Bat. Ultrasound and bats Conservation status of the bat

Bats usually live in huge flocks in caves, in which they can navigate perfectly in complete darkness. Flying in and out of the cave, each mouse makes sounds inaudible to us. Thousands of mice make these sounds at the same time, but this does not prevent them from perfectly orienting themselves in space in complete darkness and flying without colliding with each other. Why can bats fly confidently in complete darkness without bumping into obstacles? Amazing property These nocturnal animals - the ability to navigate in space without the help of vision - is associated with their ability to emit and capture ultrasonic waves.

It turned out that during flight the mouse emits short signals at a frequency of about 80 kHz, and then receives reflected echo signals that come to it from nearby obstacles and from insects flying nearby.

In order for a signal to be reflected by an obstacle, the smallest 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 as the wavelength decreases, the directionality of the radiation is more easily realized, and this is very important for echolocation.

The mouse begins to react to a particular object at a distance of about 1 meter, while the duration of the ultrasonic signals sent by the mouse decreases by about 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 smallest distance a mouse can detect in this way is approximately 5 cm.

While approaching the object of hunting, the bat seems to estimate 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 1 mm midge? The speed of sound in air is taken to be 320 m/s. Explain your answer.

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Beginning of the form

For ultrasonic echolocation, mice use waves with a frequency

1) less than 20 Hz

2) 20 Hz to 20 kHz

3) more than 20 kHz

4) any frequency

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The ability to perfectly navigate in space is associated with bats with their ability to emit and receive

1) only infrasound waves

2) only sound waves

3) only ultrasonic waves

4) sound and ultrasonic waves

Sound recording

The ability to record sounds and then play them back was discovered in 1877 by the American inventor T.A. Edison. Thanks to the ability to record and play back sounds, sound cinema appeared. Recording pieces of music, stories, and even entire plays on gramophone or gramophone records became a popular form of sound recording.

Figure 1 shows a simplified diagram of a mechanical sound recording device. Sound waves from a source (singer, orchestra, etc.) enter speaker 1, in which a thin elastic plate 2, called a membrane, is fixed. Under the influence of a sound wave, the membrane vibrates. The vibrations of the membrane are transmitted to the cutter 3 associated with it, the tip of which draws a sound groove on the rotating disk 4. The sound groove twists in a spiral from the edge of the disk to its center. The figure shows the appearance of sound grooves on a record viewed through a magnifying glass.

The disc on which the sound is recorded is made of a special soft wax material. A copper copy (cliché) is removed from this wax disk using a galvanoplastic method. This involves the deposition of pure copper on the electrode when passing electric current through a solution of its salts. The copper copy is then imprinted onto plastic disks. This is how gramophone records are made.

When playing sound, a gramophone record is placed under a needle connected to the gramophone membrane, and the record is rotated. Moving along the wavy groove of the record, the end of the needle vibrates, and the membrane vibrates along with it, and these vibrations quite accurately reproduce the recorded sound.

When recording sound mechanically, a tuning fork is used. By increasing the playing time of the tuning fork by 2 times

1) the length of the sound groove will increase by 2 times

2) the length of the sound groove will decrease by 2 times

3) the depth of the sound groove will increase by 2 times

4) the depth of the sound groove will decrease by 2 times

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2. Molecular physics

Surface tension

There is a force at work in the world of everyday phenomena around us that is usually not paid attention to. This force is relatively small, its action does not cause powerful effects. However, we cannot pour water into a glass, we cannot do anything at all with this or that liquid without bringing into action forces called surface tension forces. These forces play a significant role in nature and in our lives. Without them, we could not write with a fountain pen; all the ink would immediately pour out of it. It would be impossible to soap your hands because foam would not be able to form. A light rain would have soaked us through. Would be violated water regime soil, which would be disastrous for plants. Would get hurt important functions our body.

The easiest way to grasp the nature of surface tension forces is from a poorly closed or faulty water tap. The drop grows gradually, over time a narrowing is formed - a neck, and the drop breaks off.

The water appears to be enclosed in an elastic bag, and this bag breaks when the force of gravity exceeds its strength. In reality, of course, there is nothing but water in the drop, but the surface layer of water itself behaves like a stretched elastic film.

The same impression is produced by the film of a soap bubble. It looks like the thin stretched rubber of a children's ball. If you carefully place the needle on the surface of the water, the surface film will bend and prevent the needle from sinking. For the same reason, water striders can glide along the surface of the water without falling into it.

In its desire to contract, the surface film would give the liquid a spherical shape, if not for the gravity. The smaller the droplet, the greater the role played by surface tension forces compared to gravity. Therefore, small droplets are close in shape to a ball. During free fall, a state of weightlessness occurs, and therefore raindrops almost strictly spherical. Due to refraction sun rays a rainbow appears in these drops.

The cause of surface tension is intermolecular interaction. Liquid molecules interact with each other more strongly than liquid molecules and air molecules, so the molecules of the surface layer of the liquid tend to get closer to each other and dive deeper into the liquid. This allows the liquid to take a shape in which the number of molecules on the surface would be minimal, and a sphere has the minimal surface area for a given volume. The surface of the liquid contracts and this results in surface tension.

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 quite discomfort. 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 remember some of the 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 you to focus the signal energy into specific place. The intensity of ultrasound increases in proportion to the square of the frequency of vibration, and therefore, by increasing the frequency, ultrasound of enormous strength can be obtained relatively easily. However large number Ultrasonic 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 range of frequencies that lie 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.

A beautiful mythological legend is told by Ovid in “Metamorphoses” about a young nymph who one fine day fell in love with a young and very handsome young man Narcissus. However, he remained indifferent to her and preferred to spend all his time leaning towards the water to admire the reflection of his beautiful image. In the end, he decided to hug his own image, fell into the river and drowned. In despair, the nymph went crazy. Her voice, wandering everywhere, answers all the cries in the forests and mountains.

Ovid, the prisoner of Tomis, did not think that a secret connection would be established between the “echo” of the tender nymph and the nocturnal genus of bats.

The first step was taken by the Italian scientist Lazzaro Spallanzani, who visited the bell tower hundreds of times in the summer of 1783 cathedral in Padua to do extremely interesting experiments with bats hanging in clusters on the dusty ledge of the temple vault. First, he stretched many thin threads between the ceiling and the floor, then he removed several bats, covered their eyes with wax and let them go. The next day I caught bats with their eyes closed and was surprised to notice that their stomach was full of mosquitoes. Therefore, these animals do not need eyes to catch insects. Spallanzani concluded that bats have an unknown seventh sense with which they navigate in flight.

Knowing about Spallanzani's experiments, the Swiss naturalist Charles Jurin decided to cover the ears of bats with wax. He got an unexpected result: the bats were unable to distinguish between surrounding objects and fought against the walls. How can this behavior of bats be explained? Do small animals see with their ears?

The famous French anatomist and paleontologist Georges Cuvier, a highly respected scientist of his time in the field of biology, denied the research of Spallanzani and Jurin and put forward a rather bold hypothesis. Bats, Cuvier said, have a subtle sense of touch, located on the very thin skin of their wings, sensitive to the slightest air pressure that forms between the wings and the obstacle.

This hypothesis has existed in world science for more than 150 years.

In 1912, the inventor of the automatic machine gun, Maxim, quite by accident, put forward the hypothesis that bats orient themselves using the echo received from the noise of their own wings; he proposed to build an apparatus on this principle to warn ships about the approach of icebergs.

The Dutchman S. Dijkgraaf in 1940 and the Soviet scientist A. Kuzyakin in 1946 clearly showed that the organs of touch do not play any role in the orientation of bats and mice. Thus, a hypothesis that existed for 150 years was dispelled. American scientists D. Griffin and R. Galambos were able to provide a genuine explanation for the orientation of bats. Using an ultrasonic detection device, they found that bats make many sounds that are not perceptible to the human ear. They were able to discover and study physical properties"cry" of bats. By inserting special electrodes into the ears of bats, American scientists also determined the frequency of sounds perceived by their hearing. Consequently, the progress of science and technology makes it possible to explain one of exciting secrets nature. It is known that with physical point sound is oscillatory movements, propagating in the form of waves in an elastic medium. The frequency of a sound (hence its pitch) depends on the number of vibrations per second. Human ears perceive air vibrations from 16 to 20,000 Hz. Sounds perceived by humans with a frequency of more than 20,000 Hz are called ultrasounds, and they can be very easily demonstrated using a quartz plate placed under pressure in water. In this case, the noise of the quartz plate is not heard, but the results of its vibration are visible in the form of vortices and even splashes of water. Using quartz, vibrations of up to a billion hertz can be achieved.

Ultrasound is now finding wide application. Using ultrasound, you can detect the smallest cracks or voids in the structure of cast metal parts. It is used instead of a scalpel in bloodless brain surgery and in cutting and grinding ultra-hard parts.

Bats use ultrasound to navigate. Ultrasound is generated by vibration vocal cords. The structure of the larynx is similar to a whistle. The air exhaled by the lungs comes out with high speed and emits a whistle with a frequency of 30,000-150,000 Hz, which is not perceptible to the human ear. The air pressure passing through the bat's larynx is twice the steam pressure of a steam locomotive, which is a great achievement for a small animal.

5-200 sound vibrations occur in the animal’s larynx high frequency(ultrasonic pulses), which usually last only 2-5 thousandths of a second. The brevity of the signal is a very important physical factor: only such a signal can ensure high accuracy of ultrasonic orientation. Sounds emanating from an obstacle located 17 m away return to the bat in approximately 0.1 seconds. If the duration sound signal exceeds 0.1 seconds, the echo reflected by obstacles located at a distance of less than 17 m is perceived by the animal’s ear simultaneously with the sound generating it. Meanwhile, by the time interval separating the end of the signal from the first sounds and echo, the bat determines the distance that separates it from the object that reflected the ultrasound. That's why the beep is so short.

It has been established that the bat, as it approaches an obstacle, increases the number of “signals”. During normal flight, the animal's larynx emits only 8-10 signals per second. However, as soon as the animal detects prey, its flight accelerates, the number of signals emitted reaches 250 per second. This involves “wearing down” the prey by changing the coordinates of the attack. The “location” apparatus of a bat operates simply; and inventive. The animal flies with its mouth open so that the signals it produces are emitted in a cone with an angle of more than 90°. The bat navigates by comparing signals received by its ears, which remain raised throughout the flight, like receiving antennas. Confirmation of this assumption is that if one ear does not work, the bat completely loses the ability to navigate.

All bats of the suborder Microchiroptera (small bats) are equipped with ultrasonic radars various models, which can be divided into three categories: purring, chanting, screaming or frequency modulated mice.

Purring bats live in tropical areas of America and feed on fruits and insects from leaves. Sometimes their purring when searching for midges can be heard by a person if they make sounds at a frequency below 20,000 Hz. And the vampire bat makes the same sounds. Purring "kabbalistic formulas", she searches for wet forests Amazons of exhausted travelers to suck the blood out of them.

Scanning bats that produce staccato sounds are rhinolofii, or horseshoe bats, which are found in the Caucasus and Central Asia; They received this name because of the shape of the folds around the nose. A horseshoe is a loudspeaker that collects sounds into a directed beam. Scanning bats hang upside down and, turning almost in a circle, study the surrounding space with the help of a sound beam. This living detector remains suspended until an insect enters the field of its sound signal. Then the bat makes a lunge to grab the prey. During the hunt, horseshoe bats emit monotonous sounds that are very long compared to their closest relatives (10-20 fractions of a second), the frequency of which is constant and always the same.

Bats in Europe and North America explore the surrounding space using modulated frequency sounds. The tone of the signal and the pitch of the reflected sound are constantly changing. This device makes it much easier to navigate by echo.

In flight, bats of the last two groups behave in a special way. Common bats keep their ears motionless, straight, but bats with a horseshoe nose continuously move their heads and their ears vibrate.

However, the record in the field of orienteering is held by bats that live in areas of America and feed on fish. A fishing bat flies almost at the surface of the water, dives sharply and jumps into the water, lowers its paws with long claws into it and snatches the fish. Such a hunt seems surprising when you consider that only a thousandth of the emitted wave penetrates the water and also a thousandth of the echo energy from the water returns to the bat's locator. If we add to this that part of the wave energy is reflected in fish, the meat of which contains a large amount of water, one can understand what a negligible fraction of the energy reaches the animal’s ear and what fantastic accuracy its sound organ must have. One can also add that such a very weak wave must still be distinguished from the sound background of a lot of interference.

70 million years of existence of bats on earth taught them to use physical phenomena, which are still unknown to us. Finding a signal returned to its source, significantly attenuated and drowned in interference noise, is technical problem, which occupies the minds of scientists to the highest degree. True, man has at his disposal an amazing detector using radio waves, the so-called radar, which over the quarter century of its existence has performed miracles, culminating in the sounding of the Moon and precise measurement orbit of the planet Venus. What would aviation do without radar? navy, air defense, geographers, meteorologists, glaciologists of the white continents? And yet radio engineers dream of a bat-ultrasonic radar, undoubtedly more advanced than the one invented by man. The small creature knows how to select and amplify the negligible residual fraction of the signal sent among the ocean of interference. Faced with extremely high noise, called crazy ether, engineers and technicians would be lucky if they could use the signal-trapping principles of bats. While radar remains a brilliant detector for long distances, echo-based bat locator remains the ideal remedy for short distances.

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 species 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 more ancient way defense known in some butterflies - when acoustic signaling is accompanied by secretion chemicals, scaring off a 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, and different types they do it differently. 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 records were analyzed using 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 inward bending of the timbal sclerite (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. For close-range attacks, φ values ​​decreased or remained 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 search 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 experiments had great value. 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 at 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. Low percentage avoidance for 3–7 nights suggests that mice do not try 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 rate allows the mouse to quickly update its "location information", while the short duration of the click 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 to the behavior of other mammals that similarly change their signal in high-noise environments. 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 timbal 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.

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, this is not true.

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 big 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.