little. To begin with, let's assume that you find yourself in a cave full of bats (however, this is not a fantasy yet). Now let’s say that, once in a cave, you suddenly acquired the ability to hear signals in the ultrasonic range, that is, those whose frequency is above 20 kilohertz. If all this happened, you would probably have to endure some pretty unpleasant sensations. You would simply be deafened by the terrible roar, the source of which was the small winged inhabitants of the cave. The fact is that the volume of ultrasonic calls of many species of bats at a distance of 10 centimeters from the animal’s head reaches 110-120 decibels. An aircraft engine produces approximately the same noise, but in the audible frequency range, at a distance of 1 meter. For comparison, it should be noted that a volume level of 130 decibels and above causes pain in a person.
Before explaining the amazing ability of bats to make such a deafening cry, let us recall some properties of ultrasound.
One of the peculiarities of ultrasound is that it can be emitted in a nearly parallel narrow beam, while sounds in the audible range are typically emitted in all directions. This properties of ultrasound can be explained from the point of view of general wave diffraction.
The ability to generate ultrasonic beams allows the signal energy to be focused to a specific location. The intensity of ultrasound increases in proportion to the square of the frequency of vibration, and therefore, by increasing the frequency, it is possible to obtain ultrasounds of enormous strength with relative ease. However, a large amount of ultrasound energy is lost when passing through the medium, and therefore the signal quickly attenuates.
From all that has been said, it is clear why bats are so easily able to emit intense, highly directional signals. It is also clear that signals of lower intensity would be lost in the air, not giving the animals the opportunity to use one of the amazing methods of orientation in space - echolocation.
Bats have long become a classic object for studying animal echolocation, and their “sonars” have become perhaps the most popular topic of various articles and publications about “patents of nature.” The history of the discovery, or rather, research of echolocation goes back almost 200 years and dates back to the 90s of the 18th century.
Lazaro Spallanzani, a professor at the University of the Italian city of Pavia, was no longer young when he first became interested in the ability of nocturnal animals to find their way in the dark. Among his colleagues, the scientist by that time was quite famous for his works in various fields of natural science.
Spallanzani conducted his first experiments in 1793. First, he established that bats move freely in a dark room, in which even such seemingly vigilant nocturnal animals as owls are helpless. Spallanzani decided that the whole secret lies in the extreme visual acuity of bats, allowing them to navigate in complete darkness. To test his assumption, he blinded several bats and released them into the wild. Deprived of vision, the animals flew beautifully and even caught insects.
Spallanzani, confident that bats had a hitherto unknown sense, immediately sent letters to his scientific colleagues asking them to repeat the experiments and inform him about the results. Many of them confirmed the correctness of Spallanzani's research. But the Swiss naturalist Charles Jurin, repeating the experiments described by Spallanzani, did not stop there and took another step towards revealing the secrets of bats. It turned out that if you cover the ears of animals with wax, they: begin to bump into obstacles. Zhurin concluded: bats “see with their ears.”
Flying fox (Pteropus)
Spallanzani checked Zhurin's experiments and, having convinced them of their reliability, came to the conclusion that the bat: a mouse can do just fine without sight, but the loss of hearing inevitably leads it to death. However, Spallanzani was unable to give a convincing explanation for the ability of animals to navigate using hearing. His conclusions were soon rejected and subsequently completely forgotten! Opponents of his ideas, mocking the “auditory” theory, mockingly asked: “if bats see with their ears, then don’t they hear with their eyes?”
The greatest French scientist of that time, Georges Cuvier, having crushed the conclusions of Jurin and Spallanzani, put forward his own speculative theory. In his opinion, the wings of bats are highly sensitive and can detect even the slightest condensation of air that forms between the wing and an obstacle. This hypothesis of Cuvier, called the “tactile theory,” was recognized by many scientists and existed in science for more than 100 years. During this entire period, not a single fresh fact was added to questions concerning the orientation of bats. Despite the fact that some researchers occasionally recalled the concern of the “auditory theory,” their experiments did not go further than those that had already been carried out by Spallanzani and Jurin.
At the beginning of this century, after the tragic incident with the transatlantic liner Titanic, many scientists began to rack their brains to create a device that would provide a signal to the ship when approaching an iceberg. The famous American inventor Hiram Maxim, the one whose name is given to the high-speed machine gun, did not remain aloof from this problem. Maxim was the first to suggest that bats use sound location in flight, and proposed to apply the principle of echolocation in a device for detecting invisible objects. Maxim’s mistake was that he assumed that bats had orientation signals of low infrasonic frequencies, which are not audible to the human ear. The source of such sounds, according to the inventor, could be the flapping wings of animals.
During the First World War, the French physicist Langevin received a patent for the manufacture of a device for detecting underwater objects using an ultrasound generator. In 1920, the English neurophysiologist Hartridge, aware of Langevin's work, hypothesized that the mechanism of echolocation in bats was probably based on the use of ultrasound. However, the hypothesis remained a hypothesis, since no experimental confirmation was made.
The matter finally became clear only in 1938. The decisive role in the discovery was played by the collaboration of representatives of different sciences - physics and biology. Not long before, in the laboratory of the Physics Department at Harvard University, Professor Pierce constructed a device for converting high-frequency sounds into vibrations of a lower frequency audible to the human ear. Having learned about the existence of a sound detector - that was the name of this device - a biology student at the same university, Donald Griffin, one day brought a cage with bats to Pierce's laboratory. These were the small brown bat and the great brown leather bat, widespread in the United States. When the detector's microphone was pointed at the cell, a deafening stream of crackling sounds came from the loudspeaker at the scientists. It has become abundantly clear that bats emit signals in a frequency range that lies above the human hearing threshold.
Pierce's apparatus was designed in such a way that, if necessary, it was possible to establish the frequency distribution of sounds. While conducting research, Griffin and Pierce found that the frequencies of sounds emitted by bats in flight ranged from 30 to 70 kilohertz, and the highest intensity signals reached in the range of 45 to 50 kilohertz. In addition, scientists have found that the animals do not emit sounds continuously, but in the form of short pulses lasting 1-2 milliseconds.
Soon after this, Griffin and Galambos conducted a series of experiments in which they proved that it was possible to deprive a bat of the ability to navigate well among obstacles not only by plugging its ears, but also by tightly closing its mouth. These experiments confirmed the hypothesis once expressed by Hartridge about the presence of ultrasonic signals in bats and their use in orientation in space.
Bats are small, furry animals that expertly dart through the sky as dusk sets in.
Almost all species of bats are nocturnal, resting during the day, hanging upside down, or huddled in some kind of hole.
The bats belong to the order Chiroptera, and make up its main part. It is worth noting that bats live on all continents of our planet, except Antarctica.
It is not realistic to see a mouse in flight; their flapping flight is very different from the flight of birds and insects, surpassing them in maneuverability and aerodynamics.
The average speed of bats in flight is from 20-50 km/h. Their wings have brushes with long fingers connected by a thin but strong leathery membrane. This membrane stretches 4 times without rupture or damage. During flight, the mouse performs symmetrical flapping of its wings, pressing them tightly towards itself, much more tightly than other flying animals, thus improving the aerodynamics of its flight.
The flexibility of the wing allows the Bat to instantly turn 180 degrees, practically without making a turn. Bats are also capable of hover in the air like insects, making rapid flapping of their wings.
Echolocation of Bats
For orientation Bats use echolocation, and not by sight. During flight, they send ultrasonic impulses, which are reflected from various objects, including living ones (insects, birds), and are captured by the ears.
The intensity of ultrasonic signals sent by a mouse is very high, and in many species reaches up to 110-120 decibels (a passing train, a jackhammer). However, the human ear cannot hear them.
Echolocation helps the mouse not only navigate in flight, maneuvering in a dense forest, but also control the flight altitude, hunt, pursue prey, and look for a place to sleep during the day.
The bats They often sleep in groups; despite their small size, they have a high level of socialization.
Songs of the Bats
Among mammals (other than humans), bats are the only ones that use very complex vocal sequences to communicate. This sounds like bird songs, but much more complicated.
Mice sing songs during the courtship of a male with a female, to protect his territory, to recognize each other and indicate his status, when raising cubs. Songs are published in the ultrasonic range; a person can only hear what is “sung” at low frequencies.
In winter, some bats migrate to warmer regions, while others spend the winter by hibernating.
Conservation status of the Bat
All European bat species are protected by many international conventions, including the Berne Convention (conservation of European animals) and the Bonn Convention (conservation of migratory animals). In addition, all of them are listed in the IUCN International Red Book. Some species are considered endangered, and some are considered vulnerable, requiring constant monitoring. Russia has signed all international agreements on the protection of these animals. All species of bats are also protected by domestic legislation. Some of them are included in the Red Book. According to the law, not only the bats themselves, but also their habitats, primarily shelters, are subject to protection. That is why neither the sanitary inspection nor the veterinary authorities simply have the right to take any measures regarding the found settlements of chiropterans in the city, and also, by law, a person does not have the right to destroy the habitats of mouse colonies and the mice themselves.
Interesting facts about Bats
1. There is an international night of bats. This holiday is celebrated on September 21 in order to draw attention to the problems of the survival of these animals. In Russia, this environmental holiday has been celebrated since 2003.
2. In one hour, a bat can eat up to 600 mosquitoes, which, based on the weight of a person, would be equal to about 20 pizzas.
3. Bats are not obese.
4. Bats sing songs at high frequencies.