Editing Shrew (section)

==Characteristics==
All shrews are tiny, most no larger than a mouse. The largest species is the [[Asian house shrew]] (''Suncus murinus'') of tropical Asia, which is about {{convert|15|cm|in|sigfig=1|abbr=on}} long and weighs around {{convert|100|g|oz|frac=2|abbr=on}}<ref>{{cite journal | vauthors = Louch CD, Ghosh AK, Pal BC | date = 1966 | title = Seasonal Changes in Weight and Reproductive Activity of Suncus murinus in West Bengal, India | journal = Journal of Mammalogy | volume = 47 | issue = 1 | pages = 73–78 | doi = 10.2307/1378070 | jstor = 1378070 | pmid = 5905563 }}</ref> The [[Etruscan shrew]] (''Suncus etruscus''), at about {{convert|3.5|cm|in|frac=8|abbr=on}} and {{convert|1.8|g|gr|0|abbr=off}}, is the smallest known living terrestrial mammal.
[[File:Watershrewskeleton.jpg|left|thumb|Water shrew skeleton]]
In general, shrews are terrestrial creatures that forage for seeds, insects, nuts, worms, and a variety of other foods in [[leaf litter]] and dense vegetation e.g. [[grass]], but some specialise in climbing trees, living underground, living [[Subnivean|under snow]], or even hunting in water. They have small eyes and generally poor [[Visual perception|vision]], but have excellent senses of [[hearing (sense)|hearing]] and [[olfaction|smell]].<ref name=EoM>{{cite book|veditors= Macdonald DW|vauthors= Barnard CJ|year= 1984|title= The Encyclopedia of Mammals|publisher= Facts on File|location= New York|pages= [https://archive.org/details/encyclopediaofma00mals_0/page/758 758–763]|isbn= 0-87196-871-1|url-access= registration|url= https://archive.org/details/encyclopediaofma00mals_0/page/758}}</ref> They are very active animals, with voracious appetites. Shrews have unusually high [[metabolic rate]]s, above that expected in comparable small mammals.<ref>{{cite journal|vauthors=William J, Platt WJ|date=1974|title=Metabolic Rates of Short-Tailed Shrews|journal=Physiological Zoology|volume=47|issue=2|pages=75–90|doi=10.1086/physzool.47.2.30155625|jstor=30155625|s2cid=87675441}}</ref> For this reason, they need to eat almost constantly like [[Mole (animal)|moles]]. Shrews in captivity can eat {{frac|1|2}} to 2 times their own body weight in food daily.<ref>{{cite book | vauthors = Reid F | date = 2009 | title = A Field Guide to the Mammals of Central America and Southeast Mexico | pages = 63–64 }}</ref>

They do not [[Hibernation|hibernate]], but some species are capable of entering [[torpor]]. In winter, many species undergo [[Morphology (biology)|morphological]] changes that drastically reduce their body weight. Shrews can lose between 30% and 50% of their body weight, shrinking the size of bones, skull, and internal organs.<ref>{{Cite book | url = https://books.google.com/books?id=z-XJ-UzdwIgC&q=seasonal+weight+changes+overwintering&pg=PA44 | title = The natural history of shrews | isbn = 978-0-8014-2595-0 | last1 = Churchfield | first1 = Sara | name-list-style = vanc | date = January 1990| publisher = Cornell University Press }}</ref>

Whereas rodents have gnawing [[incisor]]s that grow throughout life, the teeth of shrews wear down throughout life, a problem made more extreme because they lose their [[milk teeth]] before birth, so have only one set of teeth throughout their lifetimes. In some species, exposed areas of the teeth contain iron and are dark red. While this coloration was once thought to be caused by the iron, new research indicates this may not be the case.<ref>{{Cite journal |last=Srot |first=Vesna |last2=Houari |first2=Sophia |last3=Kapun |first3=Gregor |last4=Bussmann |first4=Birgit |last5=Predel |first5=Felicitas |last6=Pokorny |first6=Boštjan |last7=Bužan |first7=Elena |last8=Salzberger |first8=Ute |last9=Fenk |first9=Bernhard |last10=Kelsch |first10=Marion |last11=van Aken |first11=Peter A. |date=2024-04-30 |title=Ingenious Architecture and Coloration Generation in Enamel of Rodent Teeth |url=https://pubs.acs.org/doi/10.1021/acsnano.4c00578 |journal=ACS Nano |language=en |volume=18 |issue=17 |pages=11270–11283 |doi=10.1021/acsnano.4c00578 |issn=1936-0851}}</ref> Regardless, the iron reinforces the surfaces that are exposed to the most stress, which helps prolong the life of the teeth. This adaptation is not found in species with lower metabolism, which do not have to eat as much and therefore do not wear down the enamel to the same degree. The only other mammals' teeth with pigmented enamel are the incisors of rodents.<ref>{{cite web | first = John | last = Wible | name-list-style = vanc | url = https://carnegiemnh.org/shrews-dark-red-teeth/ | title = Why Do Some Shrews Have Dark Red Teeth? | date = 6 February 2018 | publisher = Carnegie Museum }}</ref> Apart from the first pair of incisors, which are long and sharp, and the chewing [[Molar (tooth)|molar]]s at the back of the mouth, the teeth of shrews are small and peg-like, and may be reduced in number. The [[Dentition#Dental formula|dental formula]] of shrews is:{{DentalFormula|upper=3.1.1-3.3|lower=1-2.0-1.1.3}}

Shrews are fiercely territorial, driving off rivals, and coming together only to mate. Many species dig [[burrow]]s for catching food and hiding from [[predator]]s, although this is not universal.<ref name=EoM/>

Female shrews can have up to 10 litters a year; in the tropics, they breed all year round; in temperate zones, they cease breeding only in the winter. Shrews have [[gestation]] periods of 17–32 days. The female often becomes pregnant within a day or so of giving birth, and [[lactation|lactates]] during her pregnancy, [[weaning]] one litter as the next is born.<ref name=EoM/> Shrews live 12 to 30 months.<ref>{{cite book | veditors = Macdonald DW | title = The Encyclopedia of Mammals | publisher = Oxford University Press | year = 2006 | isbn = 0-19-920608-2}}</ref>

A characteristic behaviour observed in many species of shrew is known as "caravanning". This is when a litter of young shrews form a line behind the mother, each gripping the shrew in front by the fur at the base of the tail.<ref>{{Citation |last=D'Agostino |first=Jennifer |title=Chapter 34 - Insectivores (Insectivora, Macroscelidea, Scandentia) |date=2015-01-01 |work=Fowler's Zoo and Wild Animal Medicine, Volume 8 |pages=275–281 |editor-last=Miller |editor-first=R. Eric |url=https://linkinghub.elsevier.com/retrieve/pii/B9781455773978000347 |access-date=2024-10-23 |place=St. Louis |publisher=W.B. Saunders |doi=10.1016/b978-1-4557-7397-8.00034-7 |isbn=978-1-4557-7397-8 |editor2-last=Fowler |editor2-first=Murray E.}}</ref>

Shrews are unusual among mammals in a number of respects. Unlike most mammals, some species of shrews are [[venom]]ous. Shrew venom is not conducted into the wound by [[fang]]s, but by grooves in the teeth. The venom contains various compounds, and the contents of the venom glands of the [[American short-tailed shrew]] are sufficient to kill 200 mice by intravenous injection. One chemical extracted from shrew venom may be potentially useful in the treatment of high blood pressure, while another compound may be useful in the treatment of some [[neuromuscular disease]]s and [[migraine]]s.<ref>{{cite book|title=Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals|first=Ross|last=Piper|publisher=[[Greenwood Press (publisher)|Greenwood Press]]|date=30 August 2007|isbn=978-0313339226}}</ref>{{better source needed|date=September 2020}} The saliva of the [[northern short-tailed shrew]] (''Blarina brevicauda'') contains [[soricidin]], a [[peptide]] which has been studied for use in treating [[ovarian cancer]].<ref>{{cite web | url = http://www.soricimed.com/news/bioprospecting-nb-inc%E2%80%99s-novel-ovarian-cancer-treatment-found-effective-animal-cancer-model | title = BioProspecting NB, Inc's novel ovarian cancer treatment found effective in animal cancer model. | access-date = 23 May 2010 | date = 8 Apr 2009 | archive-date = 16 July 2011 | archive-url = https://web.archive.org/web/20110716105212/http://www.soricimed.com/news/bioprospecting-nb-inc%E2%80%99s-novel-ovarian-cancer-treatment-found-effective-animal-cancer-model | url-status = dead }}</ref> Also, along with the [[bat]]s and [[toothed whale]]s, some species of shrews use [[Animal echolocation|echolocation]].<ref>{{Cite journal|last1=Chai|first1=Simin|last2=Tian|first2=Ran|last3=Rong|first3=Xinghua|last4=Li|first4=Guiting|last5=Chen|first5=Bingyao|last6=Ren|first6=Wenhua|last7=Xu|first7=Shixia|last8=Yang|first8=Guang|date=2020-02-25|title=Evidence of Echolocation in the Common Shrew from Molecular Convergence with Other Echolocating Mammals|journal=Zoological Studies|volume=59|issue=59 |pages=e4|doi=10.6620/ZS.2020.59-04|issn=1021-5506|pmc=7262541|pmid=32494297|s2cid=215414310}}</ref> Unlike most other mammals, shrews lack [[zygomatic bone]]s (also called the [[jugal]]s), so have incomplete [[zygomatic arch]]es.<ref>{{Cite news|title=About the mammalian skull, and be able to define and/or identify on a specimen all underlined terms.|url=https://www.d.umn.edu/~rmoen/Mammalogy_4764_2009/Handouts/Lab_01_Skull.pdf}}</ref>

===Echolocation===
[[File:NShortTailedShrew23.jpg|thumb|right|The [[northern short-tailed shrew]] is known to [[Animal echolocation|echolocate]].]]
The only terrestrial mammals known to [[Animal echolocation|echolocate]] are two genera (''[[Sorex]]'' and ''[[Blarina]]'') of shrews, the [[tenrec]]s of [[Madagascar]], [[bat]]s, and the [[solenodon]]s.<ref>{{Cite web |title=What is echolocation and which animals use it? |url=https://www.discoverwildlife.com/animal-facts/what-is-echolocation/ |access-date=2022-03-25 |website=Discover Wildlife |language=en}}</ref> These include the [[Common Shrew|Eurasian or common shrew]] (''Sorex araneus'') and the American [[vagrant shrew]] (''Sorex vagrans'') and [[northern short-tailed shrew]] (''Blarina brevicauda''). These shrews emit series of ultrasonic squeaks.<ref>{{cite journal |jstor=1380190 |pages=751–9 | vauthors = Tomasi TE |title=Echolocation by the Short-Tailed Shrew Blarina brevicauda |volume=60 |issue=4 |journal=Journal of Mammalogy |year=1979 |doi=10.2307/1380190}}</ref><ref name="Siemers">{{cite journal | vauthors = Siemers BM, Schauermann G, Turni H, von Merten S | title = Why do shrews twitter? Communication or simple echo-based orientation | journal = Biology Letters | volume = 5 | issue = 5 | pages = 593–6 | date = October 2009 | pmid = 19535367 | pmc = 2781971 | doi = 10.1098/rsbl.2009.0378 }}</ref> By nature the shrew sounds, unlike those of bats, are low-amplitude, broadband, multiharmonic, and frequency modulated.<ref name="Siemers"/> They contain no "echolocation clicks" with [[reverberation]]s and would seem to be used for simple, close-range spatial orientation. In contrast to bats, shrews use echolocation only to investigate their habitats rather than additionally to pinpoint food.<ref name="Siemers"/> <blockquote>
Except for large and thus strongly reflecting objects, such as a big stone or tree trunk, they probably are not able to disentangle echo scenes, but rather derive information on habitat type from the overall call reverberations. This might be comparable to human hearing whether one calls into a beech forest or into a reverberant wine cellar.<ref name="Siemers"/>
</blockquote>