Editing Animal echolocation (section)

==== 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>