Editing Animal echolocation

{{good article}}
{{short description |Method used by several animal species to determine location using sound}}
[[File:Animal echolocation.svg|thumb|upright=1.8|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 [[Echo (phenomenon) |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 [[animal navigation |navigation]], [[foraging]], and [[predation|hunting prey]].

Echolocation calls can be [[Frequency modulation|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 [[mammal]]s, especially [[odontocetes]] (toothed whales) and some [[bat]] species, and, using simpler forms, species in other groups such as [[shrew]]s. A few bird species in two cave-dwelling bird groups echolocate, namely [[cave swiftlet]]s and the [[oilbird]]. 

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

== Early research ==

The term ''echolocation'' was coined by 1944<!--perhaps as early as 1938--> by the American zoologist [[Donald Griffin]], who, with [[Robert Galambos]], first demonstrated the phenomenon in bats.<ref>{{cite web |last=Yoon |first=Carol Kaesuk |url=https://www.nytimes.com/2003/11/14/nyregion/donald-r-griffin-88-dies-argued-animals-can-think.html |title=Donald R. Griffin, 88, Dies; Argued Animals Can Think |work=[[The New York Times]] |date=14 November 2003 |archive-url=https://archive.today/20120915122729/http://www.nytimes.com/2003/11/14/nyregion/donald-r-griffin-88-dies-argued-animals-can-think.html |archive-date=15 September 2012 |url-status=live }}</ref><ref name="Griffin 1944">{{cite journal |last=Griffin |first=Donald R. |author-link=Donald Griffin |title=Echolocation by Blind Men, Bats and Radar |journal=Science |volume=100 |issue=2609 |pages=589–590 |date=December 1944 |pmid=17776129 |doi=10.1126/science.100.2609.589 |bibcode=1944Sci...100..589G }}</ref> As Griffin described in his book,<ref>{{cite book |last=Griffin |first=Donald R. |author-link=Donald Griffin |year=1958 |title=Listening in the dark |url=https://archive.org/details/listeningindarka00dona |url-access=registration |publisher=Yale University Press}}</ref> 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.<ref>{{cite book |last=Spallanzani |first=Lazzaro |author-link=Lazzaro Spallanzani |url=https://books.google.com/books?id=nYucKchNzIwC&pg=PA1 |title=Lettere sopra il sospetto di un nuovo senso nei pipistrelli |trans-title=Letters on the suspicion of a new sense in bats |language=it |location=Turin, Italy |publisher=Stamperia Reale |date=1794 }}</ref><ref>{{cite journal |last=Dijkgraaf |first=Sven |date=March 1960 |title=Spallanzani's unpublished experiments on the sensory basis of object perception in bats |journal=Isis |volume=51 |issue=1 |pages=9–20 |doi=10.1086/348834 |pmid=13816753 |s2cid=11923119 }}</ref> 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.<ref>{{cite journal |vauthors=Peschier |date=1798 |title=Extraits des expériences de Jurine sur les chauve-souris qu'on a privé de la vue |trans-title=Extracts of Jurine's experiments on bats that have been deprived of sight |language=fr |journal=Journal de physique, de chimie, d'histoire naturelle |volume=46 |pages=145–148 |url=https://babel.hathitrust.org/cgi/pt?id=pst.000025234138;view=1up;seq=150}}</ref><ref>{{cite journal |title=Experiments on bats deprived of sight |journal=[[Philosophical Magazine]] |volume=1 |issue=2 |pages=136–140 |quote= From p. 140: From these experiments the author concludes: … that the organ of hearing appears to supply that of sight in the discovery of bodies, and to furnish these animals with different sensations to direct their flight, and enable them to avoid those obstacles which may present themselves. |doi=10.1080/14786447808676811 |year=1798 |last1=De Jurine |first1=M. |url=https://zenodo.org/record/1658068 }}</ref><ref>{{cite journal |last1=Dijkgraaf |first1=Sven |year=1949 |title=Spallanzani und die Fledermäuse |trans-title=Spallanzani and the bat |journal=Experientia |volume=5 |issue=2 | pages=90–92 |doi=10.1007/bf02153744 | s2cid=500691 }}</ref> In 1908, Walter Louis Hahn confirmed Spallanzani's and Jurine's findings.<ref>{{cite journal |last=Hahn |first=Walter Louis |date=1908 |url=https://babel.hathitrust.org/cgi/pt?id=hvd.32044106183585;view=1up;seq=159 |title=Some habits and sensory adaptations of cave-inhabiting bats |journal=Biological Bulletin | volume= 15 |issue=3 |pages=135–198; especially pp. 165–178 |doi=10.2307/1536066 |jstor=1536066 |hdl=2027/hvd.32044107327314 |doi-access=free |hdl-access=free }}</ref>

In 1912, the inventor [[Hiram Maxim]] independently proposed that bats used [[Infrasound |sound below the human auditory range]] to avoid obstacles.<ref>{{cite journal |last=Maxim |first=Hiram |date=7 September 1912 |url= https://babel.hathitrust.org/cgi/pt?id=mdp.39015012343854;view=1up;seq=152 |title=The sixth sense of the bat. Sir Hiram Maxim's contention. The possible prevention of sea collisions. |journal=Scientific American Supplement |volume=74 |pages=148–150 }}</ref> In 1920, the English physiologist [[Hamilton Hartridge]] correctly proposed instead that bats used [[ultrasound|frequencies above the range of human hearing]].<ref>{{cite journal |last=Hartridge |first=H. |date=1920 |url=https://babel.hathitrust.org/cgi/pt?id=inu.30000088598481;view=1up;seq=72 |title=The avoidance of objects by bats in their flight |journal=Journal of Physiology |volume=54 |issue=1–2 |pages=54–57 |doi=10.1113/jphysiol.1920.sp001908 |pmid=16993475 |pmc=1405739 }}</ref><ref>{{cite journal |last=<!--Thorpe?--> |date=1958 |title=Review of 'Listening in the Dark' |journal=Science |volume=128 |issue=3327 |page=766 |jstor=1754799 |doi=10.1126/science.128.3327.766 }}</ref>

Echolocation in [[odontocetes]] (toothed whales) was not properly described until two decades after Griffin and Galambos' work, by [[William E. Schevill |Schevill]] and McBride in 1956.<ref>{{cite journal |last1=Schevill |first1=W. E. |last2=McBride |first2=A. F. |year=1956 |title=Evidence for echolocation by cetaceans |journal=Deep-Sea Research |volume=3 |issue=2 | pages=153–154 |doi=10.1016/0146-6313(56)90096-x |bibcode=1956DSR.....3..153S }}</ref> However, in 1953, [[Jacques Yves Cousteau]] suggested in his first book, ''[[The Silent World: A Story of Undersea Discovery and Adventure |The Silent World]]'', that porpoises had something like [[sonar]], judging by their navigational abilities.<ref>{{cite book |last=Cousteau |first=Jacques Yves |author-link=Jacques Yves Cousteau |title-link=The Silent World: A Story of Undersea Discovery and Adventure |title=The Silent World |date=1953 |publisher=Harper and Brothers |pages=206–207}}</ref>

== Principles ==

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.<ref>{{cite journal |last=Jones |first=G. |title=Echolocation |journal=Current Biology |volume=15 |issue=13 |pages=R484–R488 |date=July 2005 |pmid=16005275 |doi=10.1016/j.cub.2005.06.051 |s2cid=235311777 |doi-access=free |bibcode=2005CBio...15.R484J }}</ref>

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.<ref>{{cite journal |last1=Lewanzik |first1=Daniel |last2=Sundaramurthy |first2=Arun K. |last3=Goerlitz |first3=Holger |title=Insectivorous bats integrate social information about species identity, conspecific activity and prey abundance to estimate cost-benefit ratio of interactions |journal=The Journal of Animal Ecology |volume=88 |issue=10 |pages=1462–1473 |date=October 2019 |pmid=30945281 |pmc=6849779 |doi=10.1111/1365-2656.12989 |bibcode=2019JAnEc..88.1462L |editor-first=Elizabeth |editor-last=Derryberry }}</ref><ref>{{cite journal |last1=Shriram |first1=Uday |last2=Simmons |first2=James A. | title=Echolocating bats perceive natural-size targets as a unitary class using micro-spectral ripples in echoes |journal=Behavioral Neuroscience |volume=133 |issue=3 |pages=297–304 |date=June 2019 |pmid=31021108 |doi=10.1037/bne0000315 |doi-access=free }}</ref>

=== Acoustic features ===

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.<ref name="Thaler Goodale 2016">{{cite journal | last1=Thaler | first1=Lore | last2=Goodale | first2=Melvyn A. | title=Echolocation in humans: an overview | journal=WIREs Cognitive Science | publisher=Wiley | volume=7 | issue=6 | date=19 August 2016 | issn=1939-5078 | doi=10.1002/wcs.1408 | pages=382–393 | pmid=27538733 | url=https://dro.dur.ac.uk/19632/1/19632.pdf |quote=Bats and dolphins are known for their ability to use echolocation. ... some blind people have learned to do the same thing ... }}</ref><!--<ref name="Jones_2006"/><ref name="Simmons_1980"/>--><ref name="Hiryu_2007">{{cite journal |last1=Hiryu |first1=Shizuko |last2=Hagino |first2=Tomotaka |last3=Riquimaroux |first3=Hiroshi |last4=Watanabe |first4=Yoshiaki |s2cid=14511456 |title=Echo-intensity compensation in echolocating bats (Pipistrellus abramus) during flight measured by a telemetry microphone |journal=The Journal of the Acoustical Society of America |volume=121 |issue=3 |pages=1749–1757 |date=March 2007 |pmid=17407911 |doi=10.1121/1.2431337 |bibcode=2007ASAJ..121.1749H }}</ref>

Bat call frequencies range from as low as 11&nbsp;kHz to as high as 212&nbsp;kHz.<ref name="Jones, G. 2007">{{cite journal |last1=Jones |first1=G. |last2=Holderied |first2=M. W. |title=Bat echolocation calls: adaptation and convergent evolution |journal=Proceedings. Biological Sciences |volume=274 |issue=1612 |pages=905–912 |date=April 2007 |pmid=17251105 |pmc=1919403 |doi=10.1098/rspb.2006.0200 }}</ref> [[Insectivore|Insectivorous]] aerial-hawking bats, those that chase prey in the open air, have a call [[frequency]] between 20&nbsp;kHz and 60&nbsp;kHz, because it is the frequency that gives the best range and image acuity and makes them less conspicuous to insects.<ref>{{cite journal |last1=Fenton |first1=M. B. |last2=Portfors |first2=C. V. |last3=Rautenbach |first3=I. L. |last4=Waterman |first4=J. M. |year=1998 |title=Compromises: Sound frequencies used in echolocation by aerial-feeding bats | journal=Canadian Journal of Zoology |volume=76 |issue=6 | pages=1174–1182 |doi=10.1139/cjz-76-6-1174}}</ref> However, low frequencies are adaptive for some species with different prey and environments. ''[[Euderma maculatum]]'', a bat species that feeds on [[moth]]s, uses a particularly low frequency of 12.7&nbsp;kHz that cannot be heard by moths.<ref name="Fullard_1997">{{cite journal |last1=Fullard |first1=J. |last2=Dawson |first2=J. |title=The echolocation calls of the spotted bat Euderma maculatum are relatively inaudible to moths |journal=The Journal of Experimental Biology |volume=200 |issue=Pt 1 |pages=129–137 |year=1997 |doi=10.1242/jeb.200.1.129 |pmid=9317482 }}</ref>

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.<ref>{{Cite journal |last1=Fenton |first1=M. Brock |last2=Faure |first2=Paul A. |last3=Ratcliffe |first3=John M. |date=1 September 2012 |title=Evolution of high duty cycle echolocation in bats |url=https://journals.biologists.com/jeb/article/215/17/2935/10996/Evolution-of-high-duty-cycle-echolocation-in-bats |journal=Journal of Experimental Biology |volume=215 |issue=17 |pages=2935–2944 |doi=10.1242/jeb.073171 |pmid=22875762 |s2cid=405317 |issn=1477-9145|doi-access=free |url-access=subscription }}</ref>

Echolocation calls in bats have been measured at intensities anywhere between 60 and 140 [[decibels]].<ref>{{cite journal |last1=Surlykke |first1=A. |last2=Kalko |first2=E. K. |title=Echolocating bats cry out loud to detect their prey |journal=PLOS ONE |volume=3 |issue=4 |pages=e2036 |date=April 2008 |pmid=18446226 |pmc=2323577 |doi=10.1371/journal.pone.0002036 |bibcode=2008PLoSO...3.2036S |doi-access=free }}</ref> 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.<ref name="Hiryu_2007"/> High-intensity calls such as those from aerial-hawking bats (133&nbsp;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.<ref>{{cite journal |last1=Holderied |first1=M. W. |last2=von Helversen |first2=O. |title=Echolocation range and wingbeat period match in aerial-hawking bats |journal=Proceedings. Biological Sciences |volume=270 |issue=1530 |pages=2293–2299 |date=November 2003 |pmid=14613617 |pmc=1691500 |doi=10.1098/rspb.2003.2487 }}</ref> 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.<ref name="Fullard_1997"/><ref name="Brinklov">{{cite journal |last1=Brinklov |first1=S. |last2=Kalko |first2=E. K. V. |last3=Surlykke |first3=A. |title=Intense echolocation calls from two 'whispering' bats, Artibeus jamaicensis and Macrophyllum macrophyllum (Phyllostomidae) |journal=Journal of Experimental Biology |date=16 December 2008 |volume=212 |issue=1 |pages=11–20 |doi=10.1242/jeb.023226 |pmid=19088206 |doi-access=free}}</ref>

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.<ref name="Jones 1999">{{cite journal |last1=Jones |first1=Gareth |title=Scaling of Echolocation Call Parameters in Bats |journal=Journal of Experimental Biology |date=1999 |volume=202 |issue=23 |pages=3359–3367 |doi=10.1242/jeb.202.23.3359 |pmid=10562518 |url=https://www.researchgate.net/publication/12737724}}</ref>
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.<ref name="Jones, G. 2007"/>

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&nbsp;cm away. Therefore, the bat constantly has to make a choice between getting new information updated quickly and detecting objects far away.<ref>{{cite book |last1=Wilson |first1=W. |last2=Moss |first2=Cynthia |date=2004 |title=Echolocation in Bats and Dolphins |editor1=Thomas, Jeanette |editor2=Moss, Cynthia |editor3=Vater, Marianne |page=22 |publisher=University of Chicago Press |isbn=978-0-2267-9598-0 }}</ref>

=== Tradeoff between FM and CF ===

==== FM signal advantages ====

[[File:Yannick Dauby - Bats echolocation (CC by).ogg|thumb|Echolocation call produced by ''[[Pipistrellus pipistrellus]]'', an FM bat. The ultrasonic call has been "[[heterodyne]]d" – 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 [[sound localization |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.<ref name="Jones_2006"/><ref name="Grinnell 1995"/><ref name="Simmons_1980"/>

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.<ref name="Fenton_1995"/> 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.<ref name="Grinnell 1995"/>

==== CF signal advantages ====

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.<!--<ref name="Simmons_1980"/><ref name="Grinnell 1995"/>--><ref name="Neuweiler_2003">{{cite journal |last=Neuweiler |first=G. |year=2003 |title=Evolutionary aspects of bat echolocation | journal=Journal of Comparative Physiology A |volume=189 |issue=4 | pages=245–256 |doi=10.1007/s00359-003-0406-2 |pmid=12743729 |s2cid=8761216 }}</ref><ref name="Jones_2006"/> The horseshoe bats hunt in this way.<ref name="Schnitzler Flieger 1983">{{cite journal |last1=Schnitzler |first1=H. U. |last2=Flieger |first2=E. |year=1983 |title=Detection of oscillating target movements by echolocation in the Greater Horseshoe bat | journal=Journal of Comparative Physiology |volume=153 |issue=3 | pages=385–391 |doi=10.1007/bf00612592 | s2cid=36824634 }}</ref>

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.<ref name="Grinnell 1995">{{cite book |last=Grinnell |first=A. D. |date=1995 |chapter=Hearing in Bats: An Overview. |title=Hearing in Bats |editor1=Popper, A. N. |editor2=Fay, R. R. |publisher=Springer Verlag |location=New York |pages=1–36 }}</ref><ref name="Fenton_1995"/>

==== Acoustic environments of FM and CF signals ====

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".<ref name="Simmons_1980"/> 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.<!--<ref name="Fenton_1995"/>--><ref name="Neuweiler_2003"/><ref name="Jones_2006"/>

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.<ref name="Neuweiler_2003"/><ref name="Simmons_1980"/><ref name="Jones_2006"/><!--<ref name="Fenton_1995"/>-->

== Taxonomic range ==

Echolocation occurs in a variety of mammals and birds as described below.<ref>{{cite journal |last=Fenton |first=M. Brock |title=Echolocation: Implications for Ecology and Evolution of Bats |journal=The Quarterly Review of Biology |volume=59 |issue=1 |year=1984 |pages=33–53 |doi=10.1086/413674 |jstor=2827869|s2cid=83946162 }}</ref> It evolved repeatedly, an example of [[convergent evolution]].<ref name="Jones_2006"/><ref name="Racicot 2019"/>

{{clade
|label1=[[Tetrapoda]]
|1={{clade
   |label1=[[Mammal]]s 
   |1={{clade
      |label1=[[Boreoeutheria]]
      |1={{clade
         |1={{clade
            |label1=[[Rodent]]ia
            |1='''[[Chinese pygmy dormouse|Chinese pygmy dormice]]'''
            }}
         |label2=Laurasiatheria
         |2={{clade
            |label1=[[Scrotifera]]
            |1={{clade
               |1='''[[Bat]]s'''
               |2='''[[Cetacea|Whales]]'''
               }}
            |label2=[[Eulipotyphla]]
            |2={{clade
               |1='''[[Shrew]]s'''
               |2='''[[Solenodon]]s'''
               }}
            }}
         }}
      |label2=[[Afrotheria]]
      |2={{clade
         |1='''[[Tenrec]]s'''
         }}
      }}
   |label2=[[Bird]]s 
   |2={{clade
      |1='''[[Oilbird]]s'''
      |2='''[[Swiftlet]]s'''
      }}
   }}
}}

=== Bats ===

[[File:Chirps190918-22s2.png|right|thumb|upright=1.5|[[Spectrogram]] of ''[[Pipistrellus pipistrellus]]'' bat vocalizations during prey approach. The recording covers a total of 1.1&nbsp;seconds; lower main frequency c. 45&nbsp;kHz (as typical for a common pipistrelle). About 150&nbsp;milliseconds before final contact time between and duration of calls are becoming much shorter ("feeding buzz").<br/>Corresponding audio file: [[File:Chirps190918-22s.mp3 |Audio recording: Common pipistrelle approaching prey, 20 fold dilated]] ]]

{{Listen |filename=Pipistrellus.ogg |title=Pipistrellus calls |description=Recording of ''Pipistrellus''; echolocation call followed by a social call. |format=[[Ogg]]}}

Echolocating bats use echolocation to [[Animal navigation |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 [[insect]]s (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.<ref>{{cite journal |last1=Lima |first1=Steven L. |last2=O'Keefe |first2=Joy |title=Do predators influence the behaviour of bats? |journal=Biological Reviews of the Cambridge Philosophical Society |volume=88 |issue=3 |pages=626–644 |date=August 2013 |pmid=23347323 |doi=10.1111/brv.12021 |s2cid=32118961 |doi-access=free }}</ref>

Echolocating bats generate [[ultrasound]] via the [[larynx]] and emit the sound through the open mouth or, much more rarely, the nose.<ref>{{cite journal |last1=Teeling |first1=E. C. |last2=Madsen|first2=O. |last3=Van Den Bussche |first3=R. A. |last4=de Jong |first4=W. W. |last5=Stanhope |first5=M. J. |last6=Springer |first6=M. S. |year=2002 |title=Microbat paraphyly and the convergent evolution of a key innovation in Old World rhinolophoid microbats |journal=PNAS |volume=99 |issue=3 |pages=1431–1436 |doi=10.1073/pnas.022477199 |pmid=11805285 |pmc=122208 |bibcode=2002PNAS...99.1431T |doi-access=free}}</ref> 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&nbsp;Hz, mostly beyond the range of the human ear (typical human hearing range is considered to be from 20&nbsp;Hz to 20,000&nbsp;Hz). Bats may estimate the elevation of targets by interpreting the [[interference pattern]]s caused by the echoes reflecting from the [[tragus (ear) |tragus]], a flap of skin in the external ear.<ref>{{cite journal |last=Müller |first=R. |title=A numerical study of the role of the tragus in the big brown bat |journal=The Journal of the Acoustical Society of America |volume=116 |issue=6 |pages=3701–3712 |date=December 2004 |pmid=15658720 |doi=10.1121/1.1815133 |bibcode=2004ASAJ..116.3701M }}</ref>

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.<ref>{{cite web |title=Wyoming Bat Call Library |url=http://www.uwyo.edu/wyndd/data-dissemination/priority-data-comp/wyoming-bat-call-library/index.html |website=University of Wyoming |access-date=16 January 2019 |archive-date=16 January 2019 |archive-url=https://web.archive.org/web/20190116100142/http://www.uwyo.edu/wyndd/data-dissemination/priority-data-comp/wyoming-bat-call-library/index.html |url-status=dead }}</ref><ref>{{cite web |title=Pacific Northwest Bat Call Library |url=http://depts.washington.edu/sdwasm/pnwbat/batcall.html |website=University of Washington |access-date=16 January 2019}}</ref><ref>{{cite journal |last1=Fukui |first1=Dai |last2=Agetsuma |first2=Naoki |last3=Hill |first3=David A. |title=Acoustic identification of eight species of bat (mammalia: chiroptera) inhabiting forests of southern hokkaido, Japan: potential for conservation monitoring |journal=Zoological Science |volume=21 |issue=9 |pages=947–955 |date=September 2004 |pmid=15459453 |doi=10.2108/zsj.21.947 |url=https://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/14484/1/ZS_21_947.pdf |hdl=2115/14484 |s2cid=20190217 }}</ref>

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.<ref>{{cite journal |last1=Speakman |first1=J. R. |last2=Racey |first2=P. A. |title=No cost of echolocation for bats in flight |journal=Nature |volume=350 |issue=6317 |pages=421–423 |date=April 1991 |pmid=2011191 |doi=10.1038/350421a0 |bibcode=1991Natur.350..421S |s2cid=4314715 }}</ref> 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.<ref>{{cite journal |last1=Gordon |first1=Shira D. |last2=ter Hofstede |first2=Hannah M. |title=The influence of bat echolocation call duration and timing on auditory encoding of predator distance in noctuoid moths |journal=The Journal of Experimental Biology |volume=221 |issue=Pt 6 |page=jeb171561 |date=March 2018 |pmid=29567831 |doi=10.1242/jeb.171561 |doi-access=free }}</ref>

==== Bat evolution ====

Bats evolved at the start of the [[Eocene]] epoch, around 64 [[myr|mya]]. The Yangochiroptera appeared some 55 mya, and the Rhinolophoidea some 52 mya.<ref name="Teeling Springer Madsen Bates 2005">{{cite journal | last1=Teeling | first1=Emma C. | last2=Springer | first2=Mark S. | last3=Madsen | first3=Ole | last4=Bates | first4=Paul | last5=O'Brien | first5=Stephen J. | last6=Murphy | first6=William J. | title=A Molecular Phylogeny for Bats Illuminates Biogeography and the Fossil Record | journal=Science | publisher=American Association for the Advancement of Science (AAAS) | volume=307 | issue=5709 | date=28 January 2005 | issn=0036-8075 | doi=10.1126/science.1105113 | pages=580–584 | pmid=15681385 | bibcode=2005Sci...307..580T | s2cid=25912333 |url=https://www.researchgate.net/profile/Mark-Springer/publication/8051516_A_Molecular_Phylogeny_for_Bats_Illuminates_Biogeography_and_the_Fossil_Record/links/00b4951800240564a6000000/A-Molecular-Phylogeny-for-Bats-Illuminates-Biogeography-and-the-Fossil-Record.pdf <!--author's website-->}}</ref>

There are two hypotheses about the evolution of echolocation in bats. The first suggests that [[Larynx |laryngeal]] echolocation evolved twice, or more, in Chiroptera, at least once in the [[Yangochiroptera]] and at least once in the horseshoe bats (Rhinolophidae):<ref>{{cite journal |last1=Teeling |first1=Emma C. |last2=Scally |first2=Mark |last3=Kao |first3=Diana J. |last4=Romagnoli |first4=Michael L. |last5=Springer |first5=Mark S. |last6=Stanhope |first6=Michael J. |title=Molecular evidence regarding the origin of echolocation and flight in bats |journal=Nature |volume=403 |issue=6766 |pages=188–192 |date=January 2000 |pmid=10646602 |doi=10.1038/35003188 |bibcode=2000Natur.403..188T |s2cid=205004782 }}; {{cite web | title=Order Chiroptera (Bats) | publisher=Animal Diversity Web |url= http://animaldiversity.ummz.umich.edu/site/accounts/information/Chiroptera.html |access-date =2007-12-30 | archive-url= https://web.archive.org/web/20071221224447/http://animaldiversity.ummz.umich.edu/site/accounts/information/Chiroptera.html |archive-date= 21 December 2007 }}; {{Cite journal |last1=Nojiri |first1=Taro |last2=Wilson |first2=Laura A. B. |last3=López-Aguirre |first3=Camilo |last4=Tu |first4=Vuong Tan |last5=Kuratani |first5=Shigeru |last6=Ito |first6=Kai |last7=Higashiyama |first7=Hiroki |last8=Son |first8=Nguyen Truong |last9=Fukui |first9=Dai |last10=Sadier |first10=Alexa |last11=Sears |first11=Karen E. |display-authors=3 |date=2021-04-12 |title=Embryonic evidence uncovers convergent origins of laryngeal echolocation in bats |journal=Current Biology |volume=31 |issue=7 |pages=1353–1365.e3 |doi=10.1016/j.cub.2020.12.043 |issn=0960-9822 |pmid=33675700 |s2cid=232125726 |doi-access=free|bibcode=2021CBio...31E1353N |hdl=1885/286428 |hdl-access=free }}</ref> 

{{clade
|label1=[[Chiroptera]]
|1={{clade
   |1={{clade
      |1=[[Yangochiroptera]] 
      |sublabel1=''''' CF ''' (Early [[Eocene]])''
      |2={{clade
         |label1=<!--[[Yinpterochiroptera]]-->
         |1={{clade
            |label1=[[Pteropodidae]] 
            |1={{clade
               |1={{clade
                  |1=fruit bats
                  |2='''''[[Rousettus]]'''''
                  |sublabel2='''''tongue-clicking'''''
                  }}
               }}
            |label2=[[Rhinolophoidea]]
            |sublabel2=''''' FM ''' (Early [[Eocene]])''
            |2={{clade
               |1=[[Megadermatidae]] 
               |2=horseshoe bats
               }}
            }}
         }}
      }}
   }}
}}

The second proposes that laryngeal echolocation had a single origin in Chiroptera, i.e. that it was [[Basal (phylogenetics)|basal]] to the group, and was subsequently lost in the family [[Pteropodidae]].<ref name="Jebb Huang Pippel 2020">{{Cite journal |last1=Jebb |first1=David |last2=Huang |first2=Zixia |last3=Pippel |first3=Martin |last4=Hughes |first4=Graham M. |last5=Lavrichenko |first5=Ksenia |last6=Devanna |first6=Paolo |last7=Winkler |first7=Sylke |last8=Jermiin |first8=Lars S. |last9=Skirmuntt |first9=Emilia C. |last10=Katzourakis |first10=Aris |last11=Burkitt-Gray |first11=Lucy |display-authors=3 |date=July 2020 |title=Six reference-quality genomes reveal evolution of bat adaptations |journal=Nature |volume=583 |issue=7817 |pages=578–584 |doi=10.1038/s41586-020-2486-3 |issn=1476-4687 |pmc=8075899 |pmid=32699395 |bibcode=2020Natur.583..578J}}; {{Cite journal |last1=Wang |first1=Zhe |last2=Zhu |first2=Tengteng |last3=Xue |first3=Huiling |last4=Fang |first4=Na |last5=Zhang |first5=Junpeng |last6=Zhang |first6=Libiao |last7=Pang |first7=Jian |last8=Teeling |first8=Emma C. |last9=Zhang |first9=Shuyi |display-authors=3 |date=2017-01-09 |title=Prenatal development supports a single origin of laryngeal echolocation in bats |url=https://www.nature.com/articles/s41559-016-0021 |journal=Nature Ecology & Evolution |volume=1 |issue=2 |page=21 |doi=10.1038/s41559-016-0021 |pmid=28812602 |bibcode=2017NatEE...1...21W |s2cid=29068452 |issn=2397-334X|url-access=subscription }}; {{Cite journal |last1=Thiagavel |first1=Jeneni |last2=Cechetto |first2=Clément |last3=Santana |first3=Sharlene E. |last4=Jakobsen |first4=Lasse |last5=Warrant |first5=Eric J. |last6=Ratcliffe |first6=John M. |display-authors=3 |date=December 2018 |title=Auditory opportunity and visual constraint enabled the evolution of echolocation in bats |journal=Nature Communications |volume=9 |issue=1 |page=98 |doi=10.1038/s41467-017-02532-x |issn=2041-1723 |pmc=5758785 |pmid=29311648 |bibcode=2018NatCo...9...98T }}; {{Cite journal |last=Teeling |first=Emma C. |date=July 2009 |title=Hear, hear: the convergent evolution of echolocation in bats? |url=https://linkinghub.elsevier.com/retrieve/pii/S0169534709001487 |journal=Trends in Ecology & Evolution |volume=24 |issue=7 |pages=351–354 |doi=10.1016/j.tree.2009.02.012 |pmid=19482373 |bibcode=2009TEcoE..24..351T |url-access=subscription }}</ref> Later, the genus ''[[Rousettus]]'' in the Pteropodidae family evolved a different mechanism of echolocation using a system of tongue-clicking:<ref name="Springer Teeling Madsen 2001">{{cite journal |last1=Springer |first1=Mark S. |last2=Teeling |first2=Emma C. |last3=Madsen |first3=Ole |last4=Stanhope |first4=Michael J. |last5=de Jong |first5=Wilfried W. |display-authors=3 |title=Integrated fossil and molecular data reconstruct bat echolocation |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=98 |issue=11 |pages=6241–6246 |date=May 2001 |pmid=11353869 |pmc=33452 |doi=10.1073/pnas.111551998 |bibcode=2001PNAS...98.6241S |doi-access=free }}</ref>

{{clade
|label1=[[Chiroptera]]
|sublabel1=''''' CF ''' (Earliest [[Eocene]])''
|1={{clade
   |1={{clade
      |1=[[Yangochiroptera]] 
      |2={{clade
         |label1=<!--[[Yinpterochiroptera]]-->
         |1={{clade
            |label1=[[Pteropodidae]] 
            |sublabel1='''''CF lost'''''
            |1={{clade
               |1={{clade
                  |1=fruit bats
                  |2='''''[[Rousettus]]'''''
                  |sublabel2='''''tongue-clicking'''''
                  }}
               }}
            |label2=[[Rhinolophoidea]]
            |sublabel2=''''' FM ''' (Early [[Eocene]])''
            |2={{clade
               |1=[[Megadermatidae]] 
               |2=horseshoe bats
               }}
            }}
         }}
      }}
   }}
}}

==== Calls and ecology ====

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.<ref name="Jones_2006">{{cite journal |last1=Jones |first1=G. |last2=Teeling |first2=E. |title=The evolution of echolocation in bats |journal=Trends in Ecology & Evolution |volume=21 |issue=3 |pages=149–156 |date=March 2006 |pmid=16701491 |doi=10.1016/j.tree.2006.01.001 }}</ref><!--<ref name="Grinnell 1995"/>--><!--<ref name="Zupanc 2004">{{cite book |last=Zupanc |first=Günther K. H. |date=2004 |title=Behavioral Neurobiology: An Integrative Approach |publisher=Oxford University Press |location=Oxford, UK |isbn=978-0-1987-3872-5 |pages= }}</ref>--><ref name="Fenton_1995">{{cite book |last=Fenton |first=M. B. |date=1995 |chapter=Natural History and Biosonar Signals |title=Hearing in Bats |editor1=Popper, A. N. |editor2=Fay, R. R. |publisher=Springer Verlag |location=New York |pages=37–86}}</ref><!--<ref name="Neuweiler_2003"/>--><ref name="Simmons_1980">{{cite journal |last1=Simmons |first1=J. A. |last2=Stein |first2=R. A. |year=1980 |title=Acoustic Imaging in bat sonar: echolocation signals and the evolution of echolocation | journal=Journal of Comparative Physiology A |volume=135 |issue=1 |pages=61–84 |doi=10.1007/bf00660182 |s2cid=20515827 }}</ref> Bats can inadvertently jam each other, and in some situations they may stop calling to avoid jamming.<ref name="Chiu Xian 2008">{{cite journal |last1=Chiu |first1=Chen |last2=Xian |first2=Wei |last3=Moss |first3=Cynthia F. |title=Flying in silence: Echolocating bats cease vocalizing to avoid sonar jamming |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=105 |issue=35 |pages=13116–21 |date=September 2008 |pmid=18725624 |pmc=2529029 |doi=10.1073/pnas.0804408105 |bibcode=2008PNAS..10513116C |doi-access=free }}</ref>

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 [[Tympanal organ|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.<ref>{{Cite journal |last1=Kawahara |first1=Akito Y. |last2=Plotkin |first2=David |last3=Espeland |first3=Marianne |last4=Meusemann |first4=Karen |last5=Toussaint |first5=Emmanuel F. A. |last6=Donath |first6=Alexander |last7=Gimnich |first7=France |last8=Frandsen |first8=Paul B. |last9=Zwick |first9=Andreas |last10=dos Reis |first10=Mario |last11=Barber |first11=Jesse R. |last12=Peters |first12=Ralph S. |last13=Liu |first13=Shanlin |last14=Zhou |first14=Xin |last15=Mayer |first15=Christoph |date=2019-11-05 |title=Phylogenomics reveals the evolutionary timing and pattern of butterflies and moths |journal=Proceedings of the National Academy of Sciences |language=en |volume=116 |issue=45 |pages=22657–22663 |doi=10.1073/pnas.1907847116 |doi-access=free |issn=0027-8424 |pmc=6842621 |pmid=31636187|bibcode=2019PNAS..11622657K }}</ref> These moth adaptations provide [[Evolutionary pressure |selective pressure]] for bats to improve their insect-hunting systems and this cycle culminates in a moth-bat "[[evolutionary arms race]]".<ref>{{cite journal |last1=Goerlitz |first1=Holger R. |last2=ter Hofstede |first2=Hannah M. |last3=Zeale |first3=Matt R. K. |last4=Jones |first4=Gareth |last5=Holderied |first5=Marc W. |title=An aerial-hawking bat uses stealth echolocation to counter moth hearing |journal=Current Biology |volume=20 |issue=17 |pages=1568–1572 |date=September 2010 |pmid=20727755 |doi=10.1016/j.cub.2010.07.046 |doi-access=free |bibcode=2010CBio...20.1568G }}</ref><ref>{{cite journal |last1=Ratcliffe |first1=John M. |last2=Elemans |first2=Coen P. H. |last3=Jakobsen |first3=Lasse |last4=Surlykke |first4=Annemarie |title=How the bat got its buzz |journal=Biology Letters |volume=9 |issue=2 |pages=20121031 |date=April 2013 |pmid=23302868 |pmc=3639754 |doi=10.1098/rsbl.2012.1031 }}</ref>

==== Neural mechanisms ====

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.<ref>{{cite journal |last1=Salles |first1=Angeles |last2=Bohn |first2=Kirsten M. |last3=Moss |first3=Cynthia F. |s2cid=143423009 |title=Auditory communication processing in bats: What we know and where to go |journal=Behavioral Neuroscience |volume=133 |issue=3 |pages=305–319 |date=June 2019 |pmid=31045392 |doi=10.1037/bne0000308 |doi-access=free }}</ref>

===== Inner ear and primary sensory neurons =====

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.<ref name="Neuweiler_2003"/>

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&nbsp;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]]".<ref>{{cite journal |last1=Schuller |first1=G. |last2=Pollack |first2=G. |year=1979 |title=Disproportionate frequency representation in the inferior colliculus of Doppler-compensating greater horseshoe bats: Evidence of an acoustic fovea | journal=Journal of Comparative Physiology A |volume=132 |issue=1 | pages=47–54 |doi=10.1007/bf00617731 | s2cid=7176515 |url=https://epub.ub.uni-muenchen.de/3159/ |url-access=subscription }}
</ref>

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.<ref>{{Cite journal |last1=Liu |first1=Zhen |last2=Chen |first2=Peng |last3=Li |first3=Yuan-Yuan |last4=Li |first4=Meng-Wen |last5=Liu |first5=Qi |last6=Pan |first6=Wen-Lu |last7=Xu |first7=Dong-Ming |last8=Bai |first8=Jing |last9=Zhang |first9=Li-Biao |last10=Tang |first10=Jie |last11=Shi |first11=Peng |display-authors=3 |date=November 2021 |title=Cochlear hair cells of echolocating bats are immune to intense noise |url=https://linkinghub.elsevier.com/retrieve/pii/S1673852721001910 |journal=Journal of Genetics and Genomics |volume=48 |issue=11 |pages=984–993 |doi=10.1016/j.jgg.2021.06.007 |pmid=34393089 |s2cid=237094069 |url-access=subscription }}</ref> 

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.<ref name="Carew_2001">{{cite book |last=Carew |first=T. |date=2004 |orig-year=2001 |title=Behavioral Neurobiology: The Cellular Organization of Natural Behavior |publisher=Oxford University Press |isbn=978-0-8789-3084-5 |chapter=<!--Part II: Sensory Worlds: -->Echolocation in Bats}}</ref>

===== Inferior colliculus =====

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.<ref name="Pollak Marsh 1977"/> These interneurons are specialized for time sensitivity in several ways. First, when activated, they generally respond with only one or two [[action potential]]s. 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.<!--<ref name="Carew_2001"/>--><ref name="Pollak Marsh 1977">{{cite journal |last1=Pollak |first1=George |last2=Marsh |first2=David |last3=Bodenhamer |first3=Robert |last4=Souther |first4=Arthur |title=Echo-detecting characteristics of neurons in inferior colliculus of unanesthetized bats |journal=Science |volume=196 |issue=4290 |pages=675–678 |date=May 1977 |pmid=857318 |doi=10.1126/science.857318 |bibcode=1977Sci...196..675P }}</ref>

===== Auditory cortex =====

The [[auditory cortex]] in bats is quite large in comparison with other mammals.<ref>{{cite journal |last1=Kanwal |first1=Jagmeet S. |last2=Rauschecker |first2=J. P. |title=Auditory cortex of bats and primates: managing species-specific calls for social communication |journal=Frontiers in Bioscience |volume=12 |issue=8–12 |pages=4621–4640 |date=May 2007 |pmid=17485400 |pmc=4276140 |doi=10.2741/2413 }}</ref> 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.<ref name="Suga 1975"/><ref name="Suga 1987"/>

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.<ref name="Suga 1975"/><ref name="Suga 1987"/>

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:<ref name="Suga 1975"/><ref name="Suga 1987"/>

[[File:Bat Auditory Cortex.svg|thumb|upright=1.2|Auditory cortex of a bat
{{legend |#BA54C0 |FM-FM area |text=A |textcolor=white}}
{{legend |#4190B9 |CF-CF area |text=B |textcolor=white}}
{{legend |#4AB8B6 |Amplitude-sensitive area |text=C |textcolor=white}}
{{legend |#DC7A5B |Frequency-sensitive area |text=D |textcolor=white}}
{{legend |#90C675 |DSCF area |text=E |textcolor=white}}]]

*'''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.<!--<ref name="Neuweiler_2003"/><ref name="Carew_2001"/>--><ref name="Suga 1975">{{cite journal |last1=Suga |first1=N. |last2=Simmons |first2=J. A. |last3=Jen |first3=P. H. |year=1975 |title=Peripheral specialization for fine analysis of doppler-shifted echoes in the auditory system of the "CF-FM" bat Pteronotus parnellii | journal=Journal of Experimental Biology |volume=63 |issue=1 | pages=161–192 |doi=10.1242/jeb.63.1.161 |pmid=1159359 }}</ref><ref>{{cite journal |last1=Suga |first1=N. |last2=O'Neill |first2=W. E. |s2cid=11840108 |title=Neural axis representing target range in the auditory cortex of the mustache bat |journal=Science |volume=206 |issue=4416 |pages=351–353 |date=October 1979 |pmid=482944 |doi=10.1126/science.482944 |bibcode=1979Sci...206..351S }} </ref>
*'''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&nbsp;kHz (CF1) and one of its additional [[harmonics]] around 60 or 90&nbsp;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<ref name="Carew_2001"/><ref name="Suga 1975"/><ref name="Suga 1987">{{cite journal |last1=Suga |first1=N. |last2=Niwa |first2=H. |last3=Taniguchi |first3=I. |last4=Margoliash |first4=D. |s2cid=18390219 |title=The personalized auditory cortex of the mustached bat: adaptation for echolocation |journal=Journal of Neurophysiology |volume=58 |issue=4 |pages=643–654 |date=October 1987 |pmid=3681389 |doi=10.1152/jn.1987.58.4.643 }}</ref>
*'''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&nbsp;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.<ref name="Carew_2001"/><ref name="Suga 1975"/><ref name="Suga 1987"/>

=== Whales ===

[[File:Toothed whale sound production.svg|thumb|upright=1.8|right |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 [[dolphin]]s, [[porpoise]]s, [[river dolphin]]s, [[killer whale]]s and [[sperm whale]]s, and [[baleen whales]] (suborder [[Mysticeti]]), including [[right whales|right]], [[bowhead whales |bowhead]], [[pygmy right whales |pygmy right]], and [[gray whales]] and [[rorquals]], because they live in an underwater habitat that has favourable acoustic characteristics and where [[visual perception |vision]] is often extremely limited in range due to absorption or [[turbidity]].<ref>{{cite book |last1=Hughes |first1=H. C. |title=Sensory Exotica: A World Beyond Human Experience |date=1999 |publisher=A Bradford Book |location=Cambridge, Massachusetts}}</ref> [[Odontocetes]] are generally able to hear sounds at [[ultrasonic]] frequencies while [[mysticetes]] hear sounds within the [[infrasonic]] frequency regime.<ref name="Viglino 2021">{{cite journal |last1=Viglino |first1=M. |last2=Gaetán |first2=M. |last3=Buono |first3=M. R. |last4=Fordyce |first4=R. E. |last5=Park |first5=T. |title=Hearing from the ocean and into the river: the evolution of the inner ear of Platanistoidea (Cetacea: Odontoceti) |journal=Paleobiology |date=2021 |volume=47 |issue=4 |pages=591–611 |doi=10.1017/pab.2021.11 | bibcode=2021Pbio...47..591V |s2cid=233517623 |url=https://zenodo.org/record/4480277 }}</ref>

==== Whale evolution ====

[[Cetacea]]n evolution consisted of three main [[Evolutionary radiation|radiations]]. Throughout the middle and late [[Eocene]] periods (49-31.5 million years ago), [[archaeocete]]s, primitive toothed Cetacea that arose from terrestrial mammals, were the only cetaceans.<ref name="Gatesy Geisler Chang 2012">{{cite journal |last1=Gatesy |first1=John |last2=Geisler |first2=Jonathan H. |last3=Chang |first3=Joseph |author4=Buell, Carl |author5=Berta, Annalisa |author6=Meredith, Robert W. |author7=Springer, Mark S. |author8=McGowen, Michael R. |display-authors=3 |year=2012 |title=A phylogenetic blueprint for a modern whale |journal=[[Molecular Phylogenetics and Evolution]] |volume=66 |issue=2 |pages=479–506 |doi=10.1016/j.ympev.2012.10.012 |pmid=23103570}}</ref><ref name="Fordyce 1980">{{cite journal |last1=Fordyce |first1=R. E. |year=1980 |title=Whale evolution and oligocene southern-ocean environments | journal= Palaeogeography, Palaeoclimatology, Palaeoecology |volume=31 |pages=319–336 |doi=10.1016/0031-0182(80)90024-3 |bibcode=1980PPP....31..319F |doi-access=free }}</ref> They did not echolocate, but had slightly adapted underwater hearing.<ref name="Fordyce 2003">{{cite book |last=Fordyce |first=R. E. |year=2003 |chapter=Cetacean Evolution and Eocene-Oligocene oceans revisited |editor1=Prothero, Donald R. |editor2=Ivany, Linda C. |editor3=Nesbitt, Elizabeth A. |title=From Greenhouse to Icehouse: the Marine Eocene-Oligocene Transition |publisher=[[Columbia University Press]] |pages=154–170 |isbn=978-0-2311-2716-5}}</ref> By the late middle Eocene, acoustically isolated ear bones had evolved to give [[Basilosauridae|basilosaurid]] archaeocetes directional underwater hearing at low to mid frequencies.<ref name="Lindberg 2007">{{cite journal |last1=Lindberg |first1=D. R. |last2=Pyenson |first2=Nicholas D. |author2-link=Nicholas Pyenson |year=2007 |title=Things that go bump in the night: evolutionary interactions between cephalopods and cetaceans in the tertiary |journal=Lethaia |volume=40 |issue=4 | pages=335–343 |doi=10.1111/j.1502-3931.2007.00032.x|bibcode=2007Letha..40..335L }}</ref> 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.<ref name="Fordyce 1980"/> Extant odontocetes are [[monophyletic]] (a single evolutionary group), but echolocation evolved twice, convergently: once in ''[[Xenorophus]]'', an Oligocene [[Stem-group|stem]] odontocete, and once in the [[crown group|crown]] odontocetes.<ref name="Racicot 2019">{{cite journal |last1=Racicot |first1=Rachel A. |last2=Boessenecker |first2=Robert W. |last3=Darroch |first3=Simon A. F. |last4=Geisler |first4=Jonathan H. |year=2019 |title=Evidence for convergent evolution of ultrasonic hearing in toothed whales |journal=Biology Letters |volume=15 |issue=5 |pages=20190083 |doi=10.1098/rsbl.2019.0083 |pmid=31088283 |s2cid=155091623 |pmc=6548736 }}</ref> 

{{clade
|label1=<!--<ref name="Gatesy Geisler Chang 2012"/>--> 
|1={{clade
   |label1=[[Cetacea]]
   |1={{clade
      |label2='''''directional u/water hearing'''''
      |sublabel2=''mid/late [[Eocene]]''
      |2=[[Basilosauridae]] † 
      |1={{clade
         |label1=[[Odontoceti]] 
         |sublabel1=''[[Oligocene]]''
         |1={{clade
            |label1='''''echolocation'''''
            |sublabel1=''late [[Oligocene]]''
            |1=''[[Xenorophus]]'' † 
            |label2='''''echolocation'''''
            |2={{clade
               |1=[[Physeteroidea]]
               |2={{clade
                  |1=[[Ziphiidae]], etc.
                  |label2=''adaptive radiation''
                  |sublabel2=''[[Miocene]]''
                  |2=[[Delphinoidea]]
                  }}
               }}
            }}
         |label2='''''echolocation'''''
         |sublabel2=''middle [[Oligocene]]''
         |2=[[Mysticeti]]
         }} 
      }} 
   }}
}}

{| style="font-size: 10px; background: whitesmoke; float:right;"
|+ style="font-size:12px;" | '''Cetacean evolution timeline'''<ref name="Fordyce 1980"/>
|- style="background:lightgray;"
! scope="col" style="width: 50px;" | Epoch
! scope="col" style="width: 55px;" | Start date
! scope="col" style="width: 100px;" | Event
|- 
| [[Miocene]] || 23 [[Myr|mya]] || [[Adaptive radiation]], esp. of dolphins
|-
| [[Oligocene]] || 34 mya || [[Odontocetes]] echolocation
|-
| [[Eocene]] || 49 mya || [[Archaeoceti|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 and icehouse Earth|greenhouse to an icehouse world]]. Tectonic openings created the [[Southern Ocean]] with a free flowing [[Antarctic Circumpolar Current]].<!--<ref name="Fordyce 1980"/>--><ref name="Fordyce 2003"/><ref name="Lindberg 2007"/><ref name="Steeman_2009">{{cite journal |last1=Steeman |first1=Mette E. |last2=Hebsgaard |first2=Martin B. |last3=Fordyce |first3=R. Ewan |last4=Ho |first4=Simon Y. W. |last5=Rabosky |first5=Daniel L. |last6=Nielsen |first6=Rasmus |last7=Rahbek |first7=Carsten |last8=Glenner |first8=Henrik |last9=Sørensen |first9=Martin V. |last10=Willerslev |first10=Eske |display-authors=3 |title=Radiation of extant cetaceans driven by restructuring of the oceans |journal=Systematic Biology |volume=58 |issue=6 |pages=573–585 |date=December 2009 |pmid=20525610 |pmc=2777972 |doi=10.1093/sysbio/syp060 }}</ref> 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 vertical migration|diel migrating]] [[cephalopods]].<ref name="Lindberg 2007"/><ref>{{cite journal |last1=Fordyce |first1=R. Ewan |last2=Barnes |first2=Lawrence G. |year=1994 |title=The evolutionary history of whales and dolphins | journal=Annual Review of Earth and Planetary Sciences |volume=22 |issue=1 | pages=419–455 |doi=10.1146/annurev.ea.22.050194.002223 | bibcode=1994AREPS..22..419F }}</ref> The family [[Delphinidae]] (dolphins) diversified in the [[Neogene]] (23–2.6 million years ago), evolving extremely specialized echolocation.<ref>{{cite journal | last1=McGowen |first1=Michael R. |last2=Spaulding |first2=Michelle |last3=Gatesy |first3=John |title=Divergence date estimation and a comprehensive molecular tree of extant cetaceans |journal=Molecular Phylogenetics and Evolution |volume=53 |issue=3 |pages=891–906 |date=December 2009 |pmid=19699809 |doi=10.1016/j.ympev.2009.08.018 }}</ref><ref name="Fordyce 2003"/>

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.<ref name="Liu Rossiter Xiuqun 2010">{{cite journal | last1=Liu |first1=Yang |last2=Rossiter |first2=Stephen J. |last3=Han |first3=Xiuqun |last4=Cotton |first4=James A. |last5=Zhang |first5=Shuyi |title=Cetaceans on a molecular fast track to ultrasonic hearing |journal=Current Biology |volume=20 |issue=20 |pages=1834–1839 |date=October 2010 |pmid=20933423 |doi=10.1016/j.cub.2010.09.008 |doi-access=free |bibcode=2010CBio...20.1834L }}</ref> It has undergone two clear episodes of accelerated evolution in cetaceans.<ref name="Liu Rossiter Xiuqun 2010"/> The first is connected to odontocete divergence, when echolocation first developed, and the second with the increase in echolocation frequency among dolphins. [[TMC1|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.<ref name="Davies Cotton Kirwan 2012">{{Cite journal |last1=Davies |first1=K. T. J. |last2=Cotton |first2=J. A. |last3=Kirwan |first3=J. D. |last4=Teeling |first4=E. C. |last5=Rossiter |first5=S. J. |date=May 2012 |title=Parallel signatures of sequence evolution among hearing genes in echolocating mammals: an emerging model of genetic convergence |journal=Heredity |volume=108 |issue=5 |pages=480–489 |doi=10.1038/hdy.2011.119 |issn=1365-2540 |pmc=3330687 |pmid=22167055}}</ref> [[Molecular evolution]] of Tmc1 and Pjvk indicates positive selection for echolocation in odontocetes.<ref name="Davies Cotton Kirwan 2012"/> [[CLDN14|Cldn14]], a member of the tight junction proteins which form barriers between inner ear cells, shows the same evolutionary pattern as Prestin.<ref>{{cite journal | last1=Xu |first1=Huihui |last2=Liu |first2=Yang |last3=He |first3=Guimei |last4=Rossiter |first4=Stephen J. |last5=Zhang |first5=Shuyi |title=Adaptive evolution of tight junction protein claudin-14 in echolocating whales |journal=Gene |volume=530 |issue=2 |pages=208–214 |date=November 2013 |pmid=23965379 |doi=10.1016/j.gene.2013.08.034 }}</ref> 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.<ref name="Steeman_2009"/>

The evolution of two cranial structures may be linked to echolocation. Cranial telescoping (overlap between [[Frontal bone|frontal]] and [[maxilla]]ry bones, and rearwards displacement of the nostrils<ref name="Roston Roth 2019">{{cite journal | last1=Roston | first1=Rachel A. | last2=Roth | first2=V. Louise | title=Cetacean Skull Telescoping Brings Evolution of Cranial Sutures into Focus | journal=The Anatomical Record | publisher=Wiley | volume=302 | issue=7 | date=8 March 2019 | issn=1932-8486 | doi=10.1002/ar.24079 | pages=1055–1073| pmid=30737886 | pmc=9324554 }}</ref>) developed first in [[Xenorophidae|xenorophids]]. It evolved further in stem odontocetes, arriving at full cranial telescoping in the crown odontocetes.<ref name="Churchill Geisler Beatty 2018">{{Cite journal |last1=Churchill |first1=Morgan |last2=Geisler |first2=Jonathan H. |last3=Beatty |first3=Brian L. |last4=Goswami |first4=Anjali |date=2018 |title=Evolution of cranial telescoping in echolocating whales (Cetacea: Odontoceti) |url=https://onlinelibrary.wiley.com/doi/abs/10.1111/evo.13480 |journal=Evolution |volume=72 |issue=5 |pages=1092–1108 |doi=10.1111/evo.13480 |pmid=29624668 |s2cid=4656605 |issn=1558-5646|url-access=subscription }}</ref> Movement of the nostrils may have allowed for a larger nasal apparatus and [[Melon (cetacean)|melon]] for echolocation.<ref name="Churchill Geisler Beatty 2018"/> This change occurred after the divergence of the neocetes from the basilosaurids.<ref name="Coombs Clavel Park 2020">{{Cite journal |last1=Coombs |first1=Ellen J. |last2=Clavel |first2=Julien |last3=Park |first3=Travis |last4=Churchill |first4=Morgan |last5=Goswami |first5=Anjali |date=2020-07-10 |title=Wonky whales: the evolution of cranial asymmetry in cetaceans |journal=BMC Biology |volume=18 |issue=1 |page=86 |doi=10.1186/s12915-020-00805-4 |issn=1741-7007 |pmc=7350770 |pmid=32646447 |doi-access=free }}</ref> The first shift towards cranial asymmetry occurred in the Early Oligocene, prior to the xenorophids.<ref name="Coombs Clavel Park 2020"/> A xenorophid fossil (''Cotylocara macei'') has cranial asymmetry, and shows other indicators of echolocation.<ref name="Geisler Colbert Carew 2014">{{Cite journal |last1=Geisler |first1=Jonathan H. |last2=Colbert |first2=Matthew W. |last3=Carew |first3=James L. |date=April 2014 |title=A new fossil species supports an early origin for toothed whale echolocation |url=https://www.nature.com/articles/nature13086 |journal=Nature |volume=508 |issue=7496 |pages=383–386 |doi=10.1038/nature13086 |pmid=24670659 |bibcode=2014Natur.508..383G |s2cid=4457391 |issn=1476-4687|url-access=subscription }}</ref> However, basal xenorophids lack cranial asymmetry, indicating that this likely evolved twice.<ref name="Coombs Clavel Park 2020"/> Extant odontocetes have asymmetric nasofacial regions; generally, the [[median plane]] is shifted to the left and structures on the right are larger.<ref name="Geisler Colbert Carew 2014"/> Both cranial telescoping and asymmetry likely relate to sound production for echolocation.<ref name="Churchill Geisler Beatty 2018"/>

==== Mechanism ====

[[File:Killer whale residents broadband.ogg |left|thumb|Southern Alaskan resident [[killer whale]]s 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&nbsp;kHz.<ref>{{cite journal |last1=Galatius |first1=Anders |last2=Olsen |first2=Morten Tange |last3=Steeman |first3=Mette Elstrup |last4=Racicot |first4=Rachel A. |last5=Bradshaw |first5=Catherine D. |last6=Kyhn |first6=Line A. |last7=Miller |first7=Lee A. |title=Raising your voice: evolution of narrow-band high-frequency signals in toothed whales (Odontoceti) |journal=Biological Journal of the Linnean Society |volume=166 |issue= 2 |pages=213–224 |date=2019 |doi=10.1093/biolinnean/bly194 |hdl=1983/dc8d8192-b8b6-4ec3-abd5-2ef84fddbee8 |hdl-access=free }}</ref>

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.<ref name="Kyhn, L.A. 2010">{{cite journal |last1=Kyhn |first1=L. A. |last2=Jensen |first2=F. H. |last3=Beedholm |first3=K. |last4=Tougaard |first4=J. |last5=Hansen |first5=M. |last6=Madsen |first6=P. T. |title=Echolocation in sympatric Peale's dolphins (''Lagenorhynchus australis'') and Commerson's dolphins (''Cephalorhynchus commersonii'') producing narrow-band high-frequency clicks |journal=The Journal of Experimental Biology |volume=213 |issue=11 |pages=1940–1949 |date=June 2010 |pmid=20472781 |doi=10.1242/jeb.042440 |doi-access=free }}</ref> 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.<ref name="Kyhn, L.A. 2010" />

{{Anchor |Mechanics of echolocation in whales}}

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 [[Whale_vocalization#Odontocete_whales|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.<ref>{{cite book |last=Cranford |first=T. W. |chapter=In Search of Impulse Sound Sources in Odontocetes |date=2000 |title=Hearing by Whales and Dolphins |series=Springer Handbook of Auditory Research series |volume=12 |pages=109–155 |editor1=Au, W. W. |editor2=Popper, A. N. |editor3=Fay, R. R. |publisher=Springer |location=New York |doi=10.1007/978-1-4612-1150-1_3 |isbn=978-1-4612-7024-9 }}</ref>

It has been suggested that the arrangement of the teeth of some smaller toothed whales may be an adaptation for echolocation.<ref>{{cite journal |last=Dobbins |first=P. |title=Dolphin sonar--modelling a new receiver concept |journal=Bioinspiration & Biomimetics |volume=2 |issue=1 |pages=19–29 |date=March 2007 |pmid=17671323 |doi=10.1088/1748-3182/2/1/003 |url=http://biomimetic.pbworks.com/f/Dolphin+sonar%E2%80%94modelling+a+new+receiverDobbins.pdf |bibcode=2007BiBi....2...19D |s2cid=27290079 }}</ref> 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.<ref>{{cite book |last1=Goodson |first1=A. D. |last2=Klinowska |first2=M. A. |date=1990 |chapter=A proposed echolocation receptor for the bottlenose dolphin (''Tursiops truncatus''): modeling the receive directivity from tooth and lower jaw geometry |title=Sensory Abilities of Cetaceans |volume=196 |editor1=Thomas, J. A. |editor2=Kastelein, R. A. |location=New York |publisher=Plenum |pages=255–267 |series=NATO ASI Series A }}</ref>

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.<ref>{{cite book |last=Ketten |first=D. R. |date=1992 |chapter=The Marine Mammal Ear: Specializations for aquatic audition and echolocation |title=The Evolutionary Biology of Hearing |url=https://archive.org/details/evolutionarybiol0000unse_r3h2 |url-access=registration |editor1=Webster, D. |editor2=Fay, R. |editor3=Popper, A. |publisher=Springer-Verlag |pages=[https://archive.org/details/evolutionarybiol0000unse_r3h2/page/717 717]–750 }}</ref><ref>{{cite book |last=Ketten |first=D. R. |date=2000 |chapter=Cetacean Ears |title=Hearing by Whales and Dolphins |editor1=Au, W. W. |editor2=Popper, A. N. |editor3=Fay, R. R. |series=SHAR Series for Auditory Research |publisher=Springer |pages=43–108 }}</ref>

=== Oilbirds and swiftlets ===

[[File:Palawan swiftlet (Aerodramus palawanensis) hunting by echolocation.JPG|thumb|A Palawan swiftlet (''Aerodramus palawanensis'') flies in complete darkness inside the Puerto Princesa subterranean river cave.]]

[[Oilbird]]s 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.<ref>{{cite book |title=Birds of the High Andes: a manual to the birds of the temperate zone of the Andes and Patagonia, South America |first1=Jon |last1=Fjeldså |first2=Niels |last2=Krabbe |publisher=Apollo Books |year=1990 |isbn=978-87-88757-16-3 |page=232 |url=https://books.google.com/books?id=NmXSeVrmlgIC&q=oilbird+echo+trees+caves+nocturnal&pg=PA232 }}</ref><ref>{{cite book |title=Exploring Life Biology |author=Marshall Cavendish |publisher=Marshall Cavendish |year=2000 |isbn=978-0-7614-7142-4 |page=547 |url=https://books.google.com/books?id=vC4cwlhjGxsC&q=swiftlet+echo+trees+caves+nocturnal&pg=PA547 }}</ref>

=== Terrestrial mammals ===

{{further|Shrews#Echolocation}}

Terrestrial mammals other than bats known or thought to echolocate include [[shrew]]s,<ref>{{cite journal |last1=Tomasi |first1=Thomas E. |year=1979 |title=Echolocation by the Short-Tailed Shrew ''Blarina brevicauda'' | journal=Journal of Mammalogy |volume=60 |issue=4 | pages=751–759 |doi=10.2307/1380190 | jstor=1380190 }}</ref><ref>{{Cite journal |last=Buchler |first=E. R. |date=November 1976 |title=The use of echolocation by the wandering shrew (Sorex vagrans) |url=https://linkinghub.elsevier.com/retrieve/pii/S0003347276800164 |journal=Animal Behaviour |volume=24 |issue=4 |pages=858–873 |doi=10.1016/S0003-3472(76)80016-4 |s2cid=53160608 |url-access=subscription }}</ref><ref name="Siemers">{{cite journal |last1=Siemers |first1=Björn M. |last2=Schauermann |first2=Grit |last3=Turni |first3=Hendrik |last4=von Merten |first4=Sophie |title=Why do shrews twitter? Communication or simple echo-based orientation |journal=Biology Letters |volume=5 |issue=5 |pages=593–596 |date=October 2009 |pmid=19535367 |pmc=2781971 |doi=10.1098/rsbl.2009.0378 }}</ref> the [[tenrec]]s of [[Madagascar]],<ref>{{cite journal |last=Gould |first=Edwin |title=Evidence for echolocation in the Tenrecidae of Madagascar |journal=Proceedings of the American Philosophical Society |volume=109 |issue=6 |year=1965 |pages=352–360 |jstor=986137 }}</ref> [[Chinese pygmy dormouse|Chinese pygmy dormice]],<ref>{{cite journal |last1=He |first1=Kai |last2=Liu |first2=Qi |last3=Xu |first3=Dong-Ming |last4=Qi |first4=Fei-Yan |last5=Bai |first5=Jing |last6=He |first6=Shui-Wang |last7=Chen |first7=Peng |last8=Zhou |first8=Xin |last9=Cai |first9=Wan-Zhi |last10=Chen |first10=Zhong-Zheng |last11=Liu |first11=Zhen |last12=Jiang |first12=Xue-Long |last13=Shi |first13=Peng |display-authors=3 |date=2021-06-18 |title=Echolocation in soft-furred tree mice |url=https://www.science.org/doi/10.1126/science.aay1513 |journal=Science |volume=372 |issue=6548 |pages=eaay1513 |doi=10.1126/science.aay1513 |pmid=34140356 |s2cid=235463083 |issn=0036-8075|url-access=subscription }}</ref> and [[solenodon]]s.<ref name="Eisenberg1966">{{cite journal |last1=Eisenberg |first1=J. F. |last2=Gould |first2=E. |year=1966 |title=The Behavior of ''Solenodon paradoxus'' in Captivity with Comments on the Behavior of other Insectivora |journal=[[Zoologica]] |volume=51 |issue=4 |pages=49–60 |df=dmy-all }}</ref> Shrew sounds, unlike those of bats, are low amplitude, broadband, multi-harmonic and frequency modulated.<ref name="Siemers"/> 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.<ref name="Siemers"/> There is evidence that blinded [[laboratory rats]] can use echolocation to navigate mazes.<ref>{{cite journal |last1=Riley |first1=Donald A. |last2=Rosenzweig |first2=Mark R. |title=Echolocation in Rats |journal=Journal of Comparative and Physiological Psychology |volume=50 |issue=4 |pages=323–328 |date=August 1957 |pmid=13475510 |doi=10.1037/h0047398 }}</ref>

== Countermeasures ==

[[File:Argema mimosae male.jpg|thumb|upright|The especially long tails on the hindwings of the [[Argema mimosae|African moon moth]], a [[Saturniidae|Saturniid]], oscillate in flight, deflecting the hunting bat's attack to the tails and thus enabling the moth to evade capture.<ref name="Rubin Hamilton 2018"/>]]

Some insects that are predated by bats have [[anti-predator adaptation]]s,  including predator avoidance,<ref name="Spangler 1988"/> attack deflection,<ref name="Rubin Hamilton 2018"/> and ultrasonic clicks which appear to function as warnings rather than [[echolocation jamming]].<ref name="Chiu Xian 2008"/><ref name="Phillips 2006">{{cite journal |last=Phillips |first=Kathryn |date=15 July 2006 |title=Are Moths Jamming or Warning? |journal=Journal of Experimental Biology |publisher=The Company of Biologists |volume=209 |issue=14 |page=i |doi=10.1242/jeb.02391 |issn=1477-9145 |s2cid=85257361}}</ref>

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''.<ref>{{Cite journal |last1=Corcoran |first1=Aaron J. |last2=Barber |first2=Jesse R. |last3=Conner |first3=William E. |date=2009-07-17 |title=Tiger Moth Jams Bat Sonar |url=https://www.science.org/doi/10.1126/science.1174096 |journal=Science |language=en |volume=325 |issue=5938 |pages=325–327 |doi=10.1126/science.1174096 |pmid=19608920 |bibcode=2009Sci...325..325C |s2cid=206520028 |issn=0036-8075|url-access=subscription }}</ref> 

Moth ultrasound can also function to [[Deimatic behaviour|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.<ref>{{Cite web |url=https://journals.biologists.com/jeb/article/212/14/2141/18292/Nai-ve-bats-discriminate-arctiid-moth-warning |title=Naïve bats discriminate arctiid moth warning sounds but generalize their aposematic meaning |access-date=2023-11-10 |website=journals.biologists.com}}</ref><ref>{{Cite journal |last1=Dowdy |first1=Nicolas J. |last2=Conner |first2=William E. |date=2016 |title=Acoustic Aposematism and Evasive Action in Select Chemically Defended Arctiine (Lepidoptera: Erebidae) Species: Nonchalant or Not? |journal=PLOS ONE |volume=11 |issue=4 |pages=e0152981 |doi=10.1371/journal.pone.0152981 |issn=1932-6203 |pmc=4838332 |pmid=27096408 |bibcode=2016PLoSO..1152981D |doi-access=free }}</ref>

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.<ref name="Spangler 1988">{{cite journal |last=Spangler |first=Hayward G. |date=1988 |title=Sound and the Moths That Infest Beehives |jstor=3495006 |journal=The Florida Entomologist |volume=71 |issue=4 |pages=467–477 |doi=10.2307/3495006 }}</ref> 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.<ref name="Rubin Hamilton 2018">{{cite journal |last1=Rubin |first1=Juliette J. |last2=Hamilton |first2=Chris A. |last3=McClure |first3=Christopher J. W. |last4=Chadwell |first4=Brad A. |last5=Kawahara |first5=Akito Y. |last6=Barber |first6=Jesse R. |display-authors=3 |title=The evolution of anti-bat sensory illusions in moths |journal=Science Advances |volume=4 |issue=7 |pages=eaar7428 |date=July 2018 |pmid=29978042 |pmc=6031379 |doi=10.1126/sciadv.aar7428 |bibcode=2018SciA....4.7428R }}</ref>

== See also ==

* [[Animal navigation]]
* [[Human echolocation]]
* [[Magnetoreception]]
* [[Ultrasound]]

== References ==

{{reflist}}

== Further reading ==

{{refbegin |30em}}
* {{cite book |last=Anderson |first=J. A. |date=1995 |title=An Introduction to Neural Networks |publisher=MIT Press |ref=none}}
* {{cite book |last=Au |first=W. E. |date=1993 |title=The Sonar of Dolphins |location=New York |publisher=Springer-Verlag |ref=none}} Provides a variety of findings on signal strength, directionality, discrimination, biology and more.
* {{cite journal |last1=Pack |first1=A. A. |last2=Herman |first2=L. M. |title=Sensory integration in the bottlenosed dolphin: immediate recognition of complex shapes across the senses of echolocation and vision |journal=The Journal of the Acoustical Society of America |volume=98 |issue=2 Pt 1 |pages=722–733 |date=August 1995 |pmid=7642811 |doi=10.1121/1.413566 |bibcode=1995ASAJ...98..722P |ref=none}} Shows evidence for the sensory integration of shape information between echolocation and vision, and presents the hypothesis of the existence of the mental representation of an "echoic image".
* {{citation |last=Hopkins |first=C. |date=2007 |title=Echolocation II |work=BioNB 424 Neuroethology Powerpoint presentation. |publisher=Cornell University |location=Ithaca, New York |ref=none}}
* {{cite journal |last1=Moss |first1=Cynthia F. |last2=Sinha |first2=S. R. |title=Neurobiology of echolocation in bats |journal=Current Opinion in Neurobiology |volume=13 |issue=6 |pages=751–758 |date=December 2003 |pmid=14662378 |doi=10.1016/j.conb.2003.10.016 |s2cid=8541198 |ref=none}}
* {{cite book |last1=Reynolds |first1=J. E. |last2=Rommel |first2=S. A. |date=1999 |title=Biology of Marine Mammals |publisher=Smithsonian Institution Press |ref=none}} 
* {{cite journal |last1=Surlykke |first1=A. |last2=Kalko |first2=E. K. |title=Echolocating bats cry out loud to detect their prey |journal=PLOS ONE |volume=3 |issue=4 |pages=e2036 |date=April 2008 |pmid=18446226 |pmc=2323577 |doi=10.1371/journal.pone.0002036 |bibcode=2008PLoSO...3.2036S |doi-access=free |ref=none}}
{{refend}}

== External links ==

* [http://www.hscott.net/the-dsp-behind-bat-echolocation/ The DSP Behind Bat Echolocation] - analysis of several kinds of bat echolocation
* [http://www.ibac.info/ International Bioacoustics Council] - links to many bioacoustics resources
* [http://www.bl.uk/listentonature British Library Sound Archive: Listen to Nature] {{Webarchive |url=https://web.archive.org/web/20160922002023/http://www.bl.uk/listentonature |date=2016-09-22 }} - has bat and swiftlet sonar signals
* [http://www.bio.bris.ac.uk/research/bats/index.htm Bat Ecology & Bioacoustics Lab] {{Webarchive |url=https://web.archive.org/web/20090526133837/http://www.bio.bris.ac.uk/research/bats/index.htm |date=2009-05-26 }}
* [http://www.bsos.umd.edu/psyc/batlab/ University of Maryland Bat Research Lab] - website of Cynthia Moss
* [http://neuroscience.brown.edu/simmonslab/ Batlab at Brown University] {{Webarchive |url=https://web.archive.org/web/20160723121038/http://neuroscience.brown.edu/simmonslab/ |date=2016-07-23 }} - JA Simmons Lab website
* [https://ppbio.inpa.gov.br/en/Bat_Library Morcegoteca] Program for Biodiversity Research (PPBio)

{{Neuroethology}}
{{hydroacoustics}}

{{Authority control}}

{{DEFAULTSORT:Animal Echolocation}}
[[Category:Ethology]]
[[Category:Neuroethology]]
[[Category:Hearing]]
[[Category:Senses]]
[[Category:Sonar]]
[[Category:Animal communication]]