Echolocation jamming

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Echolocation (or sonar) systems of animals, like human radar systems, are susceptible to interference known as echolocation jamming or sonar jamming. Jamming occurs when non-target sounds interfere with target echoes. Jamming can be purposeful or inadvertent, and can be caused by the echolocation system itself, other echolocating animals, prey, or humans. Echolocating animals have evolved to minimize jamming, however; echolocation avoidance behaviors are not always successful.

Contents

Self jamming

Echolocating animals can jam themselves in a number of ways. Bats, for example, produce some of the loudest sounds in nature, [1] and then they immediately listen for echoes that are hundreds of times fainter than the sounds they emit. [2] To avoid deafening themselves, whenever a bat makes an echolocation emission, a small muscle in the bat's middle ear (the stapedius muscle) clamps down on small bones called ossicles, which normally amplify sounds between the ear drum and the cochlea. [3] This dampens the intensity of the sounds that the bat hears during this time, preserving hearing sensitivity to target echoes.

Jamming can occur if an animal is still producing a sound when an echo returns, for example, from a nearby object. Bats avoid this type of jamming by producing short sounds of 3–50 ms when searching for prey or navigating. [4] Bats produce progressively shorter sounds, down to 0.5 ms, to avoid self-jamming when echolocating targets that they are approaching. [5] This is because echoes from nearby targets will return to the bat sooner than sounds from distant targets.

Another form of jamming occurs when an echolocating animal produces many sounds in succession and assigns an echo to the wrong emission. To avoid this type of jamming, bats typically wait enough time for echoes to return from all possible targets before making the next sound. This can be seen clearly when a bat attacks an insect. The bat produces sounds with progressively shorter time intervals, but always allowing enough time for sounds to travel to the target and back. [6] Another way bats overcome this problem is by producing successive sounds with unique time-frequency structures. [7] This allows bats to process echoes from multiple emissions at the same time, and to correctly assign an echo to its emission using its time-frequency signature.

Jamming by other echolocation systems

Like electric fish, echolocating animals are susceptible to jamming from other animals of the same species emitting signals in the nearby environment. [8] To avoid such jamming, bats use a strategy also employed by electric fish to avoid this jamming: a behavior known as jamming avoidance response (JAR). [8] In a JAR, one or both animals change the frequency of their sounds away from that used by the other animal. [8] [9] This has the effect of allowing each animal a unique frequency bandwidth where jamming will not occur. Bats can make this adjustment very rapidly, often in less than 0.2 seconds. [9]

Big brown bats can avoid jamming by going silent for periods of time when following another echolocating big brown bat. [10] This sometimes allows the silent bat to capture a prey in competitive foraging situations.

Jamming by prey

The moth Bertholdia trigona is one of several moth species known to jam the echolocation of its predator Bertholdiatrigona.jpg
The moth Bertholdia trigona is one of several moth species known to jam the echolocation of its predator

Many tiger moths produce ultrasonic clicks in response to the echolocation calls bats use while attacking prey. [11] For most species of tiger moth these clicks warn bats that the moths have toxic compounds that make them distasteful. [12] However, the tiger moth Bertholdia trigona produces clicks at a very high rate (up to 4,500 per second) to jam bat echolocation. [13] Jamming is the most effective defense against bats ever documented, with jamming causing a ten-fold decrease in bat capture success in the field. [14]

History

The possibility that moths jam bat echolocation arose with an experiment report published in 1965 by Dorothy Dunning and Kenneth Roeder. [15] Moth clicks were played through a loudspeaker as bats tried to capture mealworms catapulted through the air. Moth clicks caused bats to veer away from the mealworms, but echolocation calls played through the speaker did not, causing the authors to conclude that the moth clicks themselves dissuaded the bats. However, it was later determined that the moth clicks were played at an unnaturally loud level, invalidating this conclusion. [16]

In subsequent years Dunning conducted further experiments to show that moth clicks serve a warning function. [16] That is, they communicate to bats that the moths are toxic, as many moths accumulate toxic chemicals from their host plants as caterpillars and keep them in their tissues through adulthood. Roeder agreed with Dunning's findings. [17]

James Fullard and colleagues published findings in 1979, [18] and 1994 [19] arguing in favor of the jamming hypothesis based on the acoustic characteristics of moth clicks, however this hypothesis was still widely debated in the literature during that time. [12] [20] [21]

In the 1990s experiments were conducted broadcasting clicks to bats performing echolocation tasks on a platform [22] and with neurophysiological methods [23] to demonstrate a plausible mechanism for jamming. The researchers concluded that most tiger moths do not produce enough sound to jam bat sonar.

The first study to conclusively demonstrate that moths jam bats was published in 2009 by researchers at Wake Forest University. [13] In this study big brown bats were raised in captivity to ensure they had no prior experience with clicking prey and trained to attack moths tethered to a thin line attached to the ceiling in an indoor flight room. Over a nine-night experiment the bats attacked non-clicking control moths and clicking Bertholdia trigona – moths that were selected for their extraordinary clicking abilities. Bats had substantial difficulty catching the clicking moths compared to silent controls, and ate the B. trigona moths when they had the opportunity, thus refuting the hypothesis that the clicks were warning the bats of moths' toxicity. Moth clicks also disrupted the stereotypical pattern of the bats echolocation, confirming the clicks' jamming function.

Since then, sonar jamming has been documented in two other moth families. Silk moths (Saturniidae) have elongated hindwing tails that reflect bat sonar, increasing the success of escape from bat attacks. [24] Some species of hawkmoths (Sphingidae) produce ultrasound capable of sonar jamming. [25] Sonar jamming capability has evolved independently in at least six subfamilies. [26] Because sonar jamming seems to require high duty cycle ultrasound, it is believed to be a derived form of the simpler ultrasound used for aposematism and mimicry. [27]

In a 2022 report, bats are found to change their emission lengths to defeat high duty cycle jamming. [28]

Humans jamming animals

Humans may jam echolocating animals deliberately or accidentally. Recent efforts have been made to develop acoustic jamming deterrents to exclude bats from buildings or bridges, or to keep bats away from wind turbines where large numbers of mortalities occur. [29] These deterrents have been shown to reduce bat activity over a small area. However, scaling up acoustic deterrents to large volumes for applications such as keeping bats away from wind turbines is difficult because of the high atmospheric attenuation of ultrasound.

Related Research Articles

<span class="mw-page-title-main">Ultrasound</span> Sound waves with frequencies above the human hearing range

Ultrasound is sound with frequencies greater than 20 kilohertz. This frequency is the approximate upper audible limit of human hearing in healthy young adults. The physical principles of acoustic waves apply to any frequency range, including ultrasound. Ultrasonic devices operate with frequencies from 20 kHz up to several gigahertz.

<span class="mw-page-title-main">Animal echolocation</span> Method used by several animal species to determine location using sound

Echolocation, also called bio sonar, is a biological active sonar used by several animal groups, both in the air and underwater. Echolocating animals emit calls and listen to the echoes of those calls that return from various objects near them. They use these echoes to locate and identify the objects. Echolocation is used for navigation, foraging, and hunting prey.

<span class="mw-page-title-main">Microbat</span> Suborder of mammals

Microbats constitute the suborder Microchiroptera within the order Chiroptera (bats). Bats have long been differentiated into Megachiroptera (megabats) and Microchiroptera, based on their size, the use of echolocation by the Microchiroptera and other features; molecular evidence suggests a somewhat different subdivision, as the microbats have been shown to be a paraphyletic group.

<span class="mw-page-title-main">Arctiinae</span> Subfamily of moths

The Arctiinae are a large and diverse subfamily of moths with around 11,000 species found all over the world, including 6,000 neotropical species. This subfamily includes the groups commonly known as tiger moths, which usually have bright colours, footmen, which are usually much drabber, lichen moths, and wasp moths. Many species have "hairy" caterpillars that are popularly known as woolly bears or woolly worms. The scientific name Arctiinae refers to this hairiness. Some species within the Arctiinae have the word "tussock"' in their common names because they have been misidentified as members of the Lymantriinae subfamily based on the characteristics of the larvae.

Human echolocation is the ability of humans to detect objects in their environment by sensing echoes from those objects, by actively creating sounds: for example, by tapping their canes, lightly stomping their foot, snapping their fingers, or making clicking noises with their mouths. People trained to orient by echolocation can interpret the sound waves reflected by nearby objects, accurately identifying their location and size.

<span class="mw-page-title-main">Batesian mimicry</span> Bluffing imitation of a strongly defended species

Batesian mimicry is a form of mimicry where a harmless species has evolved to imitate the warning signals of a harmful species directed at a predator of them both. It is named after the English naturalist Henry Walter Bates, who worked on butterflies in the rainforests of Brazil.

In evolutionary biology, an evolutionary arms race is an ongoing struggle between competing sets of co-evolving genes, phenotypic and behavioral traits that develop escalating adaptations and counter-adaptations against each other, resembling the geopolitical concept of an arms race. These are often described as examples of positive feedback. The co-evolving gene sets may be in different species, as in an evolutionary arms race between a predator species and its prey, or a parasite and its host. Alternatively, the arms race may be between members of the same species, as in the manipulation/sales resistance model of communication or as in runaway evolution or Red Queen effects. One example of an evolutionary arms race is in sexual conflict between the sexes, often described with the term Fisherian runaway. Thierry Lodé emphasized the role of such antagonistic interactions in evolution leading to character displacements and antagonistic coevolution.

<span class="mw-page-title-main">Brown long-eared bat</span> Species of bat

The brown long-eared bat or common long-eared bat is a small Eurasian insectivorous bat. It has distinctive ears, long and with a distinctive fold. It is extremely similar to the much rarer grey long-eared bat which was only validated as a distinct species in the 1960s. An adult brown long-eared bat has a body length of 4.5–4.8 cm, a tail of 4.1–4.6 cm, and a forearm length of 4–4.2 cm. The ears are 3.3–3.9 cm in length, and readily distinguish the long-eared bats from most other bat species. They are relatively slow flyers compared to other bat species.

<span class="mw-page-title-main">Crypsis</span> Aspect of animal behaviour and morphology

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<i>Cycnia tenera</i> Species of moth

Cycnia tenera, the dogbane tiger moth or delicate cycnia, is a moth in the family Erebidae. It occurs throughout North America, from southern British Columbia to Nova Scotia southwards to Arizona and Florida. The species is distasteful and there is evidence that it emits aposematic ultrasound signals; these may also jam bat echolocation, as the functions are not mutually exclusive.

Whispering is an unvoiced mode of phonation in which the vocal cords are abducted so that they do not vibrate; air passes between the arytenoid cartilages to create audible turbulence during speech. Supralaryngeal articulation remains the same as in normal speech.

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James A. Simmons is a pioneer in the field of biosonar. His research includes behavioral and neurophysiological studies of sound processing in the echolocating bat. From the time he began graduate research in the late 1960s to the present, he has been in the forefront of bat echolocation research. Simmons was honored as a fellow of the Acoustical Society of America (ASA) in 1996 and of the American Association for the Advancement of Science in 2000. He was awarded the ASA's second Silver Medal in Animal Bioacoustics in 2005. His current position is Professor in the Department of Neuroscience, Brown University.

<span class="mw-page-title-main">Bat</span> Order of flying mammals

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Ultrasound avoidance is an escape or avoidance reflex displayed by certain animal species that are preyed upon by echolocating predators. Ultrasound avoidance is known for several groups of insects that have independently evolved mechanisms for ultrasonic hearing. Insects have evolved a variety of ultrasound-sensitive ears based upon a vibrating tympanic membrane tuned to sense the bat's echolocating calls. The ultrasonic hearing is coupled to a motor response that causes evasion of the bat during flight.

<span class="mw-page-title-main">Daubenton's bat</span> Species of bat

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<span class="mw-page-title-main">Deimatic behaviour</span> Bluffing display of an animal used to startle or scare a predator

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<span class="mw-page-title-main">Akito Y. Kawahara</span> Entomologist

Akito Y. Kawahara is an American and Japanese entomologist, scientist, and advocate of nature education, and the son of the modern conceptual artist On Kawara.

Annemarie Surlykke was a Danish physiologist. She contributed significantly to bioacoustic research, in particular in the fields of insect hearing and acoustic communication, bat echolocation and insect-bat interactions. Graduated from University of Southern Denmark, employments at University of Tübingen and Aarhus University. From 1987 associate professor at University of Southern Denmark, full professor in 2011.

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