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Animal echolocation
Animal echolocation
Animal echolocation
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A depiction of the ultrasound signals emitted by a bat, and the echo from a nearby object

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.

Echolocation calls can be frequency modulated (FM, varying in pitch during the call) or constant frequency (CF). FM offers precise range discrimination to localize the prey, at the cost of reduced operational range. CF allows both the prey's velocity and its movements to be detected by means of the Doppler effect. FM may be best for close, cluttered environments, while CF may be better in open environments or for hunting while perched.

Echolocating animals include mammals, especially odontocetes (toothed whales) and some bat species, and, using simpler forms, species in other groups such as shrews. A few bird species in two cave-dwelling bird groups echolocate, namely cave swiftlets and the oilbird.

Some prey animals that are hunted by echolocating bats take active countermeasures to avoid capture. These include predator avoidance, attack deflection, and the use of ultrasonic clicks, which have evolved multiple functions including aposematism, mimicry of chemically defended species, and echolocation jamming.

Early research

[edit]

The term echolocation had been coined by 1944 by the American zoologist Donald Griffin, who, with Robert Galambos, first demonstrated the phenomenon in bats.[1][2] As Griffin described in his book,[3] the 18th century Italian scientist Lazzaro Spallanzani had, by means of a series of elaborate experiments, concluded that when bats fly at night, they rely on some sense besides vision, but he did not discover that the other sense was hearing.[4][5] The Swiss physician and naturalist Louis Jurine repeated Spallanzani's experiments (using different species of bat), and concluded that when bats hunt at night, they rely on hearing.[6][7][8] In 1908, Walter Louis Hahn confirmed Spallanzani's and Jurine's findings.[9]

In 1912, the inventor Hiram Maxim independently proposed that bats used sound below the human auditory range to avoid obstacles.[10] In 1920, the English physiologist Hamilton Hartridge correctly proposed instead that bats used frequencies above the range of human hearing.[11][12]

Echolocation in odontocetes (toothed whales) was not properly described until two decades after Griffin and Galambos' work, by Schevill and McBride in 1956.[13] However, in 1953, Jacques Yves Cousteau suggested in his first book, The Silent World, that porpoises had something like sonar, judging by their navigational abilities.[14]

Principles

[edit]

Echolocation is active sonar, using sounds made by the animal itself. Ranging is achieved by measuring the time delay between the animal's own sound emission and any echoes that return from the environment. The relative intensity of sound received at each ear, as well as the time delay between arrival at the two ears, provide information about the horizontal angle (azimuth) from which the reflected sound waves arrive.[15]

Unlike some human-made sonars that rely on many extremely narrow beams and many receivers to localize a target (multibeam sonar), animal echolocation has only one transmitter and two receivers (the ears) positioned slightly apart. The echoes returning to the ears arrive at different times and at different intensities, depending on the position of the object generating the echoes. The time and loudness differences are used by the animals to perceive distance and direction. With echolocation, the bat or other animal can tell, not only where it is going, but also how big another animal is, what kind of animal it is, and other features.[16][17]

Acoustic features

[edit]

Describing the diversity of echolocation calls requires examination of the frequency and temporal features of the calls. It is the variations in these aspects that produce echolocation calls suited for different acoustic environments and hunting behaviors. The calls of bats have been most intensively researched, but the principles apply to all echolocation calls.[18][19]

Bat call frequencies range from as low as 11 kHz to as high as 212 kHz.[20] Insectivorous aerial-hawking bats, those that chase prey in the open air, have a call frequency between 20 kHz and 60 kHz, because it is the frequency that gives the best range and image acuity and makes them less conspicuous to insects.[21] However, low frequencies are adaptive for some species with different prey and environments. Euderma maculatum, a bat species that feeds on moths, uses a particularly low frequency of 12.7 kHz that cannot be heard by moths.[22]

Echolocation calls can be composed of two different types of frequency structure: frequency modulated (FM) sweeps, and constant frequency (CF) tones. A particular call can consist of one, the other, or both structures. An FM sweep is a broadband signal – that is, it contains a downward sweep through a range of frequencies. A CF tone is a narrowband signal: the sound stays constant at one frequency throughout its duration.[23]

Echolocation calls in bats have been measured at intensities anywhere between 60 and 140 decibels.[24] Certain bat species can modify their call intensity mid-call, lowering the intensity as they approach objects that reflect sound strongly. This prevents the returning echo from deafening the bat.[19] High-intensity calls such as those from aerial-hawking bats (133 dB) are adaptive to hunting in open skies. Their high intensity calls are necessary to even have moderate detection of surroundings because air has a high absorption of ultrasound and because insects' size only provide a small target for sound reflection.[25] Additionally, the so-called "whispering bats" have adapted low-amplitude echolocation so that their prey, moths, which are able to hear echolocation calls, are less able to detect and avoid an oncoming bat.[22][26]

A single echolocation call (a call being a single continuous trace on a sound spectrogram, and a series of calls comprising a sequence or pass) can last anywhere from less than 3 to over 50 milliseconds in duration. Pulse duration is around 3 milliseconds in FM bats such as Phyllostomidae and some Vespertilionidae; between 7 and 16 milliseconds in Quasi-constant-frequency (QCF) bats such as other Vespertilionidae, Emballonuridae, and Molossidae; and between 11 milliseconds (Hipposideridae) and 52 milliseconds (Rhinolophidae) in CF bats.[27] Duration depends also on the stage of prey-catching behavior that the bat is engaged in, usually decreasing when the bat is in the final stages of prey capture – this enables the bat to call more rapidly without overlap of call and echo. Reducing duration comes at the cost of having less total sound available for reflecting off objects and being heard by the bat.[20]

The time interval between subsequent echolocation calls (or pulses) determines two aspects of a bat's perception. First, it establishes how quickly the bat's auditory scene information is updated. For example, bats increase the repetition rate of their calls (that is, decrease the pulse interval) as they home in on a target. This allows the bat to get new information regarding the target's location at a faster rate when it needs it most. Secondly, the pulse interval determines the maximum range that bats can detect objects. This is because bats can only keep track of the echoes from one call at a time; as soon as they make another call they stop listening for echoes from the previously made call. For example, a pulse interval of 100 ms (typical of a bat searching for insects) allows sound to travel in air roughly 34 meters so a bat can only detect objects as far away as 17 meters (the sound has to travel out and back). With a pulse interval of 5 ms (typical of a bat in the final moments of a capture attempt), the bat can only detect objects up to 85 cm away. Therefore, the bat constantly has to make a choice between getting new information updated quickly and detecting objects far away.[28]

Tradeoff between FM and CF

[edit]

FM signal advantages

[edit]
Echolocation call produced by Pipistrellus pipistrellus, an FM bat. The ultrasonic call has been "heterodyned" – multiplied by a constant frequency to produce frequency subtraction, and thus an audible sound – by a bat detector. A key feature of the recording is the increase in the repetition rate of the call as the bat nears its target – this is called the "terminal buzz".

The major advantage conferred by an FM signal is extremely precise range discrimination, or localization, of the target. J. A. Simmons demonstrated this effect with a series of experiments that showed how bats using FM signals could distinguish between two separate targets even when the targets were less than half a millimeter apart. This ability is due to the broadband sweep of the signal, which allows for better resolution of the time delay between the call and the returning echo, thereby improving the cross correlation of the two. If harmonic frequencies are added to the FM signal, then this localization becomes even more precise.[29][30][31]

One possible disadvantage of the FM signal is a decreased operational range of the call. Because the energy of the call is spread out among many frequencies, the distance at which the FM-bat can detect targets is limited.[32] This is in part because any echo returning at a particular frequency can only be evaluated for a brief fraction of a millisecond, as the fast downward sweep of the call does not remain at any one frequency for long.[30]

CF signal advantages

[edit]

The structure of a CF signal is adaptive in that it allows the CF-bat to detect both the velocity of a target, and the fluttering of a target's wings as Doppler shifted frequencies. A Doppler shift is an alteration in sound wave frequency, and is produced in two relevant situations: when the bat and its target are moving relative to each other, and when the target's wings are oscillating back and forth. CF-bats must compensate for Doppler shifts, lowering the frequency of their call in response to echoes of elevated frequency – this ensures that the returning echo remains at the frequency to which the ears of the bat are most finely tuned. The oscillation of a target's wings also produces amplitude shifts, which gives a CF-bat additional help in distinguishing a flying target from a stationary one.[33][29] The horseshoe bats hunt in this way.[34]

Additionally, because the signal energy of a CF call is concentrated into a narrow frequency band, the operational range of the call is much greater than that of an FM signal. This relies on the fact that echoes returning within the narrow frequency band can be summed over the entire length of the call, which maintains a constant frequency for up to 100 milliseconds.[30][32]

Acoustic environments of FM and CF signals

[edit]

An FM component is excellent for hunting prey while flying in close, cluttered environments. Two aspects of the FM signal account for this fact: the precise target localization conferred by the broadband signal, and the short duration of the call. The first of these is essential because in a cluttered environment, the bats must be able to resolve their prey from large amounts of background noise. The 3D localization abilities of the broadband signal enable the bat to do exactly that, providing it with what Simmons and Stein (1980) call a "clutter rejection strategy".[31] This strategy is further improved by the use of harmonics, which, as previously stated, enhance the localization properties of the call. The short duration of the FM call is also best in close, cluttered environments because it enables the bat to emit many calls extremely rapidly without overlap. This means that the bat can get an almost continuous stream of information – essential when objects are close, because they will pass by quickly – without confusing which echo corresponds to which call.[33][29]

A CF component is often used by bats hunting for prey while flying in open, clutter-free environments, or by bats that wait on perches for their prey to appear. The success of the former strategy is due to two aspects of the CF call, both of which confer excellent prey-detection abilities. First, the greater working range of the call allows bats to detect targets present at great distances – a common situation in open environments. Second, the length of the call is also suited for targets at great distances: in this case, there is a decreased chance that the long call will overlap with the returning echo. The latter strategy is made possible by the fact that the long, narrowband call allows the bat to detect Doppler shifts, which would be produced by an insect moving either towards or away from a perched bat.[33][31][29]

Taxonomic range

[edit]

Echolocation occurs in a variety of mammals and birds as described below.[35] It evolved repeatedly, an example of convergent evolution.[29][36]

Tetrapoda

Bats

[edit]
Spectrogram of Pipistrellus pipistrellus bat vocalizations during prey approach. The recording covers a total of 1.1 seconds; lower main frequency c. 45 kHz (as typical for a common pipistrelle). About 150 milliseconds before final contact time between and duration of calls are becoming much shorter ("feeding buzz").
Corresponding audio file:
Pipistrellus calls
Recording of Pipistrellus; echolocation call followed by a social call.
Problems playing this file? See media help.

Echolocating bats use echolocation to navigate and forage, often in total darkness. They generally emerge from their roosts in caves, attics, or trees at dusk and hunt for insects into the night. Using echolocation, bats can determine how far away an object is, the object's size, shape and density, and the direction (if any) that an object is moving. Their use of echolocation, along with powered flight, allows them to occupy a niche where there are often many insects (that come out at night since there are fewer predators then), less competition for food, and fewer species that may prey on the bats themselves.[37]

Echolocating bats generate ultrasound via the larynx and emit the sound through the open mouth or, much more rarely, the nose.[38] The latter is most pronounced in the horseshoe bats (Rhinolophus spp.). Bat echolocation calls range in frequency from 14,000 to well over 100,000 Hz, mostly beyond the range of the human ear (typical human hearing range is considered to be from 20 Hz to 20,000 Hz). Bats may estimate the elevation of targets by interpreting the interference patterns caused by the echoes reflecting from the tragus, a flap of skin in the external ear.[39]

Individual bat species echolocate within specific frequency ranges that suit their environment and prey types. This has sometimes been used by researchers to identify bats flying in an area simply by recording their calls with ultrasonic recorders known as "bat detectors". However, echolocation calls are not always species specific and some bats overlap in the type of calls they use so recordings of echolocation calls cannot be used to identify all bats. Researchers in several countries have developed "bat call libraries" that contain "reference call" recordings of local bat species to assist with identification.[40][41][42]

When searching for prey they produce sounds at a low rate (10–20 clicks/second). During the search phase the sound emission is coupled to respiration, which is again coupled to the wingbeat. This coupling appears to dramatically conserve energy as there is little to no additional energetic cost of echolocation to flying bats.[43] After detecting a potential prey item, echolocating bats increase the rate of pulses, ending with the terminal buzz, at rates as high as 200 clicks/second. During approach to a detected target, the duration of the sounds is gradually decreased, as is the energy of the sound.[44]

Bat evolution

[edit]

Bats evolved at the start of the Eocene epoch, around 64 mya. The Yangochiroptera appeared some 55 mya, and the Rhinolophoidea some 52 mya.[45]

There are two hypotheses about the evolution of echolocation in bats. The first suggests that laryngeal echolocation evolved twice, or more, in Chiroptera, at least once in the Yangochiroptera and at least once in the horseshoe bats (Rhinolophidae):[46]

Chiroptera

Yangochiroptera

 CF  (Early Eocene)
Pteropodidae

fruit bats

Rousettus

tongue‑clicking
Rhinolophoidea

Megadermatidae

horseshoe bats

 FM  (Early Eocene)

The second proposes that laryngeal echolocation had a single origin in Chiroptera, i.e. that it was basal to the group, and was subsequently lost in the family Pteropodidae.[47] Later, the genus Rousettus in the Pteropodidae family evolved a different mechanism of echolocation using a system of tongue-clicking:[48]

Chiroptera

Yangochiroptera

Pteropodidae

fruit bats

Rousettus

tongue‑clicking
CF lost
Rhinolophoidea

Megadermatidae

horseshoe bats

 FM  (Early Eocene)
 CF  (Earliest Eocene)

Calls and ecology

[edit]

Echolocating bats occupy a diverse set of ecological conditions; they can be found living in environments as different as Europe and Madagascar, and hunting for food sources as different as insects, frogs, nectar, fruit, and blood. The characteristics of an echolocation call are adapted to the particular environment, hunting behavior, and food source of the particular bat. The adaptation of echolocation calls to ecological factors is constrained by the phylogenetic relationship of the bats, leading to a process known as descent with modification, and resulting in the diversity of the Chiroptera today.[29][32][31] Bats can inadvertently jam each other, and in some situations they may stop calling to avoid jamming.[49]

Flying insects are a common source of food for echolocating bats and some insects (moths in particular) can hear the calls of predatory bats. However the evolution of hearing organs in moths predates the origins of bats, so while many moths do listen for approaching bat echolocation their ears did not originally evolve in response to selective pressures from bats.[50] These moth adaptations provide selective pressure for bats to improve their insect-hunting systems and this cycle culminates in a moth-bat "evolutionary arms race".[51][52]

Neural mechanisms

[edit]

Because bats use echolocation to orient themselves and to locate objects, their auditory systems are adapted for this purpose, highly specialized for sensing and interpreting the stereotyped echolocation calls characteristic of their own species. This specialization is evident from the inner ear up to the highest levels of information processing in the auditory cortex.[53]

Inner ear and primary sensory neurons
[edit]

Both CF and FM bats have specialized inner ears which allow them to hear sounds in the ultrasonic range, far outside the range of human hearing. Although in most other aspects, the bat's auditory organs are similar to those of most other mammals, certain bats (horseshoe bats, Rhinolophus spp. and the moustached bat, Pteronotus parnelii) with a constant frequency (CF) component to their call (known as high duty cycle bats) do have a few additional adaptations for detecting the predominant frequency (and harmonics) of the CF vocalization. These include a narrow frequency "tuning" of the inner ear organs, with an especially large area responding to the frequency of the bat's returning echoes.[33]

The basilar membrane within the cochlea contains the first of these specializations for echo information processing. In bats that use CF signals, the section of the membrane that responds to the frequency of returning echoes is much larger than the region of response for any other frequency. For example, in the greater horseshoe bat, Rhinolophus ferrumequinum, there is a disproportionately lengthened and thickened section of the membrane that responds to sounds around 83 kHz, the constant frequency of the echo produced by the bat's call. This area of high sensitivity to a specific, narrow range of frequency is known as an "acoustic fovea".[54]

Echolocating bats have cochlear hairs that are especially resistant to intense noise. Cochlear hair cells are essential for hearing sensitivity, and can be damaged by intense noise. As bats are regularly exposed to intense noise through echolocation, resistance to degradation by intense noise is necessary.[55]

Further along the auditory pathway, the movement of the basilar membrane results in the stimulation of primary auditory neurons. Many of these neurons are specifically "tuned" (respond most strongly) to the narrow frequency range of returning echoes of CF calls. Because of the large size of the acoustic fovea, the number of neurons responding to this region, and thus to the echo frequency, is especially high.[56]

Inferior colliculus
[edit]

In the Inferior colliculus, a structure in the bat's midbrain, information from lower in the auditory processing pathway is integrated and sent on to the auditory cortex. As George Pollak and others showed in a series of papers in 1977, the interneurons in this region have a very high level of sensitivity to time differences, since the time delay between a call and the returning echo tells the bat its distance from the target object. While most neurons respond more quickly to stronger stimuli, collicular neurons maintain their timing accuracy even as signal intensity changes.[57] These interneurons are specialized for time sensitivity in several ways. First, when activated, they generally respond with only one or two action potentials. This short duration of response allows their action potentials to give a specific indication of the moment when the stimulus arrived, and to respond accurately to stimuli that occur close in time to one another. The neurons have a very low threshold of activation – they respond quickly even to weak stimuli. Finally, for FM signals, each interneuron is tuned to a specific frequency within the sweep, as well as to that same frequency in the following echo. There is specialization for the CF component of the call at this level as well. The high proportion of neurons responding to the frequency of the acoustic fovea actually increases at this level.[57]

Auditory cortex
[edit]

The auditory cortex in bats is quite large in comparison with other mammals.[58] Various characteristics of sound are processed by different regions of the cortex, each providing different information about the location or movement of a target object. Most of the existing studies on information processing in the auditory cortex of the bat have been done by Nobuo Suga on the mustached bat, Pteronotus parnellii. This bat's call has both CF tone and FM sweep components.[59][60]

Suga and his colleagues have shown that the cortex contains a series of "maps" of auditory information, each of which is organized systematically based on characteristics of sound such as frequency and amplitude. The neurons in these areas respond only to a specific combination of frequency and timing (sound-echo delay), and are known as combination-sensitive neurons.[59][60]

The systematically organized maps in the auditory cortex respond to various aspects of the echo signal, such as its delay and its velocity. These regions are composed of "combination sensitive" neurons that require at least two specific stimuli to elicit a response. The neurons vary systematically across the maps, which are organized by acoustic features of the sound and can be two dimensional. The different features of the call and its echo are used by the bat to determine important characteristics of their prey. The maps include:[59][60]

Auditory cortex of a bat
A FM-FM area
B CF-CF area
C Amplitude-sensitive area
D Frequency-sensitive area
E DSCF area
  • FM-FM area: This region of the cortex contains FM-FM combination-sensitive neurons. These cells respond only to the combination of two FM sweeps: a call and its echo. The neurons in the FM-FM region are often referred to as "delay-tuned", since each responds to a specific time delay between the original call and the echo, in order to find the distance from the target object (the range). Each neuron also shows specificity for one harmonic in the original call and a different harmonic in the echo. The neurons within the FM-FM area of the cortex of Pteronotus are organized into columns, in which the delay time is constant vertically but increases across the horizontal plane. The result is that range is encoded by location on the cortex, and increases systematically across the FM-FM area.[59][61]
  • CF-CF area: Another kind of combination-sensitive neuron is the CF-CF neuron. These respond best to the combination of a CF call containing two given frequencies – a call at 30 kHz (CF1) and one of its additional harmonics around 60 or 90 kHz (CF2 or CF3) – and the corresponding echoes. Thus, within the CF-CF region, the changes in echo frequency caused by the Doppler shift can be compared to the frequency of the original call to calculate the bat's velocity relative to its target object. As in the FM-FM area, information is encoded by its location within the map-like organization of the region. The CF-CF area is first split into the distinct CF1-CF2 and CF1-CF3 areas. Within each area, the CF1 frequency is organized on an axis, perpendicular to the CF2 or CF3 frequency axis. In the resulting grid, each neuron codes for a certain combination of frequencies that is indicative of a specific velocity[56][59][60]
  • Doppler shifted constant frequency (DSCF) area: This large section of the cortex is a map of the acoustic fovea, organized by frequency and by amplitude. Neurons in this region respond to CF signals that have been Doppler shifted (in other words, echoes only) and are within the same narrow frequency range to which the acoustic fovea responds. For Pteronotus, this is around 61 kHz. This area is organized into columns, which are arranged radially based on frequency. Within a column, each neuron responds to a specific combination of frequency and amplitude. This brain region is necessary for frequency discrimination.[56][59][60]

Whales

[edit]
Diagram illustrating sound generation, propagation and reception in a toothed whale. Outgoing sounds are cyan and incoming ones are green.

Biosonar is valuable to both toothed whales (suborder Odontoceti), including dolphins, porpoises, river dolphins, killer whales and sperm whales, and baleen whales (suborder Mysticeti), including right, bowhead, pygmy right, and gray whales and rorquals, because they live in an underwater habitat that has favourable acoustic characteristics and where vision is often extremely limited in range due to absorption or turbidity.[62] Odontocetes are generally able to hear sounds at ultrasonic frequencies while mysticetes hear sounds within the infrasonic frequency regime.[63]

Whale evolution

[edit]

Cetacean evolution consisted of three main radiations. Throughout the middle and late Eocene periods (49–31.5 million years ago), archaeocetes, primitive toothed Cetacea that arose from terrestrial mammals, were the only cetaceans.[64][65] They did not echolocate, but had slightly adapted underwater hearing.[66] By the late middle Eocene, acoustically isolated ear bones had evolved to give basilosaurid archaeocetes directional underwater hearing at low to mid frequencies.[67] With the extinction of archaeocetes at the onset of the Oligocene (33.9–23 million years ago), two new lineages evolved in a second radiation. Early mysticetes (baleen whales) and odontocetes appeared in the middle Oligocene in New Zealand.[65] Extant odontocetes are monophyletic (a single evolutionary group), but echolocation evolved twice, convergently: once in Xenorophus, an Oligocene stem odontocete, and once in the crown odontocetes.[36]

Cetacea
Odontoceti
echolocation

Xenorophus †

late Oligocene
echolocation

Physeteroidea

Ziphiidae, etc.

adaptive radiation

Delphinoidea

Miocene
Oligocene
echolocation

Mysticeti

middle Oligocene
directional u/water hearing

Basilosauridae †

mid/late Eocene
Cetacean evolution timeline[65]
Epoch Start date Event
Miocene 23 mya Adaptive radiation, esp. of dolphins
Oligocene 34 mya Odontocetes echolocation
Eocene 49 mya Archaeocetes underwater hearing

Physical restructuring of the oceans has played a role in the evolution of echolocation. Global cooling at the Eocene-Oligocene boundary caused a change from a greenhouse to an icehouse world. Tectonic openings created the Southern Ocean with a free flowing Antarctic Circumpolar Current.[66][67][68] These events encouraged selection for the ability to locate and capture prey in turbid river waters, which enabled the odontocetes to invade and feed at depths below the photic zone. In particular, echolocation below the photic zone could have been a predation adaptation to diel migrating cephalopods.[67][69] The family Delphinidae (dolphins) diversified in the Neogene (23–2.6 million years ago), evolving extremely specialized echolocation.[70][66]

Four proteins play a major role in toothed whale echolocation. Prestin, a motor protein of the outer hair cells of the inner ear of the mammalian cochlea, is associated with hearing sensitivity.[71] It has undergone two clear episodes of accelerated evolution in cetaceans.[71] The first is connected to odontocete divergence, when echolocation first developed, and the second with the increase in echolocation frequency among dolphins. Tmc1 and Pjvk are proteins related to hearing sensitivity: Tmc1 is associated with hair cell development and high-frequency hearing, and Pjvk with hair cell function.[72] Molecular evolution of Tmc1 and Pjvk indicates positive selection for echolocation in odontocetes.[72] Cldn14, a member of the tight junction proteins which form barriers between inner ear cells, shows the same evolutionary pattern as Prestin.[73] The two events of protein evolution, for Prestin and Cldn14, occurred at the same times as the tectonic opening of the Drake Passage (34–31 Ma) and Antarctic ice growth at the Middle Miocene climate transition (14 Ma), with the divergence of odontocetes and mysticetes occurring with the former, and the speciation of Delphinidae with the latter.[68]

The evolution of two cranial structures may be linked to echolocation. Cranial telescoping (overlap between frontal and maxillary bones, and rearwards displacement of the nostrils[74]) developed first in xenorophids. It evolved further in stem odontocetes, arriving at full cranial telescoping in the crown odontocetes.[75] Movement of the nostrils may have allowed for a larger nasal apparatus and melon for echolocation.[75] This change occurred after the divergence of the neocetes from the basilosaurids.[76] The first shift towards cranial asymmetry occurred in the Early Oligocene, prior to the xenorophids.[76] A xenorophid fossil (Cotylocara macei) has cranial asymmetry, and shows other indicators of echolocation.[77] However, basal xenorophids lack cranial asymmetry, indicating that this likely evolved twice.[76] Extant odontocetes have asymmetric nasofacial regions; generally, the median plane is shifted to the left and structures on the right are larger.[77] Both cranial telescoping and asymmetry likely relate to sound production for echolocation.[75]

Mechanism

[edit]
Southern Alaskan resident killer whales using echolocation

Thirteen species of extant odontocetes convergently evolved narrow-band high-frequency (NBHF) echolocation in four separate events. These species include the families Kogiidae (pygmy sperm whales) and Phocoenidae (porpoises), as well as some species of the genus Lagenorhynchus, all of Cephalorhynchus, and the La Plata dolphin. NBHF is thought to have evolved as a means of predator evasion; NBHF-producing species are small relative to other odontocetes, making them viable prey to large species such as the orca. However, because three of the groups developed NBHF prior to the emergence of the orca, predation by other ancient raptorial odontocetes must have been the driving force for the development of NBHF, not predation by the orca. Orcas, and, presumably ancient raptorial odontocetes such as Acrophyseter, are unable to hear frequencies above 100 kHz.[78]

Another reason for variation in echolocation is habitat. For all sonar systems, the limiting factor deciding whether a returning echo is detected is the echo-to-noise ratio (ENR). The ENR is given by the emitted source level (SL) plus the target strength, minus the two-way transmission loss (absorption and spreading) and the received noise.[79] Animals will adapt either to maximize range under noise-limited conditions (increase source level) or to reduce noise clutter in a shallow and/or littered habitat (decrease source level). In cluttered habitats, such as coastal areas, prey ranges are smaller, and species such as Commerson's dolphin (Cephalorhynchus commersonii) have lowered source levels to better suit their environment.[79]

Toothed whales emit a focused beam of high-frequency clicks in the direction that their head is pointing. Sounds are generated by passing air from the bony nares through the phonic lips. These sounds are reflected by the dense concave bone of the cranium and an air sac at its base. The focused beam is modulated by a large fatty organ known as the melon. This acts like an acoustic lens because it is composed of lipids of differing densities. Most toothed whales use clicks in a series, or click train, for echolocation, while the sperm whale may produce clicks individually. Toothed whale whistles do not appear to be used in echolocation. Different rates of click production in a click train give rise to the familiar barks, squeals and growls of the bottlenose dolphin. A click train with a repetition rate over 600 per second is called a burst pulse. In bottlenose dolphins, the auditory brain response resolves individual clicks up to 600 per second, but yields a graded response for higher repetition rates.[80]

It has been suggested that the arrangement of the teeth of some smaller toothed whales may be an adaptation for echolocation.[81] The teeth of a bottlenose dolphin, for example, are not arranged symmetrically when seen from a vertical plane. This asymmetry could possibly be an aid in sensing if echoes from its biosonar are coming from one side or the other; but this has not been tested experimentally.[82]

Echoes are received using complex fatty structures around the lower jaw as the primary reception path, from where they are transmitted to the middle ear via a continuous fat body. Lateral sound may be received through fatty lobes surrounding the ears with a similar density to water. Some researchers believe that when they approach the object of interest, they protect themselves against the louder echo by quietening the emitted sound. In bats this is known to happen, but here the hearing sensitivity is also reduced close to a target.[83][84]

Oilbirds and swiftlets

[edit]
A Palawan swiftlet (Aerodramus palawanensis) flies in complete darkness inside the Puerto Princesa subterranean river cave.

Oilbirds and some species of swiftlet are known to use a relatively crude form of echolocation compared to that of bats and dolphins. These nocturnal birds emit calls while flying and use the calls to navigate through trees and caves where they live.[85][86]

Terrestrial mammals

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Further information: Shrews § Echolocation

Terrestrial mammals other than bats known or thought to echolocate include shrews,[87][88][89] the tenrecs of Madagascar,[90] Chinese pygmy dormice,[91] and solenodons.[92] Shrew sounds, unlike those of bats, are low amplitude, broadband, multi-harmonic and frequency modulated.[89] They contain no echolocation clicks with reverberations, and appear to be used for simple, close range spatial orientation. In contrast to bats, shrews use echolocation only to investigate their habitat rather than to pinpoint food.[89] There is evidence that blinded laboratory rats can use echolocation to navigate mazes.[93]

Countermeasures

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The especially long tails on the hindwings of the African moon moth, a Saturniid, oscillate in flight, deflecting the hunting bat's attack to the tails and thus enabling the moth to evade capture.[94]

Some insects that are predated by bats have anti-predator adaptations, including predator avoidance,[95] attack deflection,[94] and ultrasonic clicks which appear to function as warnings rather than echolocation jamming.[49][96]

Tiger moths (Arctiidae) of different species (two thirds of the species tested) respond to simulated attack by echolocating bats by producing an accelerating series of clicks. The species Bertholdia trigona has been shown to jam bat echolocation: when pit against naïve big brown bats, ultrasound was immediately and consistently effective at preventing bat attack. Bats came in contact with silent control moths 400% more often than with B. trigona.[97]

Moth ultrasound can also function to startle the bat (a bluffing tactic), warn the bat that the moth is distasteful (honest signalling, aposematism), or mimic chemically defended species. Both aposematism and mimicry have been shown to confer a survival advantage against bat attack.[98][99]

The greater wax moth (Galleria mellonella) takes predator avoidance actions such as dropping, looping, and freezing when it detects ultrasound waves, indicating that it can both detect and differentiate between ultrasound frequencies used by predators and signals from other members of their species.[95] Some members of the Saturniidae moth family, which includes giant silk moths, have long tails on the hindwings, especially those in the Attacini and Arsenurinae subgroups. The tails oscillate in flight, creating echoes which deflect the hunting bat's attack from the moth's body to the tails. The species Argema mimosae (the African moon moth), which has especially long tails, was the most likely to evade capture.[94]

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References

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Further reading

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Animal echolocation

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Animal echolocation, or biosonar, is an active sensory process in which certain animals emit sound pulses and interpret the returning echoes to detect the , , , , and texture of objects in their environment. This mechanism serves as a biological equivalent of , enabling precise navigation, prey detection, and obstacle avoidance in conditions where visual cues are unavailable, such as nocturnal skies, dark caves, or murky aquatic depths. Echolocation has evolved convergently in multiple lineages, with the most advanced forms found in bats and toothed whales (odontocetes). Among the approximately 1,500 bat worldwide, about 70% utilize echolocation, primarily to hunt and orient during flight by producing ultrasonic pulses—frequencies above 20 kHz that are inaudible to humans—via laryngeal mechanisms and detecting echoes with highly sensitive ears. In toothed whales, including dolphins, porpoises, and sperm whales, around 70 employ broadband clicks generated in specialized nasal passages, which are focused forward by a fatty organ known as the and received through the lower jawbone for processing in the . Simpler variants of echolocation occur in other taxa, such as the ultrasonic clicks produced by for short-range habitat assessment and prey location, and the audible snaps or tongue clicks used by cave-dwelling birds like swiftlets and oilbirds to navigate in total darkness. Across these groups, the system's sophistication correlates with ecological demands: bats adapt signal types for cluttered forests or open airspaces, while cetaceans refine pulse trains for target discrimination in three-dimensional volumes. This highlights echolocation's role as a key evolutionary for exploiting sensory niches beyond visual reliance.

Historical Development

Early Observations and Discoveries

The earliest documented observations of animals navigating in darkness without apparent reliance on vision date to ancient Greece, where the philosopher Aristotle noted in the 4th century BCE that bats, despite their small eyes, could fly securely at night and avoid obstacles, implying the use of non-visual senses such as hearing. In the late 18th century, Italian naturalist Lazzaro Spallanzani conducted systematic experiments to investigate bat navigation. In 1793, he blinded several bats by removing their eyes and observed that they continued to fly skillfully, avoiding obstacles like strings and walls in darkened rooms just as effectively as sighted bats, while a blinded owl became disoriented. Spallanzani also plugged the bats' ears with wax, which caused them to crash into objects, leading him to conclude that bats relied primarily on hearing for orientation rather than vision or touch. These findings, detailed in his 1794 publication Lettere sopra il Sospetto di un Nuovo Senso nei Pipistrelli, represented the first scientific demonstration of non-visual sensory navigation in animals, though Spallanzani could not identify the precise mechanism. The concept of echolocation began to emerge in the early . In , British physiologist Hamilton Hartridge proposed that bats emitted high-frequency sound waves—ultrasonics beyond human hearing range—that reflected off objects, allowing the animals to detect obstacles through echoes. Hartridge's , based on bats' observed vocalizations and their navigational prowess in silence or with muffled ears, shifted attention toward acoustic mechanisms, though it lacked direct evidence at the time. Initial empirical confirmation of ultrasonic emissions came in through technological advances. In , physicist G. W. Pierce and biologist Donald R. Griffin used Pierce's newly developed ultrasonic detector—a device incorporating a sensitive to high frequencies and an for visualization—to record faint supersonic pulses from flying bats, with frequencies up to 100 kHz and durations of about 0.003 seconds. These recordings provided the first physical proof of the ultrasonic signals hypothesized by Hartridge, laying the groundwork for understanding echolocation as an active system.

Key Researchers and Milestones

In 1944, American zoologist Donald R. Griffin, drawing inspiration from technologies developed during , conducted experiments that confirmed bats navigate and hunt using ultrasonic pulse-echo mechanisms, a process he termed "echolocation" in a foundational paper co-authored with physicist Robert Galambos. Their work involved training bats to fly in controlled environments while monitoring emitted sounds with early ultrasonic detectors, revealing how echoes from obstacles and prey inform spatial perception. This discovery shifted scientific understanding of animal sensory capabilities, establishing echolocation as a distinct field of study. Building on Griffin's bat research, the 1950s and 1960s saw expanded investigations into cetacean echolocation, with Griffin himself contributing to early observations of sound production in porpoises and dolphins during field and lab studies. Concurrently, psychologist Winthrop N. Kellogg led U.S. Navy-funded experiments on bottlenose dolphins and Atlantic bottlenose porpoises, providing the first direct evidence of echo ranging in marine mammals through obstacle avoidance tasks in darkened pools, as detailed in his 1958 Science publication. These efforts highlighted parallels between bat and cetacean biosonar, influenced by military interest in underwater acoustics. Technological progress in the 1960s, including high-speed tape recorders capable of capturing ultrasonic frequencies and portable sonar devices, facilitated detailed waveform analysis of echolocation calls, enabling researchers to quantify signal duration, frequency, and intensity for the first time. The 1970s and 1980s marked advances in and bioacoustics, with Japanese-American neurobiologist Nobuo Suga pioneering single-neuron recordings in the auditory of mustached bats, identifying specialized "echo-ranging" cells that process delay and Doppler shifts in returning echoes. Suga's mapping of tonotopic and delay-tuned neural circuits laid the groundwork for understanding central processing of biosonar signals. In parallel, biologist Whitlow W. L. Au conducted precise measurements of echolocation clicks in free-ranging and captive dolphins during the 1980s, documenting broadband click spectra up to 120 kHz and beam patterns that optimize target detection in open and shallow waters. A notable recent milestone came in 2024, when a team led by Cynthia F. Moss tracked translocated Kuhl's pipistrelle bats (Pipistrellus kuhlii) using lightweight GPS and acoustic loggers, demonstrating their ability to home over several kilometers relying solely on echolocation—without vision or magnetic cues—via an internalized acoustic of familiar terrain. This study, published in Science, underscored the sophistication of echolocation for large-scale navigation in insectivorous bats.

Physical Principles

Mechanism of Sound Emission and Reflection

Animal echolocation relies on the emission of acoustic pulses, typically in the ultrasonic range, which propagate through the surrounding medium, reflect off environmental objects or targets, and return as echoes to the animal's sensory receptors. These echoes carry encoded in their timing, intensity, and content, allowing the animal to infer spatial properties such as and relative . The process begins with the production of short-duration pulses that minimize overlap between outgoing signals and returning echoes, ensuring clear reception. The fundamental physics of distance estimation follows the time-of-flight principle, where the range dd to an object is calculated as d=v⋅Δt2d = \frac{v \cdot \Delta t}{2}, with vv being the in the medium (approximately 343 m/s in air at standard conditions or 1500 m/s in ) and Δt\Delta t the round-trip time delay between emission and arrival. This assumes a direct path and neglects minor relativistic effects, providing sufficient precision for biological scales where delays are on the order of milliseconds. diminishes with due to geometric spreading, following an (I∝1r2I \propto \frac{1}{r^2}), which sets practical limits on detection range. Several environmental and physical factors influence the reliability of echo interpretation. , the progressive loss of signal energy through absorption and by the medium, is particularly pronounced for high-frequency sounds (20–200 kHz), restricting effective ranges to tens of meters in air and somewhat farther in . The Doppler shift, a change in echo frequency due to relative motion between the emitter, receiver, and target, introduces velocity information but can complicate distance measurements if uncompensated; the shift Δf\Delta f is proportional to the target's speed component toward (Δf≈2vrf0c\Delta f \approx \frac{2 v_r f_0}{c}, where f0f_0 is the emitted and vrv_r the ). Clutter interference arises from unwanted echoes off nearby or irrelevant objects, potentially masking target signals and requiring adaptive emission strategies to resolve. These elements collectively demand high-frequency emissions for fine , as shorter wavelengths enable detection of small features despite the trade-offs in propagation efficiency.

Acoustic Signal Characteristics

Echolocation signals in animals are typically ultrasonic pulses characterized by specific frequencies, durations, and intensities that vary by and . In bats, frequencies often range from 20 to 200 kHz, with durations between 1 and 100 ms and source levels reaching up to 140 dB re 20 μPa at 10 cm. In toothed whales, such as dolphins, signals are clicks with frequencies from 10 to 200 kHz, much shorter durations of about 50 μs (0.05 ms), and intensities up to 226 dB re 1 μPa at 1 m. These parameters enable precise localization of prey and obstacles, with adjustments made based on environmental conditions like clutter or distance. The use of ultrasound provides key advantages for resolution, as the short wavelengths allow echoes to reflect effectively from small targets. The wavelength λ is given by λ = c / f, where c is the (approximately 343 m/s in air or 1500 m/s in ) and f is the ; for a typical at 100 kHz in air, λ ≈ 3.4 mm, sufficient to detect insect-sized objects. This contrasts with longer audible wavelengths, which scatter more and provide poorer detail for fine-scale discrimination. Echolocation signals are directed via specialized anatomical structures to form narrow beams, minimizing loss and interference. In bats, is emitted from the and directed through the or nostrils, producing beams with directionality indices of 10–16 dB and half-power widths around 29°. In cetaceans, clicks originate from phonic lips in the nasal passages and are focused by the fatty , yielding more directional beams with indices up to 32 dB and widths as narrow as 9°. Signal characteristics adapt to propagation challenges in different media: bats employ higher frequencies in air despite greater atmospheric absorption to achieve needed resolution, while cetaceans use comparable ultrasonic ranges in , where absorption is lower, allowing effective transmission over longer distances up to 500 m. For instance, aerial bats balance range and with adjustments, whereas aquatic species like dolphins optimize for reduced impedance mismatches in detecting prey.
ParameterBats (e.g., aerial insectivores)Cetaceans (e.g., dolphins)
Frequency20–200 kHz10–200 kHz
Duration1–100 ms~50 μs
IntensityUp to 140 dB re 20 μPa @ 10 Up to 226 dB re 1 μPa @ 1 m
Beam Width (half-power)~29°~9°

Frequency-Modulated vs. Constant-Frequency Signals

Animal echolocation signals are broadly categorized into frequency-modulated (FM) and constant-frequency (CF) types, each offering distinct acoustic properties suited to different perceptual challenges. FM signals involve a rapid change in frequency over the duration of the pulse, typically sweeping downward in a linear fashion, such as from approximately 80 kHz to 40 kHz in species like the little brown bat (Myotis lucifugus). This broadband structure, with a wide bandwidth B, enables precise range resolution through the time delay of echoes, as the ambiguity in target distance is minimized by the signal's temporal spread across frequencies. The range resolution Δd\Delta d is given by the formula Δd=c2B\Delta d = \frac{c}{2B}, where c is the speed of sound in the medium (approximately 343 m/s in air), highlighting how greater bandwidth in FM signals yields finer spatial discrimination, often on the order of 1-3 cm in bats. In contrast, CF signals maintain a steady throughout much of the duration, exemplified by the tones around 70-90 kHz emitted by horseshoe bats (Rhinolophus ), though specific vary by (e.g., ~83 kHz in the ). These signals excel in detecting target motion and fluttering, such as wing beats in insect prey, by exploiting Doppler shifts and harmonic distortions in the returning echoes, which produce detectable and modulations without requiring broad bandwidth. The long duration of CF components (often 10-60 ms) enhances sensitivity to these subtle velocity-induced changes, allowing for reliable prey identification in less obstructed settings. The choice between FM and CF signals reflects tradeoffs in acoustic performance and environmental adaptation. FM signals provide superior Doppler tolerance and high resolution in cluttered habitats like forests or dense vegetation, where distinguishing closely spaced obstacles is critical, as seen in FM-dominant bats such as Myotis species navigating open woodlands or cluttered understories. CF signals, however, are better suited to edge habitats or open areas with fluttering targets, where motion detection via Doppler effects outweighs the need for fine range acuity, as utilized by CF-FM hybrid emitters like horseshoe bats in semi-open environments. In aquatic media, such as those exploited by cetaceans, signals exhibit lower overall, with broadband clicks that prioritize intensity and directionality over extensive sweeps due to the higher in (~1480 m/s), reducing the relative of higher frequencies and altering resolution dynamics.

Taxonomic Distribution

Bats (Chiroptera)

Bats, belonging to the order Chiroptera, represent one of the most diverse mammalian groups, with 1,500 species recognized globally as of 2025. Echolocation is a prevalent sensory adaptation across this order, enabling precise navigation and prey detection in low-light environments, and is utilized by nearly all species except those in the family Pteropodidae (fruit bats), which primarily depend on vision and olfaction with some passive acoustic listening. Within Chiroptera's two main suborders— and —echolocation is employed universally except in the non-echolocating Pteropodidae of the former, highlighting its foundational role in the order's radiation. The diversity of echolocation in bats is remarkable, particularly among the approximately 70% of species that are , where frequency-modulated constant-frequency (FM-CF) hybrid signals predominate for enhanced target resolution during hunting. These bats are distributed across all continents except polar regions, thriving in temperate forests, tropical rainforests, and arid zones, where echolocation facilitates adaptation to varied habitats. Ecologically, echolocation serves as the primary mechanism for foraging on nocturnal in complete darkness, allowing bats to pursue evasive prey with high accuracy, and for safe through complex systems that serve as roosting sites. However, in indoor environments with smooth walls and unfamiliar structures, echolocation can be disrupted by acoustic mirroring effects, producing confusing or absent echoes that lead to disorientation. A notable exception within fruit bats is the genus Rousettus, such as Rousettus aegyptiacus, which employs crude echolocation via rapid tongue clicks rather than laryngeal sounds, providing basic orientation in dark caves despite lower resolution compared to laryngeal echolocators. This lingual method underscores the convergent adaptations in bat , with echolocation overall underpinning bats' role as key insectivores that regulate pest populations in ecosystems worldwide.

Cetaceans (Whales and Dolphins)

Echolocation is a sensory capability unique to the 79 species of toothed whales (Odontoceti) as of 2025, enabling them to navigate, forage, and communicate in the marine environment, whereas whales (Mysticeti) lack this ability. These odontocetes produce ultrasonic clicks that propagate efficiently through water, reflecting off objects to provide acoustic images of their surroundings. Toothed whales generate echolocation clicks, typically ranging from 10 to 150 kHz, with source levels reaching up to 220 dB re 1 μPa at 1 m, particularly in like sperm whales. These clicks are focused into a directional beam by the fatty structure in the , which acts as an acoustic lens to enhance signal directionality and resolution for target detection. The nature of the signals allows for high-resolution , with peak frequencies varying by —higher in smaller dolphins (up to 150 kHz) and lower in larger whales like sperm whales (around 15 kHz). In practical applications, cetaceans use echolocation to detect schools and other prey at depths exceeding 1 km, as demonstrated by whales during deep foraging dives where they modulate click rates to scan prey layers. whales also produce patterned click sequences known as codas, which facilitate social interactions and may incorporate echolocation-like elements for group coordination during non-foraging activities. This capability supports hunting in low-visibility conditions, such as turbid waters or complete darkness at depth. Dolphins exemplify advanced echolocation applications, such as detecting and extracting prey buried in by increasing click repetition rates while scanning and probing the substrate. Recent research indicates that dolphin echolocation functions more like "touching" with sound—integrating active emission and reception for tactile-like —than passive "seeing," allowing precise interaction with hidden objects. This sensory mode, informed by neural pathways linking auditory processing to motor planning, enhances efficiency in complex benthic environments.

Birds (Oilbirds and Swiftlets)

Among birds, echolocation is a rare adaptation limited to two unrelated families that inhabit dark cave environments: the oilbird (Steatornis caripensis) of the family Steatornithidae and several species of swiftlets in the family Apodidae, genus Aerodramus. This ability has evolved convergently with that in mammals, enabling navigation in complete darkness through the emission of broadband click signals that are audible to humans, unlike the ultrasonic pulses used by most mammalian echolocators. These avian systems provide lower spatial resolution due to the longer wavelengths of their lower-frequency sounds, primarily serving for obstacle avoidance during entry and exit from roosting sites rather than for prey detection or foraging. The , native to caves in northern , produces echolocation signals consisting of short bursts of 2–8 clicks, each lasting less than 10 ms with inter-click intervals of 2–3 ms, and dominant frequencies ranging from 2 to 7 kHz. These audible clicks, generated by rapid vibrations of the (the bird's vocal organ), allow oilbirds to orient in pitch-black interiors where they roost in dense colonies, mapping large obstacles such as walls and stalactites from distances of several meters. The signals' energy is concentrated in the 1.5–2.5 kHz range, aligning with the birds' best hearing sensitivity, though some components extend up to 15 kHz. Swiftlets of the genus Aerodramus, comprising around 26 distributed across and the , exhibit echolocation in at least several cave-nesting forms, with confirmed use in species such as the Himalayan swiftlet (Aerodramus sawarensis). These birds emit brief clicks, often in doublets (two closely spaced pulses), with most acoustic energy between 1 and 10 kHz, typically peaking at 4–8 kHz and occasionally extending to 16 kHz. Like oilbirds, swiftlet clicks are produced via the , facilitating navigation through complex cave systems for nest site location and colony movement, but the coarse resolution limits detection to nearby obstacles and broad spatial features rather than fine-scale prey pursuit.

Other Mammals (Shrews and Tenrecs)

Among terrestrial mammals outside of bats and cetaceans, echolocation is exceptionally rare and confined to a small number of species within the families Soricidae () and Tenrecidae (tenrecs). These animals produce ultrasonic signals primarily through tongue or lip movements, rather than vocalizations from the , enabling short-range orientation in dark, cluttered environments like burrows or leaf litter. These signals often serve dual purposes, aiding both and prey detection while also functioning in communication, such as territorial signaling or social interactions. The ( brevicauda) exemplifies echolocation in , emitting high-frequency ultrasonic clicks centered around 40 kHz to detect prey and navigate tunnels. These clicks, produced by rapid tongue snapping, allow the shrew to locate earthworms and in opaque environments where vision is ineffective, with recordings confirming frequencies between 30 and 50 kHz during activities. Studies have verified that these signals are actively generated for echo-based orientation, distinguishing them from incidental tooth-click artifacts, and they provide critical spatial information in subterranean habitats. In tenrecs, the large-eared tenrec (Geogale aurita), endemic to , employs similar ultrasonic pulses generated by tongue clicks for underground navigation and prey localization. These pulses help detect and other in sandy soils and burrows, supporting the animal's nocturnal, lifestyle in arid southwestern regions. Evidence from comparative acoustic studies indicates that such echolocation in tenrecs, including G. aurita, evolved independently as an adaptation to low-light, complex habitats, with signals serving both exploratory and communicative roles among individuals.

Evolutionary Origins

Convergent Evolution Across Taxa

Echolocation represents a striking example of , where unrelated animal lineages have independently developed similar sensory capabilities to navigate and forage in environments with limited visual cues, such as nocturnal or aquatic habitats. This phenomenon has arisen multiple times across vertebrates, with estimates suggesting at least four to seven independent origins, including in bats (Chiroptera), cetaceans (toothed whales and dolphins), birds (such as oilbirds and swiftlets), and small mammals like and tenrecs. These parallel developments are driven by shared selective pressures, particularly the need for precise orientation and prey detection in low-light or dark conditions, where vision is ineffective. Genetic studies provide compelling evidence for molecular convergence underlying these adaptations. For instance, the gene, known for its role in vocalization and orofacial , shows accelerated evolution in echolocating bats compared to non-echolocating , suggesting its involvement in the neural circuits for sound production and processing in echolocators. Broader genomic analyses reveal parallel amino acid substitutions in over 200 genes between echolocating bats and dolphins, particularly those related to hearing (e.g., Prestin, involved in cochlear amplification) and synaptic function, indicating that similar genetic changes facilitate the independent emergence of biosonar across distant mammalian lineages. These findings highlight how can target conserved genetic pathways to produce analogous traits in response to comparable ecological demands. The fossil record further illustrates the rapid and independent nature of these evolutionary innovations. In bats, the earliest evidence for echolocation dates to approximately 52 million years ago during the Early Eocene, as seen in fossils like Icaronycteris index from the Green River Formation, which exhibit enlarged cochleae adapted for high-frequency sound processing—features absent in the more primitive Onychonycteris finneyi from the same deposits, indicating that flight preceded echolocation in bat evolution. Similar anatomical specializations, such as modified hyoid bones for sound production, appear in the independent histories of other groups, underscoring the repeated co-option of existing structures for sonar-like abilities. Despite these convergences, echolocation systems are constrained by physical principles and environmental differences, leading to taxon-specific adaptations while retaining core features like pulsed emissions to separate outgoing signals from returning echoes. In aerial echolocators like bats and birds, signals are typically high-frequency (20–200 kHz) with short wavelengths for fine resolution, but suffer high absorption and limited range in air; in contrast, aquatic cetaceans use lower-frequency pulses (up to 220 kHz but often 10–100 kHz) that propagate farther in water due to lower absorption and higher sound speed, enabling detection over hundreds of meters.

Phylogenetic Evidence and Timelines

Phylogenetic analyses, combining s, records, and genetic markers, indicate that echolocation has evolved independently in several mammalian and avian lineages, with timelines varying by based on divergence estimates and anatomical evidence. In bats (Chiroptera), molecular clock studies estimate the crown group origin at approximately 64 million years ago (Mya), shortly after the Cretaceous-Paleogene boundary, with early diversification driven by the evolution of flight and sensory adaptations. evidence from the early Eocene (~52-50 Mya), including well-preserved skulls like that of Tanzanycteris from , reveals laryngeal structures consistent with echolocation capabilities, such as enlarged cochleae and modified hyoid bones, suggesting this trait emerged by the Eocene through laryngeal modifications for sound production. The number of origins within bats remains debated, with recent developmental evidence supporting multiple independent acquisitions of laryngeal echolocation, such as in the lineages leading to (e.g., horseshoe bats) and (e.g., most other echolocating bats), and subsequent loss in megabats (Pteropodidae). In cetaceans, particularly odontocetes (toothed whales), the transition to fully aquatic life occurred around 50 Mya during the , following divergence from terrestrial ancestors, as evidenced by fossils like showing intermediate adapted for underwater hearing. Echolocation likely evolved later, around 36-34 Mya in the , after the split from mysticetes ( whales), with phylogenetic reconstructions placing its origin in the last common of extant odontocetes based on molecular divergence times and shared nasal anatomy. This innovation involved the development of phonic lips—specialized nasal valve structures for click production—corroborated by CT scans of fossil skulls like Oligocene Xenorophus, which display asymmetric nasal sacs indicative of early biosonar systems, enabling precise underwater navigation and foraging. Among birds, echolocation is restricted to cave-nesting species like oilbirds (Steatornithidae) and certain swiftlets (Apodidae: Aerodramus), representing independent of mammals. Molecular phylogenies and clock estimates suggest echolocation in swiftlets arose relatively recently, around 20 Mya during the early , coinciding with the radiation of Aerodramus species and their to dark environments, as inferred from cytochrome-b sequence divergences and fossil-calibrated trees showing the split from non-echolocating swiftlets. In oilbirds, a similar timeline (~25-20 Mya) is supported by phylogenetic placement within Caprimulgiformes and syringeal modifications for click production, with no pre- fossil evidence of such traits in avian lineages. Echolocation in other mammals, such as (Eulipotyphla: Soricidae) and tenrecs (Afrotheria: Tenrecidae), has evolved independently through convergent molecular adaptations in these distantly related lineages (diverged ~100 Mya), as evidenced by parallel changes in hearing-related genes like those involved in ultrasonic sensitivity. Genomic analyses provide molecular evidence for click-based echolocation in species such as the common shrew (Sorex araneus) and lesser hedgehog tenrec (Echinops telfairi), suggesting this ability emerged separately in nocturnal or subterranean lineages within each group. Fossil records from the Eocene show proto-insectivore structures compatible with basic biosonar, reinforcing its convergent nature across these clades.

Adaptations to Specific Environments

In aerial environments, bats have evolved echolocation systems optimized for detecting small, fast-moving prey like amid open air spaces. They emit high-frequency pulses, typically in the 20-60 kHz range for most insectivorous species, which allow resolution of targets as small as 1 cm despite the challenges of atmospheric that increases with . During pursuit, bats adjust pulse emission rates dynamically, increasing from 10-20 Hz in search phase to up to 200 Hz in the terminal buzz to track evasive maneuvers with high temporal precision. Aquatic habitats impose different acoustic constraints on cetaceans, favoring adaptations for signal propagation over long distances in , where sound travels faster and farther than in air. Species like sperm whales produce low-frequency clicks (10-30 kHz) that enable echolocation over ranges exceeding several kilometers, ideal for locating deep-sea prey in vast oceanic volumes. Sound production involves specialized air-sac systems in the nasal passages, which recycle air to generate these clicks and facilitate burst-pulse sequences during close-range , achieving inter-click intervals as short as 2-4 ms for fine discrimination. In cluttered cave and subterranean environments, echolocating birds and small mammals rely on low-intensity, multi-harmonic signals suited to short-range navigation amid obstacles like rock walls and tunnels. Oilbirds and swiftlets produce broadband clicks around 7 kHz with multiple harmonics, providing sufficient resolution for collision avoidance within 5-10 meters while minimizing detection by predators in confined, echo-reverberant spaces. Similarly, shrews and tenrecs emit quiet, multi-harmonic pulses (4-8 kHz, 8-16 ms duration) for probing nearby substrates and prey in burrows, where high-intensity signals would cause excessive clutter from reverberations off dense surroundings. Recent 2025 research indicates that cetaceans may employ echolocation for "tactile" echo imaging in murky waters, processing returning signals more akin to touch than vision to discern object textures and shapes in low-visibility conditions like river estuaries.

Physiological Mechanisms

Sound Production Systems

Animals that use echolocation generate acoustic signals through specialized anatomical structures adapted for producing high-frequency sounds suitable for navigating dark or turbid environments. These production systems vary across taxa, reflecting in response to similar ecological pressures, but each is tailored to the animal's and lifestyle. In bats (Chiroptera), echolocation sounds are primarily produced in the using the vocal folds, where air expelled from the lungs causes vibration to generate ultrasonic s. This laryngeal mechanism is powered by a specialized respiratory pump involving the diaphragm and abdominal muscles, enabling precise control over pulse emission. In constant-frequency (CF) bats, such as horseshoe bats, the larynx features hypertrophied intrinsic muscles and reinforced cartilages, allowing sustained high-frequency emissions for Doppler-based target detection. Cetaceans, particularly toothed whales and dolphins, produce echolocation clicks via phonic lips located in the nasal passages, where pressurized air flows across these vibrating tissues to generate pulses. The phonic lips are situated within an asymmetric nasal complex, with the right-side pair often dominant for producing directional clicks that are focused forward by the fatty melon. This nasal-based system contrasts with typical mammalian vocalization and supports high-intensity signals up to 220 dB re 1 μPa for long-range detection. Birds capable of echolocation, including oilbirds (Steatornis caripensis) and certain swiftlets (Aerodramus spp.), generate signals using the , their unique vocal organ at the trachea's bifurcation into the bronchi. Syringeal vibrations, driven by low subglottal pressure, produce short click bursts or double clicks audible to humans, typically in the 1-8 kHz range for navigating cave interiors. This low-pressure mechanism allows integration with other vocalizations without high energy demands. Among other mammals, (Soricidae) and tenrecs (Tenrecidae) employ tongue clicks for echolocation, where rapid tongue snapping against the generates broadband pulses for obstacle avoidance in low-light habitats. These clicks are multifunctional, also aiding in prey detection and manipulation during feeding, as the same oral movements facilitate capturing small . This non-laryngeal system produces lower-intensity sounds compared to bats but suffices for short-range orientation in these small-bodied insectivores.

Auditory Reception and Processing

In echolocating bats, the peripheral features specialized adaptations for detecting faint echoes amid self-generated emissions. The outer ears, or pinnae, are often enlarged relative to body size, enhancing sound collection and providing directional sensitivity through their convoluted shapes that filter and amplify specific frequencies. The is similarly oversized compared to non-echolocating mammals of similar body mass, with a greater number of turns and specialized basilar membrane regions that enable sharp frequency tuning to the ultrasonic ranges of their echolocation calls, typically 20–200 kHz. This tuning results in auditory thresholds as low as 0–10 dB peSPL at peak frequencies, allowing detection of echoes that are substantially weaker than the outgoing pulse. For instance, in species like the (Eptesicus fuscus), cochlear microcircuits are optimized for the downward frequency-modulated sweeps of their calls, providing enhanced sensitivity over three times that of humans at equivalent high frequencies where human hearing declines rapidly above 20 kHz. In cetaceans, such as dolphins and toothed whales, sound reception bypasses traditional external ears due to the aquatic environment, relying instead on specialized structures for underwater echo detection. Incoming echoes are primarily conducted through the lower jaw, where dense mandibular fat bodies—impedance-matched to water—channel vibrations directly to the thin tympanic bone and . From there, the signal reaches the via the oval window, with the exhibiting a pronounced basal enlargement specialized for high-frequency processing. The hair cells in the are densely packed and elongated in the basal turn, supporting sensitivity to ultrasonic frequencies up to 150 kHz or more, far exceeding mammalian norms and enabling precise echo ranging in noisy oceanic conditions. This jaw-mediated pathway minimizes distortion of high-frequency components essential for echolocation. At the neural level, initial echo processing occurs in the (IC) of the , where delay-tuned neurons play a key role in distinguishing echoes from the emitted pulse. These neurons exhibit combination sensitivity, responding vigorously only when an echo follows the emission after a specific delay, effectively subtracting the direct sound through forward masking or inhibitory mechanisms to isolate echo information. In the mustached bat (Pteronotus parnellii), for example, IC neurons are tuned to delays as short as 2–20 ms, corresponding to target distances of 0.3–3 m, with response selectivity sharpened by long-lasting inhibition from the emission that suppresses self-echo interference. This peripheral-to-midbrain processing extracts temporal features like delay and , forming the basis for 3D acoustic mapping without higher cortical involvement at this stage. The fundamental metric for distance estimation is the echo delay τ\tau, given by the equation τ=2dc,\tau = \frac{2d}{c}, where dd is the to the reflecting target and cc is the in the medium (approximately 343 m/s in air or 1480 m/s in ). Delay-tuned neurons in the bat IC directly encode this τ\tau, integrating it with Doppler shifts and intensity cues to construct target location in three dimensions during the initial sensory stages.

Integration with Locomotion and Behavior

In echolocating bats, the timing of sonar pulse emission is closely synchronized with wingbeat cycles to optimize energy efficiency and sensory-motor coordination during flight. This alignment allows bats to emit calls during the upstroke of their wings, minimizing interference from wing-generated noise and facilitating rapid processing of returning amid dynamic aerial maneuvers. A 2024 study on greater horseshoe bats demonstrated that this integration extends to multifaceted tracking strategies, where bats combine echolocation adjustments—such as varying call intensity, direction, and repetition rate—with flight path corrections to maintain precise prey positioning despite sensory delays inherent in ranging. These tactics enable the bats to compensate for propagation times, achieving tracking errors as low as 5-10 cm at approach speeds of up to 4 m/s. Cetaceans, such as bottlenose dolphins and harbor porpoises, integrate echolocation with swimming locomotion through targeted head movements that direct their narrow beams for environmental scanning. During forward propulsion, dolphins exhibit rostrum oscillations—side-to-side and up-down motions—to sweep the beam across potential targets, allowing them to localize prey or obstacles while maintaining streamlined body posture. In porpoises, rolling maneuvers during dives further couple these head scans with body rotations, enabling 360-degree acoustic coverage without disrupting overall swim efficiency. A key behavioral feedback mechanism in echolocation involves dynamic adjustments to call emission rates based on perceived target proximity, forming closed-loop control systems that drive locomotor responses. In bats, as an target is approached within 1-2 meters, the terminal "" phase activates, with pulse repetition rates escalating from 20-50 Hz in the search phase to over 200 Hz, sharpening localization and guiding interceptive dives or turns. This vocal-motor loop integrates auditory feedback from echoes with proprioceptive cues from flight, enabling real-time trajectory refinements. Recent 2025 research on swarming greater mouse-tailed bats (Rhinopoma microphyllum) highlights adaptive echolocation modifications for collision avoidance in dense groups, where ~2,000 individuals emerge simultaneously from roosts. Bats increase call directionality and while spatially dispersing flight paths, reducing acoustic masking from overlapping echoes and increasing average inter-individual distances from ~14 m to ~64 m within 300 m of the to prevent mid-air crashes. Onboard audio-visual recordings revealed that these adjustments occur within seconds of takeoff, with bats prioritizing horizontal separation over vertical clustering to sustain group cohesion without physical contact.

Ecological and Behavioral Applications

Foraging, Navigation, and Social Functions

Echolocating animals employ their systems primarily for , enabling precise detection and pursuit of prey in diverse environments. In bats, such as the (Eptesicus fuscus), echolocation allows foragers to discriminate targets based on echo characteristics reflecting size, shape, and texture; for instance, bats adjust call parameters to resolve fine details like wingbeat patterns or surface irregularities on prey, facilitating targeted attacks during flight. Similarly, horseshoe bats (Rhinolophus ferrumequinum) integrate echo-derived information on prey motion and acoustic features to make adaptive selection decisions, prioritizing larger or more vulnerable in cluttered habitats. Among cetaceans, bottlenose dolphins (Tursiops truncatus) use rapid sequences of broadband clicks to detect and herd fish schools, increasing click emission rates in response to prey sounds and coordinating group by encircling targets to concentrate them for capture. Navigation represents another core application, where echolocation supports orientation over varying distances and in obstructed settings. A 2024 study on Kuhl's pipistrelle bats (*) demonstrated their ability to home over distances of up to 3 kilometers using an acoustic derived solely from echolocation, even when visual and magnetic cues were disrupted, highlighting the system's role in long-range spatial mapping. However, in artificial indoor environments such as buildings, bats can become disoriented due to reverberant echoes and smooth walls that produce weak or disruptive reflections, interfering with obstacle detection and exit location. In birds, oilbirds (Steatornis caripensis) rely on short, clicks to navigate and cave interiors during roosting and fledging, processing echoes to avoid walls and locate nests in complete darkness despite their diurnal visual adaptations. This echolocation enables precise maneuvering through complex, reverberant environments, with calls tuned to the species' hearing sensitivity for effective obstacle avoidance. Social functions of echolocation extend its utility beyond solitary tasks, aiding in individual recognition and group cohesion. In cetaceans like bottlenose dolphins, echolocation complements signature whistles—learned, individually distinctive tonal calls—by allowing acoustic profiling of conspecifics' body shapes and positions for identity verification during encounters at sea. This multimodal approach supports social bonding and coordination in fluid groups. For bats, mother-pup reunions in species such as the Asian particolored bat (Vespertilio sinensis) involve mutual recognition via echolocation calls, where pups preferentially approach their mother's directive pulses amid colony noise, ensuring efficient reunions in large maternity roosts. Pups in Mexican free-tailed bats (Tadarida brasiliensis) similarly respond to adult echolocation signals, though selectivity increases with age. Multifunctionality is evident in , where ultrasonic vocalizations serve dual roles in echolocation and communication. In the (Sorex araneus), twittering calls provide echo-based orientation for habitat assessment at close range while also signaling to conspecifics, blurring the line between sensory and social uses in these small, nocturnal mammals. This overlap allows efficient in energy-limited foragers, with calls yielding both navigational echoes and intraspecific cues.

Predator-Prey Interactions and Countermeasures

In predator-prey interactions involving echolocating animals, prey species have evolved countermeasures to evade detection, while predators adapt their echolocation strategies to overcome these defenses. A prominent example occurs between insectivorous and nocturnal moths, where moths employ active acoustic jamming to disrupt bat . Many moths, particularly in the family Arctiidae, possess tympanal ears that detect incoming bat echolocation calls in the ultrasonic range (typically 20-100 kHz). Upon detection, these moths produce rapid ultrasonic clicks using specialized structures called tymbals, which interfere with the bat's ability to accurately localize and track the prey by creating false echoes or masking the genuine target return. Bats counter this jamming through behavioral adjustments in their echolocation signals. For instance, when faced with moth clicks that overlap in frequency with their calls, bats shift the frequency of their emitted pulses—often increasing or decreasing the peak frequency by several kilohertz—to minimize interference and restore clarity. This spectral jamming avoidance response (JAR) allows bats to maintain effective prey tracking, particularly during the terminal buzz phase of pursuit, where call rates intensify. Such adaptations highlight an , where predator and prey continually refine their acoustic tactics. Similar dynamics appear in marine environments between echolocating dolphins and schooling fish prey. Fish often form tight schools to reduce the detectability of individual members via echolocation, as the overlapping echoes from multiple targets create acoustic clutter that diminishes the prominence of any single echo signature. Studies modeling dense fish schools show that higher densities lead to decreased probability of detecting isolated individuals, with echo overlap complicating target discrimination for dolphins relying on broadband clicks (120-130 kHz). This collective strategy enhances group survival during foraging encounters.

Recent Advances in Field Observations

Recent field observations have advanced our understanding of echolocation in bats through high-resolution tracking technologies. In a 2024 study published in Current Biology, researchers analyzed 3D trajectories of big brown bats (Eptesicus fuscus) pursuing moth prey using synchronized high-speed cameras and microphone arrays. The bats employed a multifaceted strategy integrating three echolocation tactics—increasing call rate, adjusting call intensity, and shifting call direction—and one flight maneuver, a lateral head turn, to compensate for sensory delays and achieve precise prey interception. This integration dramatically improved tracking accuracy, demonstrating how echolocation dynamically couples with flight kinematics in natural foraging scenarios. Innovative cetacean research in 2025 has revealed novel perceptual aspects of echolocation, likening it to a tactile sense. A study led by (WHOI) researchers used advanced brain imaging techniques, including diffusion tensor imaging, to map auditory pathways in echolocating odontocetes like bottlenose dolphins (Tursiops truncatus). The findings indicated that echolocation signals are processed primarily in somatosensory regions of the brain rather than visual areas, suggesting dolphins experience echoes more akin to "touching" distant objects than visualizing them. This tactile-like processing enables fine-grained discrimination of object textures and shapes at ranges up to several meters, as observed in free-swimming dolphins interacting with submerged targets in open-water enclosures. Concurrent 2025 observations of swarms have illuminated collision avoidance mechanisms during mass emergences. Researchers from the Institute for Dynamics and Self-Organization equipped greater mouse-tailed s (Rhinopoma microphyllum) with miniature onboard microphones and accelerometers to record echolocation calls and flight paths as thousands exited a at . The s modulated call timing and to reduce acoustic interference, while spatially spreading out rapidly—achieving near-zero collision rates despite dense formations of approximately 670 individuals per square meter. This adaptive call modulation, combined with subtle flight adjustments, maintained effective echo reception for navigation in cluttered, echo-masked environments. Advancements in acoustic monitoring technology have enhanced 3D localization of bat echolocation in 2025 field studies. A BMC Ecology and Evolution paper introduced the Widefield Acoustics Heuristic (Array WAH), an open-source simulation tool for optimizing designs. Deployed in forested habitats, these arrays—comprising up to 32 synchronized ultrasonic sensors—localized (Myotis daubentonii) calls with sub-meter precision over 50-meter ranges, capturing volumetric call emission patterns during foraging flights. This method has enabled unprecedented insights into spatial echolocation strategies, such as toward prey clusters, without relying on invasive tags.

Bioinspiration and Human Applications

Technological Developments from Echolocation

The discovery of echolocation in bats by Donald R. Griffin and Robert Galambos in the early provided a biological analog to emerging human technologies, demonstrating how high-frequency sound pulses could be used for and detection in low-visibility environments. This work, conducted amid secrecy around and , highlighted natural acoustic sensing principles that paralleled and reinforced the development of these systems for applications, such as submarine detection and aerial surveillance. Griffin's experiments showed bats emitting ultrasonic cries and interpreting echoes to avoid obstacles, inspiring engineers to refine artificial echo-based technologies for greater precision and adaptability. In medical imaging, ultrasound technology draws direct inspiration from the echolocation mechanisms of dolphins, which produce rapid, high-frequency clicks to generate detailed acoustic images of their surroundings for foraging and navigation. Researchers have developed algorithms mimicking dolphin's dual-beam emission—two intertwined ultrasound pulses at slightly offset frequencies—to enhance focusing and resolution in non-invasive scans, reducing artifacts in tissue imaging. For instance, a 2020 study implemented dolphin-inspired biosonar in ultrasound arrays, achieving improved beamforming for sharper diagnostic images of internal structures like tumors or fetal development. This bioinspired approach allows for higher acoustic transparency and gradient-index control, enabling clearer visualization in complex media without increasing energy levels. Bioinspired robotics has advanced through prototypes emulating bat echolocation, particularly for search-and-rescue operations in environments where visual sensors fail, such as smoke-filled buildings or dark caves. In the , engineers at developed the PeAR Bat drone, a compact aerial equipped with ultrasonic transducers that emit frequency-modulated (FM) signals to detect obstacles and map spaces in real time, much like bats adjusting call parameters for dynamic . Funded by a 2025 NSF grant, this prototype uses bio-mimetic sound to autonomously traverse low-light or dusty conditions, potentially reducing response times in disaster scenarios by enabling operation where traditional cameras or are ineffective. Earlier efforts, such as a 2018 , further validated the feasibility of bat-like for obstacle avoidance in unknown terrains. Artificial intelligence applications leverage bat echolocation processing through neural networks designed to interpret echo patterns for , enhancing autonomous systems in challenging conditions. The Bat-G Net, a 2019 convolutional neural network architecture, reconstructs high-resolution 3D images from ultrasonic echoes by training on simulated bat-like scattering data from objects like spheres and cylinders, achieving superior shape discrimination over conventional . This model mimics the bat auditory cortex's ability to extract spatial features from sparse, noisy signals, enabling applications in for real-time detection in darkness or fog. Subsequent adaptations, including 2020 reviews of bat adaptive behaviors, have informed hybrid AI- designs that dynamically adjust signal parameters for improved tracking accuracy in mobile platforms.

Conservation and Research Methodologies

Acoustic monitoring techniques have become essential for assessing echolocation-dependent species in conservation efforts, particularly for bats. Devices such as Anabat systems record ultrasonic echolocation calls, enabling the identification of species and estimation of population densities through analysis of call libraries. The North American Bat Monitoring Program (NABat) employs mobile and stationary acoustic surveys along transects to track bat activity and detect population trends, providing data responsive to environmental changes like white-nose syndrome impacts. These methods yield informative density estimates, with passive surveys demonstrating temporal responsiveness in bat populations across diverse habitats. In bat conservation, wind farm development poses significant risks by disrupting echolocation through increased speeds and operations, leading to reduced acoustic activity. Studies show that activity declines by up to 77% near operating due to -induced alterations in call and . This displacement effect extends to critical resources like sites, where proximity repels and degrades quality. A 2025 study found that in agricultural landscapes impair ' access to water bodies, potentially contributing to declines. To mitigate fatalities, guidelines such as those from the U.S. Fish and Wildlife Service recommend operational curtailment—reducing speeds during low-, high-risk periods—which has shown effectiveness in lowering mortality rates by 50% or more in field studies. Such measures, informed by echolocation monitoring, are integrated into permitting processes. Another 2025 analysis linked complex migration patterns to increased fatalities at sites, highlighting the need for site-specific assessments. For cetaceans, passive acoustic arrays leverage echolocation signals to map migration routes and mitigate ship strikes. Hydrophone networks detect clicks and whistles from species like fin whales, identifying high-risk hotspots along shipping lanes for real-time alerts to vessels. NOAA's Passive Acoustic Monitoring programs use these arrays to monitor distribution changes and evaluate strike risks, supporting protected species assessments in dynamic ocean environments. Automated systems process signals to issue warnings, reducing collision probabilities by integrating with vessel traffic management. Concerns over and altering echolocation detection distances by up to 20% highlight the integration of such data into strategies for aerial and marine species.

References

  1. https://www.cell.com/current-biology/fulltext/S0960-9822(05)00686-X
  2. https://askabiologist.asu.edu/echolocation
  3. https://dnr.maryland.gov/wildlife/pages/plants_wildlife/bats/batelocu.aspx
  4. https://ocean.si.edu/ocean-life/marine-mammals/evolution-echolocation
  5. https://www.historyofinformation.com/detail.php?id=1949
  6. https://www.jstor.org/stable/227600
  7. https://books.google.com/books?id=vObKoQEACAAJ
  8. https://doi.org/10.1113/jphysiol.1920.sp001908
  9. https://nap.nationalacademies.org/read/11429/chapter/11
  10. https://www.science.org/doi/10.1126/science.128.3330.982
  11. https://link.springer.com/chapter/10.1007/978-3-030-97540-1_1
  12. https://www.science.org/doi/10.1126/science.adn6269
  13. https://pmc.ncbi.nlm.nih.gov/articles/PMC10184770/
  14. https://www.americanscientist.org/article/an-acoustic-arms-race
  15. https://www.sciencedirect.com/science/article/pii/B9780444536327002173
  16. https://journals.physiology.org/doi/full/10.1152/physiol.00008.2013
  17. https://www.batcon.org/wp-content/uploads/2020/09/Bat_Echolocation_Research_2nd_Ed_20200918.pdf
  18. https://pmc.ncbi.nlm.nih.gov/articles/PMC2664374/
  19. https://journals.biologists.com/jeb/article/60/1/53/21971/Directional-Sensitivity-of-Echolocation-System-in
  20. https://pubs.aip.org/asa/jasa/article/54/1/157/668592/The-resolution-of-target-range-by-echolocating
  21. https://pubmed.ncbi.nlm.nih.gov/9104033/
  22. https://journals.biologists.com/jeb/article/220/24/4554/18784/Sensing-in-a-noisy-world-lessons-from-auditory
  23. https://pmc.ncbi.nlm.nih.gov/articles/PMC2927269/
  24. https://journals.biologists.com/jeb/article/215/17/2935/10996/Evolution-of-high-duty-cycle-echolocation-in-bats
  25. https://www.batcon.org/1500-reasons-to-love-bats/
  26. https://theconversation.com/fruit-bats-are-the-only-bats-that-cant-and-never-could-use-echolocation-now-were-closer-to-knowing-why-153721
  27. https://animaldiversity.org/accounts/Pteropodidae/
  28. https://animaldiversity.org/accounts/Chiroptera/
  29. https://academic.oup.com/bioscience/article/51/7/557/268230
  30. https://www.pbs.org/wnet/nature/blog/bat-fact-sheet/
  31. https://link.springer.com/chapter/10.1007/978-3-319-25220-9_15
  32. https://www.aaas.org/news/bats-have-vertical-blind-spot-when-using-echolocation
  33. https://royalsocietypublishing.org/doi/10.1098/rspb.2021.1714
  34. https://www.sciencedirect.com/science/article/pii/S235198941400064X
  35. https://www.science.org/doi/10.1126/sciadv.aat8821
  36. https://scholarspace.manoa.hawaii.edu/bitstreams/bd229923-df38-446c-999e-c751f5a139ad/download
  37. https://marinemammalscience.org/science-and-publications/list-marine-mammal-species-subspecies/
  38. https://royalsocietypublishing.org/doi/10.1098/rsos.201598
  39. https://pmc.ncbi.nlm.nih.gov/articles/PMC5720518/
  40. https://www.researchgate.net/publication/272384349_Sperm_whale_echolocation_behaviour_reveals_a_directed_prior-based_search_strategy_informed_by_prey_distribution
  41. https://www.nature.com/articles/s41467-024-47221-8
  42. https://pmc.ncbi.nlm.nih.gov/articles/PMC6894562/
  43. https://pages.ucsd.edu/~johnson/COGS143/Herzing&Santos2011.pdf
  44. https://www.whoi.edu/press-room/news-release/dolphin-sound/
  45. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0323617
  46. https://pmc.ncbi.nlm.nih.gov/articles/PMC3664765/
  47. https://pmc.ncbi.nlm.nih.gov/articles/PMC5451837/
  48. https://birdsoftheworld.org/bow/species/oilbir1/cur/introduction
  49. https://birdsoftheworld.org/bow/species/uniswi1/cur/sounds
  50. https://onlinelibrary.wiley.com/doi/10.1111/j.0908-8857.2004.03182.x
  51. https://www.jstor.org/stable/986137
  52. https://pmc.ncbi.nlm.nih.gov/articles/PMC7262541/
  53. https://www.jstor.org/stable/1380190
  54. https://pubs.aip.org/asa/jasa/article/154/1/411/2903815/Acoustic-behavior-in-the-northern-short-tailed
  55. https://www.afrotheria.net/tenrecs/
  56. https://www.sciencedirect.com/science/article/pii/S0960982220318959
  57. https://www.biorxiv.org/content/10.1101/2023.09.13.556757v1.full-text
  58. https://royalsocietypublishing.org/doi/10.1098/rspb.2006.0200
  59. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0000900
  60. https://www.nature.com/articles/nature12547
  61. https://www.nature.com/articles/nature06549
  62. https://www.researchgate.net/publication/300446337_Echolocation_in_Air_and_Water
  63. https://www.researchgate.net/figure/Molecular-time-scale-for-the-order-Chiroptera-based-on-the-divtime-analyses-11-using_fig1_8051516
  64. https://www.salford.ac.uk/news/50-million-year-old-fossil-skull-uncovers-evolutionary-history-of-bat-echolocation
  65. https://evolution.berkeley.edu/what-are-evograms/the-evolution-of-whales/
  66. https://pubmed.ncbi.nlm.nih.gov/20525610/
  67. https://www.pnas.org/doi/10.1073/pnas.2307340120
  68. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.0908-8857.2004.03182.x
  69. https://bmcecolevol.biomedcentral.com/articles/10.1186/1471-2148-8-102
  70. https://pmc.ncbi.nlm.nih.gov/articles/PMC1919403/
  71. https://journals.biologists.com/jeb/article/202/23/3359/8321/Scaling-of-echolocation-call-parameters-in-bats
  72. https://www.pnas.org/doi/10.1073/pnas.1424457112
  73. https://www.nature.com/articles/srep45517
  74. https://pmc.ncbi.nlm.nih.gov/articles/PMC7480161/
  75. https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2016.00049/full
  76. https://www.aquaticmammalsjournal.org/wp-content/uploads/2010/10/Simard.pdf
  77. https://www.pnas.org/doi/pdf/10.1073/pnas.39.8.884
  78. https://royalsocietypublishing.org/doi/10.1098/rsbl.2009.0378
  79. https://pmc.ncbi.nlm.nih.gov/articles/PMC2781971/
  80. https://www.scientificamerican.com/article/for-dolphins-echolocation-may-be-more-like-touching-than-seeing/
  81. https://pmc.ncbi.nlm.nih.gov/articles/PMC9707786/
  82. https://pmc.ncbi.nlm.nih.gov/articles/PMC7476186/
  83. https://pmc.ncbi.nlm.nih.gov/articles/PMC10851524/
  84. https://pubmed.ncbi.nlm.nih.gov/24133152/
  85. https://pmc.ncbi.nlm.nih.gov/articles/PMC9346347/
  86. https://pubmed.ncbi.nlm.nih.gov/24670659/
  87. https://www.nature.com/articles/s41598-020-58843-5
  88. https://repository.si.edu/bitstream/handle/10088/5115/SCtZ-0027-Lo_res.pdf
  89. https://publish.iupress.indiana.edu/read/how-animals-communicate/section/738384c5-1048-46cf-bcb3-ebe09391dbf2
  90. https://www.science.gov/topicpages/e/echolocation%2Bbehaviour%2Badapted
  91. https://pmc.ncbi.nlm.nih.gov/articles/PMC7892409/
  92. https://pmc.ncbi.nlm.nih.gov/articles/PMC2915923/
  93. https://pubmed.ncbi.nlm.nih.gov/10482752/
  94. https://www.pnas.org/doi/10.1073/pnas.0703550105
  95. https://royalsocietypublishing.org/doi/10.1098/rsos.181076
  96. https://www.sciencedirect.com/science/article/pii/S0960982224007395
  97. https://pmc.ncbi.nlm.nih.gov/articles/PMC5861363/
  98. https://journals.biologists.com/jeb/article/213/1/146/9682/Scanning-sonar-of-rolling-porpoises-during-prey
  99. https://pmc.ncbi.nlm.nih.gov/articles/PMC3178000/
  100. https://bmcbiol.biomedcentral.com/articles/10.1186/s12915-024-02106-6
  101. https://www.pnas.org/doi/10.1073/pnas.2407810122
  102. https://pmc.ncbi.nlm.nih.gov/articles/PMC3079789/
  103. https://pmc.ncbi.nlm.nih.gov/articles/PMC3158933/
  104. https://www.sciencedirect.com/science/article/abs/pii/S0003347204004762
  105. https://pmc.ncbi.nlm.nih.gov/articles/PMC9963516/
  106. https://www.batcon.org/about-bats/bats-in-homes-buildings/
  107. https://pmc.ncbi.nlm.nih.gov/articles/PMC3350692/
  108. https://pmc.ncbi.nlm.nih.gov/articles/PMC9682203/
  109. https://www.sciencedirect.com/science/article/pii/S0003347205809613
  110. https://www.pnas.org/doi/10.1073/pnas.1416679112
  111. https://pmc.ncbi.nlm.nih.gov/articles/PMC9637272/
  112. https://elifesciences.org/articles/55539
  113. https://www.mdpi.com/2410-3888/8/12/580
  114. https://www.cell.com/current-biology/fulltext/S0960-9822(24)00739-5
  115. https://bmcecolevol.biomedcentral.com/articles/10.1186/s12862-025-02441-4
  116. https://direct.mit.edu/books/edited-volume/chapter-pdf/2130973/9780262258852_cak.pdf
  117. https://pubs.aip.org/aip/apl/article/117/17/173701/39109/Physical-implementation-of-dolphin-biosonar-to
  118. https://www.sciencedirect.com/science/article/abs/pii/S2590238524003916
  119. https://www.wpi.edu/news/announcements/professor-nitin-sanket-wins-705k-nsf-grant-advance-bio-inspired-sound-navigation-tiny-robots
  120. https://www.therobotreport.com/wpi-researchers-create-bat-inspired-search-rescue-drones/
  121. https://www.rdworldonline.com/bat-inspired-robot-uses-echolocation-to-navigate/
  122. http://papers.neurips.cc/paper/8629-bat-g-net-bat-inspired-high-resolution-3d-image-reconstruction-using-ultrasonic-echoes.pdf
  123. https://www.mdpi.com/1424-8220/20/10/2958
  124. https://www.nyserda.ny.gov/-/media/Project/Nyserda/Files/Publications/Research/Environmental/Multi-Year-Acoustic-Monitoring-of-Bats.pdf
  125. https://pubs.usgs.gov/publication/tm2C1/full
  126. https://pmc.ncbi.nlm.nih.gov/articles/PMC10883235/
  127. https://www.sciencedirect.com/science/article/pii/S2351989423004171
  128. https://www.sciencedirect.com/science/article/pii/S0006320725000059
  129. https://www.fws.gov/media/voluntary-guidance-avoiding-or-minimizing-wind-turbine-impacts-bats
  130. https://www.batcon.org/press/wandering-migrations-increase-bat-fatalities-at-wind-energy-sites/
  131. https://www.sciencedirect.com/science/article/abs/pii/S0003682X20307544
  132. https://www.fisheries.noaa.gov/s3//2024-05/Passive-Acoustic-Monitoring-Survey-Mitigation-Plan-0.pdf
  133. https://www.sciencedirect.com/science/article/pii/S0964569121003033
  134. https://www.aip.org/scilights/bats-in-the-changing-climate-how-weather-impacts-echolocation
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