Editing Animal echolocation (section)

=== 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>