View source for Squirrel

{{short description|Family of rodents}}
{{About|the squirrel family (Sciuridae) as a whole}}
{{Pp-semi-indef|small=yes}}
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{{Use dmy dates|date=October 2020}}
{{Automatic taxobox
| name = Squirrels
| fossil_range = {{fossil range|Late Eocene|Recent|Late [[Eocene]] – Recent}}
| image = Sciuridae.jpg
| image_upright = 1.15
| image_caption = Various members of the family Sciuridae

{{aligned table|cols=3
 | ''[[Prevost's squirrel|Callosciurus prevostii]]'' | ''[[Siberian chipmunk|Eutamias sibiricus]]'' | ''[[American red squirrel|Tamiasciurus hudsonicus]]''
 | ''[[Fox squirrel|Sciurus niger]]'' | ''[[Urocitellus columbianus]]''  | ''[[Smith's bush squirrel|Paraxerus cepapi]]''
 | ''[[Cape ground squirrel|Geosciurus inauris]]'' | ''[[Marmot]]a'' sp.  | ''[[Black-tailed prairie dog|Cynomys ludovicianus]]''
}}
| taxon = Sciuridae
| authority = [[Johann Fischer von Waldheim|Fischer de Waldheim]], 1817
| type_genus = ''[[Sciurus]]''
| type_genus_authority = [[Carl Linnaeus|Linnaeus]], 1758
| subdivision_ranks = Subfamilies and tribes
| subdivision = * Subfamily [[Ratufinae]]
* Subfamily [[Sciurillinae]]
* Subfamily [[Sciurinae]]
** Tribe [[Sciurini]]
** Tribe [[Pteromyini]]
* Subfamily [[Callosciurinae]]
** Tribe [[Callosciurini]]
** Tribe [[Funambulini]]
* Subfamily [[Xerinae]]
** Tribe [[Xerini]]
** Tribe [[Protoxerini]]
** Tribe [[Marmotini]]
}}

'''Squirrels''' are members of the [[family (biology)|family]] '''Sciuridae''' ({{IPAc-en|s|I|'|j|u:|r|I|d|eI|,_|-|d|i:}}), a family that includes small or medium-sized [[rodent]]s. The squirrel family includes [[tree squirrel]]s, [[ground squirrel]]s (including [[chipmunk]]s and [[prairie dog]]s, among others), and [[flying squirrel]]s. Squirrels are indigenous to the Americas, Eurasia, and Africa, and were [[introduced species|introduced]] by humans to Australia.<ref name=Seebeck>{{cite web|last=Seebeck|first=J. H.|title=Sciuridae|url=http://www.scarysquirrel.org/vacation/australia/fauna.pdf|work=Fauna of Australia|access-date=2013-11-24|url-status=usurped|archive-url=https://web.archive.org/web/20150117031835/http://www.scarysquirrel.org/vacation/australia/fauna.pdf|archive-date=17 January 2015}}</ref> The earliest known fossilized squirrels date from the [[Eocene]] epoch, and among other living rodent families, the squirrels are most closely related to the [[mountain beaver]] and [[dormouse|dormice]].<ref>{{Cite journal |last1=Kay |first1=Emily H. |last2=Hoekstra |first2=Hopi E. |date=20 May 2008 |title=Rodents |journal=Current Biology |volume=18 |issue=10 |pages=R406–R410 |doi=10.1016/j.cub.2008.03.019 |pmid=18492466 |bibcode=2008CBio...18.R406K |issn=0960-9822}}</ref>

== Etymology ==
The word ''squirrel'', first attested in 1327, comes from the [[Anglo-Norman language|Anglo-Norman]] {{lang|xno|esquirel}} which is from the [[Old French]] {{lang|fro|escureil}},<ref name="OED1933_squirrel">{{Cite encyclopedia|title=Squirrel|encyclopedia=[[Oxford English Dictionary]]|year=1933|url=https://archive.org/details/in.ernet.dli.2015.120833/page/n368/mode/1up |via=[[Internet Archive]]|publisher=The Clarendon Press |publication-place=Oxford, UK |edition=1 Corrected re-issue |volume=10 (Sole–Sz) |page=749 |language=en}}</ref> the reflex of a [[Latin language|Latin]] word {{lang|la|sciurus}},<ref name="OED1933_squirrel"/> which was taken from the [[Ancient Greek]] word {{lang|grc|σκίουρος}} ({{transliteration|grc|skiouros}}; from {{lang|grc|σκία}} ('shade') and {{lang|grc|ουρα}} ('tail')),<ref name="OED1933_squirrel"/> referring to the long bushy tail which many of its members have.<ref>{{cite encyclopedia | encyclopedia =[[The Oxford English Dictionary]] | title = squirrel, ''n''. | url = http://dictionary.oed.com/cgi/entry/50235460 | access-date =8 November 2010 | edition = 2nd. | year = 1989 | publisher = Oxford University Press}}</ref>{{sfn|Whitaker|Elman|1980|p=370}} ''[[Sciurus]]'' is also the name of one of its genuses.{{sfn|Whitaker|Elman|1980|p=370}}

The [[Old English language|Old English]] word for the squirrel, {{lang|ang|ācweorna}}, survived into [[Middle English language|Middle English]] as {{lang|enm|aquerne}}<ref name="OED1913_aquerne">{{Cite encyclopedia|title=Aquerne|encyclopedia=[[Oxford English Dictionary]] |publisher=The Clarendon Press |publication-place=Oxford, UK |url=https://archive.org/details/in.ernet.dli.2015.99992/page/n460/mode/1up |via=[[Internet Archive]] |year=1913 |volume=1 (A–B) |edition=1 Corrected re-issue, 1970 reprint |page=422 |language=en}}</ref> before being replaced. The Old English word is of [[Common Germanic]] origin, [[cognate]]s of which are still used in other [[Germanic languages]], including the [[German language|German]] {{lang|de|Eichhörnchen}} (diminutive of {{lang|de|Eichhorn}},<ref name="OED1933_squirrel"/> which is not as frequently used); the [[Norwegian language|Norwegian]] {{lang|no|ikorn}}/{{lang|no|ekorn}}; the [[Dutch language|Dutch]] {{lang|nl|eekhoorn}}; the [[Swedish language|Swedish]] {{lang|sv|ekorre}} and the [[Danish language|Danish]] {{lang|da|egern}}.

A [[Terms of venery|group of]] squirrels is called a "dray"<ref>{{Cite book|last=Lipton|first=James|url=https://books.google.com/books?id=AVNazQEACAAJ|title=An Exaltation of Larks|date=1991|publisher=Viking|isbn=978-0-670-30044-0|language=en}}</ref> or a "scurry".<ref>''Universe in Your Pocket'' by Joel Levy, published by Barnes & Noble, Inc.</ref>

== Characteristics ==
[[File:Sciurus carolinensis -British Columbia, Canada-8.jpg|left|thumb|Reaching out for food on a garden bird feeder, this squirrel can rotate its hind feet, allowing it to descend a tree headfirst.]]
[[File:Ratufa skull.JPG|thumb|left|Skull of an [[Oriental giant squirrel]] (genus ''Ratufa'')—note the classic [[sciuromorphous]] shape of the anterior [[zygomatic arch|zygomatic]] region.]]

Squirrels are generally small animals, ranging in size from the [[African pygmy squirrel]] and [[least pygmy squirrel]] at {{cvt|10-14|cm}} in total length and just {{cvt|12-26|g}} in weight,<ref name=Kingdon1997>{{cite book | author=Kingdon, J. | author-link=Jonathan Kingdon | year=1997 | title=The Kingdon Guide to African Mammals | publisher=Academic Press Limited, London | isbn=0-12-408355-2 | url-access=registration | url=https://archive.org/details/kingdonfieldguid00jona }}</ref><ref name=Payne1998>{{cite book| author1=Payne, J. | author2=C.F. Francis | year=1998 | title=A Field Guide to the Mammals of Borneo | page=243 | publisher=The Sabah Society | edition=3 | isbn=967-99947-1-6 }}</ref> to the [[Bhutan giant flying squirrel]] at up to {{cvt|1.27|m}} in total length,<ref name=Choudhury2002>{{cite journal | author=Choudhury, A. | year=2002 | title=Petaurista nobilis singhei: First record in India and a note on its taxonomy | journal=The Journal of the Bombay Natural History Society | volume=99 | issue=1 | pages=30–34 }}</ref> and several [[marmot]] species, which can weigh {{cvt|8|kg}} or more.<ref name=Krystufek2013>{{cite journal | author1=Kryštufek, B. | author2=B. Vohralík | year=2013 | title=Taxonomic revision of the Palaearctic rodents (Rodentia). Part 2. Sciuridae: Urocitellus, Marmota and Sciurotamias | journal=Lynx, N. S. (Praha) | volume=44 | pages=27–138 }}</ref><ref name=Armitage2002>{{cite book | author1=Armitage, K.B. | author2=Blumstein, D.T. | year=2002 | chapter=Body-mass diversity in marmots. Holarctic marmots as a factor of biodiversity | editor1=K.B. Armitage | editor2=V.Yu. Rumiantsev | title=Holarctic Marmots as a Factor of Biodiversity | publisher=ABF Publishing House | pages=22–32 }}</ref> Squirrels typically have slender bodies with long, bushy tails and large eyes. In general, their [[fur]] is soft and silky, though much thicker in some species than others. The coat color of squirrels is highly variable between—and often even within—species.<ref>[http://www.wildlifeonline.me.uk/squirrels.html Tree Squirrels], ''Wildlife Online'', 23 November 2010.</ref>

In most squirrel species, the hind limbs are longer than the forelimbs, while all species have either four or five toes on each foot. The feet, which include an often poorly developed [[thumb]], have soft pads on the undersides<ref name=EoM>Milton (1984)</ref> and versatile, sturdy [[claw]]s for grasping and [[tree climbing|climbing]].<ref>{{cite web|url=http://animals.howstuffworks.com/mammals/squirrel-info.htm|title=Rodents|date=22 April 2008|publisher=How Stuff Works|access-date=30 December 2016}}</ref> [[Tree squirrels]], unlike most mammals, can descend a tree headfirst. They do so by rotating their ankles 180 degrees, enabling the hind feet to point backward and thus grip the tree bark from the opposite direction.<ref>{{cite book|last1=Thorington|first1=Richard W.|last2=Koprowski|first2=John L.|last3=Steele|first3=Michael A.|last4=Whatton|first4=James F.|year=2012|page=8|title=Squirrels of the World|publisher=Johns Hopkins University Press|isbn=978-1-4214-0469-1}}</ref>

=== Head ===
As their large eyes indicate, squirrels have excellent [[Visual perception|vision]], which is especially important for the tree-dwelling species. Many also have a good sense of [[somatosensory system|touch]], with [[whiskers|vibrissae]] on their limbs as well as their heads.<ref name=EoM />

The teeth of sciurids follow the typical rodent pattern, with large [[incisor]]s (for gnawing) that grow throughout life, and cheek teeth (for grinding) that are set back behind a wide gap, or [[diastema]]. The typical [[dentition|dental formula]] for sciurids is {{DentalFormula|upper=1.0.1.3|lower=1.0.1.3}}.<ref>''The Beginning of the Age of Mammals'' Kenneth D. Rose (2006) {{ISBN|978-0-801-88472-6}} p. 326</ref>

=== Tail ===
The purposes of squirrels' tails, to benefit the squirrel, include:<ref>{{Cite web|url=http://www.nutsaboutsquirrels.com/1695/why-do-squirrels-have-bushy-tails/|title=Why do squirrels have bushy tails? &#124; Nuts About Squirrels}}</ref>

* To keep rain, wind, or cold off itself.
* To cool off when hot, by pumping more blood through its tail.
* As a counterbalance when jumping about in trees
* As a [[parachute]] when jumping.
* To signal with.

The hairs from squirrel tails are prized in [[fly fishing]] when tying [[fishing flies]].<ref>{{Cite web |last=Genova |first=Cosmo |date=2022-01-11 |title=How to Preserve a Squirrel Pelt For Fly Tying |url=https://www.fieldandstream.com/fishing/preserve-squirrel-pelt-fly-tying/ |access-date=2024-06-01 |website=Field & Stream |language=en-US}}</ref> Squirrel hair is very fine, making it better for tying fishing flies.<ref>{{Cite book |last=Valla |first=Mike |url=https://books.google.com/books?id=0AVDDQAAQBAJ&dq=%22squirrel+tail%22+%22guard+hair%22&pg=PA45 |title=Tying and Fishing Bucktails and Other Hair Wings: Atlantic Salmon Flies to Steelhead Flies |date=2016-09-05 |publisher=Rowman & Littlefield |isbn=978-0-8117-6532-9 |language=en}}</ref>

When the squirrel sits upright, its tail folded up its back may stop predators looking from behind from seeing the characteristic shape of a small mammal.

== Lifetime ==
Squirrels live in almost every habitat, from tropical [[rainforest]] to semiarid [[desert]], avoiding only the high [[Polar regions of Earth|polar]] regions and the driest of deserts. They are predominantly [[herbivorous]], subsisting on seeds and nuts, but many will eat [[insects]] and even small vertebrates.<ref name="squirrels">[http://www.squirrels.org/faq.html Squirrel Place] {{webarchive|url=https://web.archive.org/web/20101227025300/http://www.squirrels.org/faq.html |date=27 December 2010 }}. squirrels.org. Retrieved 14 December 2010.</ref>

Many juvenile squirrels die in the first year of life. Adult squirrels can have a lifespan of 5 to 10 years in the wild. Some can survive 10 to 20 years in captivity.<ref>{{cite book|last1=Thorington|first1=Richard W.|last2=Koprowski|first2=John L.|last3=Steele|first3=Michael A.|last4=Whatton|first4=James F.|year=2012|page=12|title=Squirrels of the World|publisher=Johns Hopkins University Press|isbn=978-1-4214-0469-1}}</ref> Premature death may occur when a nest falls from the tree, in which case the mother may abandon her young if their body temperature is not correct. Many such baby squirrels have been rescued and fostered by a professional [[wildlife rehabilitator]] until they could be safely returned to the wild,<ref>{{cite web|url=http://www.squirrel-rehab.org/|title=Squirrel Rehab|access-date=19 August 2017}}</ref> although the density of squirrel populations in many places and the constant care required by premature squirrels means that few rehabilitators are willing to spend their time doing this and such animals are routinely [[animal euthanasia|euthanized]] instead.

<gallery widths="200px" heights="200px">
File:Squirrel enjoying in the sun.jpg|Squirrel in sunlight
File:Squirrel in Chandigarh.jpg|Squirrel in [[Chandigarh]]
File:Squirrel near Chandigarh.jpg|Squirrel near Chandigarh
File:Squirrel on mango tree.jpg|Squirrel on [[mango tree]]
</gallery>

== Behavior ==
[[File:Baby of squirrel.jpg|thumb|upright|Young squirrels, known as [[wikt:kit#Etymology_2|kits]]]]
Squirrels mate either once or twice a year and, following a [[gestation]] period of three to six weeks, give birth to a number of offspring that varies by species. The young are [[altricial]], being born naked, toothless, and blind. In most species of squirrel, the female alone looks after the young, which are [[weaning|weaned]] at six to ten weeks and become sexually mature by the end of their first year. In general, the ground-dwelling squirrel species are social, often living in well-developed colonies, while the tree-dwelling species are more solitary.<ref name=EoM />

Ground squirrels and tree squirrels are usually either [[Diurnality|diurnal]] or [[crepuscular]],<ref name=MassWild>{{cite web|title=Red & Gray Squirrels in Massachusetts|url=http://www.mass.gov/dfwele/dfw/wildlife/living/living_with_squirrels.htm|work=MassWildlife|publisher=Massachusetts Division of Fisheries and Wildlife|access-date=3 April 2012|archive-url=https://web.archive.org/web/20130517191120/http://www.mass.gov/dfwele/dfw/wildlife/living/living_with_squirrels.htm|archive-date=17 May 2013}}</ref> while the flying squirrels tend to be [[Nocturnality|nocturnal]]—except for lactating flying squirrels and their young, which have a period of diurnality during the summer.<ref>{{cite journal | last=Törmälä | first=Timo | author2=Vuorinen, Hannu | author3=Hokkanen, Heikki | year=1980 | title=Timing of circadian activity in the flying squirrel in central Finland | journal=Acta Theriologica | volume=25 | issue=32–42 | pages=461–474 | doi=10.4098/at.arch.80-42 | doi-access=free |issn = 0001-7051 }}</ref>

During hot periods, squirrels have been documented to [[splooting|sploot]], or lay their stomachs down on cool surfaces.<ref>{{cite web|last=McNamee|first=Kai|url=https://www.npr.org/2023/06/29/1185092056/squirrels-splooting-heat-wave-climate-change|title=The heat is making squirrels 'sploot' — a goofy act that signals something serious|publisher=[[NPR]]|date=June 29, 2023|access-date=August 8, 2023}}</ref>

Squirrels, like other rodents, employ species-specific strategies to store food, buffering against periods of scarcity.<ref name="Andersson Krebs 1978 pp. 707–711">{{cite journal | last1=Andersson | first1=Malte | last2=Krebs | first2=John | title=On the evolution of hoarding behaviour | journal=Animal Behaviour | volume=26 | year=1978 | issn=0003-3472 | doi=10.1016/0003-3472(78)90137-9 | pages=707–711| s2cid=53154232 }}</ref> In temperate regions, squirrels commonly cache nuts beneath leaf litter, inside hollow trees, or underground.<ref>{{cite journal | last1=HADJ-CHIKH | first1=LEILA Z. | last2=STEELE | first2=MICHAEL A. | last3=SMALLWOOD | first3=PETER D. | title=Caching decisions by grey squirrels: a test of the handling time and perishability hypotheses | journal=Animal Behaviour |  volume=52 | issue=5 | year=1996 | issn=0003-3472 | doi=10.1006/anbe.1996.0242 | pages=941–948| doi-access=free }}</ref> However, in subtropical and humid environments, traditional caching can lead to mold growth, decomposition, or premature germination.<ref name ="mould">{{cite journal | last1=Xiao | first1=Zhishu | last2=Gao | first2=Xu | last3=Zhang | first3=Zhibin | title=The combined effects of seed perishability and seed size on hoarding decisions by Pére David's rock squirrels | journal=Behavioral Ecology and Sociobiology |  volume=67 | issue=7 | date=2013-04-05 | issn=0340-5443 | doi=10.1007/s00265-013-1531-8 | pages=1067–1075| bibcode=2013BEcoS..67.1067X | s2cid=253815798 }}</ref> To counteract these challenges, some squirrels, particularly in subtropical zones, hang nuts or mushrooms on tree branches.<ref name ="mould">{{cite journal | last1=Xiao | first1=Zhishu | last2=Gao | first2=Xu | last3=Zhang | first3=Zhibin | title=The combined effects of seed perishability and seed size on hoarding decisions by Pére David's rock squirrels | journal=Behavioral Ecology and Sociobiology |  volume=67 | issue=7 | date=2013-04-05 | issn=0340-5443 | doi=10.1007/s00265-013-1531-8 | pages=1067–1075| bibcode=2013BEcoS..67.1067X | s2cid=253815798 }}</ref> This behavior, believed to minimize fungal infections and reduce the risk of food loss, also inadvertently aids certain trees, like [[Cyclobalanopsis]], in expanding their range, with forgotten or dislodged nuts sprouting in new locations, influencing forest ecology.<ref name="fix nut">{{cite journal | last1=Xu | first1=Han | last2=Xia | first2=Lian | last3=Spence | first3=John R | last4=Lin | first4=Mingxian | last5=Lu | first5=Chunyang | last6=Li | first6=Yanpeng | last7=Chen | first7=Jie | last8=Luo | first8=Tushou | last9=Li | first9=Yide | last10=Fang | first10=Suqin | title=Flying squirrels use a mortise-tenon structure to fix nuts on understory twigs | journal=eLife |  volume=12 | date=2023-06-13 | article-number=e84967 | issn=2050-084X | doi=10.7554/elife.84967| pmid=37309191 | pmc=10328505 | doi-access=free }}</ref> Two species of flying squirrel, the [[particolored flying squirrel]] and [[Hainan flying squirrel]] aid such cacheing by carving grooves into the nuts to fix the nuts tightly between small intersecting twigs, akin to the mortise-tenon joint in carpentry.<ref name="fix nut">{{cite journal | last1=Xu | first1=Han | last2=Xia | first2=Lian | last3=Spence | first3=John R | last4=Lin | first4=Mingxian | last5=Lu | first5=Chunyang | last6=Li | first6=Yanpeng | last7=Chen | first7=Jie | last8=Luo | first8=Tushou | last9=Li | first9=Yide | last10=Fang | first10=Suqin | title=Flying squirrels use a mortise-tenon structure to fix nuts on understory twigs | journal=eLife |  volume=12 | date=2023-06-13 | article-number=e84967 | issn=2050-084X | doi=10.7554/elife.84967| pmid=37309191 | pmc=10328505 | doi-access=free }}</ref>

=== Feeding ===
[[File:Squirrel, Manyara National Park, Tanzania (2010).jpg|thumb|right|Squirrel eating a fruit in [[Manyara National Park]], [[Tanzania]]]]
[[File:Squirrel in Seurasaari autumn.JPG|thumb|right|[[Red squirrel]] in the [[Seurasaari]] island in [[Helsinki]], [[Finland]]. The tame red squirrels on that island have become accustomed to humans thanks to their long-term feeding.<ref>Merja Laavola: Eläinten elintasosairaudet näkyvät Seurasaaressa. Vartti Etelä-Helsinki, Sanoma Kaupunkilehdet, 2010. (in Finnish)</ref>]]
[[File:Squirrel eating pumpkin seeds.webm|thumb|thumbtime=0|Squirrel retrieving and eating [[pumpkin]] seeds.]]

Because squirrels cannot digest [[cellulose]], they must rely on foods rich in [[protein]], [[carbohydrates]], and [[fat]]s. In [[temperate]] regions, early spring is the hardest time of year for squirrels because the nuts they [[Hoarding (animal behavior)|buried]] are beginning to sprout (and thus are no longer available to eat), while many of the usual food sources are not yet available. During these times, squirrels rely heavily on tree buds. Squirrels, being primarily [[herbivores]], eat a wide variety of plants, as well as [[nut (fruit)|nuts]], [[seed]]s, [[conifer cone]]s, [[fruit]]s, [[fungus|fungi]], and green [[vegetation]]. Some squirrels, however, also consume meat, especially when faced with hunger.<ref name="squirrels" /><ref>{{cite news |website=[[bbc.co.uk]] |access-date=13 July 2018 |url=http://news.bbc.co.uk/2/hi/4489792.stm |title=Russian squirrel pack 'kills dog' |date=1 December 2005}}</ref> Squirrels have been known to eat small [[bird]]s, young [[snake]]s, and smaller rodents, as well as [[bird egg]]s and [[insect]]s. Some [[tropical]] squirrel species have shifted almost entirely to a diet of insects.<ref>Richard W. Thorington, Katie Ferrell – [https://books.google.com/books?id=Y7cuEWCWpLMC&pg=PA75 ''Squirrels: the animal answer guide''], JHU Press, 2006, {{ISBN|0-8018-8402-0}}, {{ISBN|978-0-8018-8402-3}}, p. 75.</ref>

Squirrels, like [[pigeons]], [[feral cats]], and other fauna, are [[synanthropes]], in that they benefit and thrive from their interaction in human environments. This gradual process of successful interaction is called synurbanization, wherein squirrels lose their inherent fear of humans in an [[urban area|urban]] environment.<ref name="peim">{{cite journal |last1=Peiman |first1=Kathryn |title=Sublethal consequences of urban life for wild vertebrates |journal=Environmental Reviews |date=June 2016 |volume=24 |issue=4 |pages=416–425 |doi=10.1139/er-2016-0029|hdl=1807/74036 |hdl-access=free }}</ref> When squirrels were almost completely eradicated during the [[Industrial Revolution]] in [[New York City|New York]], they were later re-introduced to "entertain and remind" humans of nature. The squirrel blended into the urban environment so efficiently that when synanthropic behavior stops (e.g. people do not leave trash outside during particularly cold winters), they can become aggressive in their search for food.

Aggression and predatory behavior has been observed in various species of ground squirrels, in particular the [[thirteen-lined ground squirrel]].<ref>{{cite journal | last=Friggens | first=M. | title=Carnivory on Desert Cottontails by Texas Antelope Ground Squirrels | jstor=3672818 | journal=The Southwestern Naturalist | volume=47 | issue=1 | pages=132–133 | year=2002 | doi=10.2307/3672818| bibcode=2002SWNat..47..132F }}</ref> For example, Bernard Bailey, a scientist in the 1920s, observed a thirteen-lined ground squirrel preying upon a young [[chicken]].<ref>{{cite journal | last=Bailey | first=B. | title=Meat-eating propensities of some rodents of Minnesota | journal=Journal of Mammalogy | volume=4 | issue= 2| page=129 | year=1923 | doi = 10.1093/jmammal/4.2.129 }}</ref> Wistrand reported seeing this same species eating a freshly killed [[snake]].<ref>{{cite journal | last=Wistrand | first=E.H. | title=Predation on a Snake by ''Spermophilus tridecemlineatus'' | jstor=2424389 | journal=American Midland Naturalist | volume=88 | issue=2 | pages=511–512 | year=1972 | doi=10.2307/2424389}}</ref> Sometimes squirrels prey on an atypical animal: a pack of black squirrels in 2005 killed and ate a large stray [[dog]] in [[Lazo, Russia]].<ref name="bbcn">{{cite news |title=Russian Squirrel Pack Kills Dog |url=http://news.bbc.co.uk/2/hi/4489792.stm |website=BBC News |date=December 2005 |access-date=7 August 2020}}</ref> Squirrel attacks on humans are exceedingly rare.<ref name="bbc2">{{cite news |title=Cornwall squirrel 'pack' attacks boy, three |work=BBC News |date=14 July 2016 |url=https://www.bbc.com/news/uk-england-cornwall-36792959 |access-date=7 August 2020}}</ref><ref name="atl1">{{cite web |last1=Lafrance |first1=Adrienne |title=When Squirrels Attack – A cautionary tale |url=https://www.theatlantic.com/science/archive/2017/06/when-squirrels-attack/531129/ |website=The Atlantic |date=21 June 2017 |access-date=7 August 2020}}</ref>

Whitaker examined the stomachs of 139 thirteen-lined ground squirrels and found bird flesh in four of the specimens and the remains of a short-tailed [[shrew]] in one;<ref>{{cite journal | last=Whitaker | first=J.O. | title=Food and external parasites of ''Spermophilus tridecemlineatus'' in Vigo County, Indiana | jstor=1379067 | journal=Journal of Mammalogy | volume=53 | issue=3 | pages=644–648 | year=1972 | doi=10.2307/1379067}}</ref> Bradley, examining the stomachs of [[white-tailed antelope squirrel]]s, found at least 10% of his 609 specimens' stomachs contained some type of vertebrate, mostly [[lizard]]s and rodents.<ref>{{cite journal | last=Bradley | first=W. G. | title=Food habits of the antelope ground squirrel in southern Nevada | jstor=1377723 | journal=Journal of Mammalogy | volume=49 | issue=1 | pages=14–21 | doi=10.2307/1377723 | year=1968}}</ref> Morgart observed a white-tailed antelope squirrel capturing and eating a [[Perognathus flavus|silky pocket mouse]].<ref>{{cite journal | last=Morgart | first=J. R. | title=Carnivorous behavior by a white-tailed antelope ground squirrel ''Ammospermophilus leucurus'' | jstor=3670745 | journal=The Southwestern Naturalist | volume=30 | issue=2 | pages=304–305 | doi=10.2307/3670745 |date=May 1985| bibcode=1985SWNat..30..304M }}</ref>

== Taxonomy ==
[[File:One squirrel open mouth.jpg|thumb|A [[fox squirrel]] (''Sciurus niger'') outside the [[Cleveland Museum of Art]]]]
[[File:Taiwanrisu-2009.ogv|thumb|A squirrel (''Callosciurus erythraeus thaiwanensis'') in [[Japan]]]]
[[File:Prevostova vjeverica u Zagrebu.2.jpg|thumb|Three-coloured [[Prevost's Squirrel]] (''Callosciurus prevostii'') in [[Zagreb Zoo]], [[Croatia]]]]
{{further|List of sciurids}}
The living squirrels are divided into five [[subfamilies]], with about 58 [[genera]] and some 285 [[species]].<ref>{{cite journal|author1=Wilson, D.E. |author2=Reeder, D.M. | title=Class Mammalia Linnaeus, 1758. In: Zhang, Z.-Q. (Ed.) Animal biodiversity: An outline of higher-level classification and survey of taxonomic richness | journal=Zootaxa| volume=3148| year=2011| pages=56–60|doi=10.11646/zootaxa.3148.1.9 | url=http://mapress.com/zootaxa/2011/f/zt03148p060.pdf}}</ref> The oldest squirrel fossil, ''Hesperopetes'', dates back to the [[Chadronian]] (late [[Eocene]], about 40–35 [[million years ago]]) and is similar to modern flying squirrels.<ref>{{Cite journal | last1 = Emry | first1 = R. J. | last2 = Korth | first2 = W. W. | title = A new genus of squirrel (Rodentia, Sciuridae) from the mid-Cenozoic of North America | journal = Journal of Vertebrate Paleontology | volume = 27 | issue = 3 | pages = 693–698 | year = 2007 | doi = 10.1671/0272-4634(2007)27[693:ANGOSR]2.0.CO;2 | s2cid = 85847849 }}</ref>

A variety of fossil squirrels, from the latest [[Eocene]] to the [[Miocene]], have not been assigned with certainty to any living lineage. At least some of these probably were variants of the oldest [[basal (evolution)|basal]] "protosquirrels" (in the sense that they lacked the full range of living squirrels' [[autapomorphy|autapomorphies]]). The distribution and diversity of such ancient and ancestral forms suggest the squirrels as a group may have originated in North America.<ref name = tolweb>Steppan & Hamm (2006)</ref>

Apart from these sometimes little-known fossil forms, the [[phylogeny]] of the living squirrels is fairly straightforward. The three main lineages are the [[Ratufinae]] (Oriental giant squirrels), Sciurillinae and all other subfamilies. The Ratufinae contain a mere handful of living species in tropical [[Asia]]. The [[Neotropical Pygmy Squirrel|neotropical pygmy squirrel]] of tropical [[South America]] is the sole living member of the Sciurillinae. The third lineage, by far the largest, has a near-cosmopolitan distribution. This further supports the hypothesis that the common ancestor of all squirrels, living and fossil, lived in North America, as these three most ancient lineages seem to have [[evolutionary radiation|radiated]] from there; if squirrels had originated in [[Eurasia]], for example, one would expect quite ancient lineages in [[Africa]], but African squirrels seem to be of more recent origin.<ref name = tolweb />

The main group of squirrels can be split into five subfamilies: the [[Callosciurinae]], 60 species mostly found in [[South East Asia]]; the [[Ratufinae]], 4 cat-sized species found in [[South Asia|south]] and [[southeast Asia]]; the [[Sciurinae]], which contains the [[flying squirrel]]s (Pteromyini) and the [[Sciurini|tree squirrels]], 83 species found worldwide;<ref>Steppan, S. J. B. L. Storz, and R. S. Hoffmann. 2004. [http://www.bio.fsu.edu/~steppan/Steppan_et_al_Sciuridae.pdf Nuclear DNA phylogeny of the squirrels (Mammalia: Rodentia) and the evolution of arboreality from c-myc and RAG1]. Molecular Phylogenetics and Evolution, 30:703-719.</ref> [[Sciurillinae]], a single [[South America]]n species; and [[Xerinae]], which includes three [[Tribe (biology)|tribes]] of mostly terrestrial squirrels, including the [[Marmotini]] ([[marmot]]s, [[chipmunk]]s, [[prairie dog]]s, and other [[Holarctic]] ground squirrels), [[Xerini]] (African and some Eurasian ground squirrels), and [[Protoxerini]] (African tree squirrels).

=== Taxonomy list ===

* [[Basal (evolution)|Basal]] and ''[[incertae sedis]]'' Sciuridae (all [[fossil]])
** ''[[Hesperopetes]]''
** ''[[Kherem (genus)|Kherem]]''
** ''[[Lagrivea]]''
** ''[[Oligosciurus]]''
** ''[[Plesiosciurus]]''
** ''[[Prospermophilus]]''
** ''[[Sciurion]]''
** ''[[Similisciurus]]''
** ''[[Sinotamias]]''
** ''[[Vulcanisciurus]]''
* Subfamily [[Cedromurinae]] (fossil)
* Subfamily [[Ratufinae]] – Oriental giant squirrels (1 genus, 4 species)
* Subfamily [[Sciurillinae]] – neotropical pygmy squirrel ([[monotypic]])
* Subfamily [[Sciurinae]]
** Tribe [[Sciurini]] – tree squirrels (5 genera, about 38 species)
** Tribe [[Pteromyini]] – true flying squirrels (15 genera, about 45 species)
* Subfamily [[Callosciurinae]] – Asian ornate squirrels
** Tribe [[Callosciurini]] (13 genera, nearly 60 species)
** Tribe [[Funambulini]] palm squirrels (1 genus, 5 species)
* Subfamily [[Xerinae]] – terrestrial squirrels
** Tribe [[Xerini]] – spiny squirrels (3 genera, 6 species)
** Tribe [[Protoxerini]] (6 genera, about 50 species)
** Tribe [[Marmotini]] – ground squirrels, marmots, chipmunks, prairie dogs, etc. (6 genera, about 90 species)

{{cladogram|align=left|clades={{Clade|style=width:24em;
|label1='''[[Sciuridae]]'''<ref name="cladogram1">{{cite journal |last=Sheets |first=A. D. |last2=Chavez |first2=A. S. |title=Evolution of Pelage Luminance in Squirrels (Sciuridae) |journal=[[Frontiers in Ecology and Evolution]] |volume=8 |date=2020 |issue=249 |doi=10.3389/fevo.2020.00249 |doi-access=free}}</ref>
<ref name="cladogram2">{{cite journal |last=Hawkins |first=M. T. R. |last2=Leonard |first2=J. A. |last3=Helgen |first3=K. M. |last4=McDonough |first4=M. M. |last5=Rockwood |first5=L. L. |last6=Maldonado |first6=J. E. |title=Evolutionary history of endemic Sulawesi squirrels constructed from UCEs and mitogenomes sequenced from museum specimens |journal=[[BMC Evolutionary Biology]] |volume=16 |issue=1 |date=2016 |doi=10.1186/s12862-016-0650-z |doi-access=free|hdl=10261/132111 |hdl-access=free |pmc=4831120 }}</ref>
<ref name="cladogram3">{{cite journal |last=Arbogast |first=B. S. |title=A Brief History of the New World Flying Squirrels: Phylogeny, Biogeography, and Conservation Genetics |journal=[[Journal of Mammalogy]] |volume=88 |issue=4 |date=2007 |doi=10.1644/06-mamm-s-322r1.1 |doi-access=free |pages=840–849}}</ref>
<ref name="cladogram4">{{cite journal |last=Helgen |first=K. M. |last2=Cole |first2=F. R. |last3=Helgen |first3=L. E. |last4=Wilson |first4=D. E. |title=Generic Revision in the Holarctic Ground Squirrel Genus ''Spermophilus'' |journal=[[Journal of Mammalogy]] |volume=90 |issue=2 |date=2009 |doi=10.1644/07-mamm-a-309.1 |doi-access=free |pages=270–305}}</ref>
|1={{clade
  |1={{clade
    |1={{clade
      |1={{clade
        |label1=[[Sciurinae]]&nbsp;&nbsp;
        |1={{clade
          |label1=[[Pteromyini]]&nbsp;&nbsp;
          |1={{clade
            |1={{clade
              |1=''[[Eoglaucomys]]''
              |2={{clade
                |1=''[[Glaucomys]]''
                |2={{clade
                  |1=''[[Iomys]]''
                  |2={{clade
                    |1=''[[Hylopetes]]''
                    |2=''[[Petaurillus]]''
                    |3=''[[Petinomys]]''
                    }}
                  }}
                }}
              }}
            |2={{clade
              |1=''[[Petaurista]]''
              |2={{clade
                |1={{clade
                  |1=''[[Pteromys]]''
                  |2={{clade
                    |1=''[[Aeromys]]''
                    |2=''[[Biswamoyopterus]]''
                    |3=''[[Eupetaurus]]''
                    }}
                  }}
                |2={{clade
                  |1=''[[Pteromyscus]]''
                  |2={{clade
                    |1=''[[Belomys]]''
                    |2={{clade
                      |1=''[[Aeretes]]''
                      |2=''[[Trogopterus]]''
                      }}
                    }}
                  }}
                }}
              }}
            }}
          |label2=[[Sciurini]]&nbsp;&nbsp;
          |2={{clade
            |1=''[[Tamiasciurus]]''
            |2={{clade
              |1=''[[Rheithrosciurus]]''
              |2={{clade
                |1=''[[Sciurus]]''
                |2=''[[Microsciurus]]''
                |3=''[[Syntheosciurus]]''
                }}
              }}
            }}
          }}
        }}
      |2={{clade
        |label1=[[Callosciurinae]]&nbsp;&nbsp;
        |1={{clade
          |label1=[[Callosciurini]]&nbsp;&nbsp;
          |1={{clade
            |1=''[[Exilisciurus]]''
            |2={{clade
              |1=''[[Menetes]]''
              |2=''[[Rhinosciurus]]''
              }}
            |3={{clade
              |1=''[[Callosciurus]]''
              |2={{clade
                |1=''[[Nannosciurus]]''
                |2={{clade
                  |1=''[[Lariscus]]''
                  |2=''[[Sundasciurus]]''
                  }}
                }}
              }}
            |4={{clade
              |1=''[[Hyosciurus]]''
              |2={{clade
                |1=''[[Prosciurillus]]''
                |2=''[[Rubrisciurus]]''
                }}
              }}
            |5={{clade
              |1=''[[Dremomys]]''
              |2=''[[Glyphotes]]''
              |3=''[[Tamiops]]''
              }}
            }}
          |label2=[[Funambulini]]&nbsp;&nbsp;
          |2=''[[Funambulus]]''
          }}
        |label2=[[Xerinae]]&nbsp;&nbsp;
        |2={{clade
          |1={{clade
            |label1=[[Xerini]]&nbsp;&nbsp;
            |1={{clade
              |1=''[[Spermophilopsis]]''
              |2={{clade
                |1=''[[Atlantoxerus]]''
                |2=''[[Xerus]]''
                }}
              }}
            }}
          |2={{clade
            |label1=[[Marmotini]]&nbsp;&nbsp;
            |1={{clade
              |1={{clade
                |1=''[[Sciurotamias]]''
                |2={{clade
                  |1=''[[Eutamias]]''
                  |2=''[[Neotamias]]''
                  |3=''[[Tamias]]''
                  }}
                }}
              |2={{clade
                |1={{clade
                  |1=''[[Ammospermophilus]]''
                  |2=''[[Notocitellus]]''
                  }}
                |2={{clade
                  |1={{clade
                    |1=''[[Callospermophilus]]''
                    |2=''[[Otospermophilus]]''
                    }}
                  |2={{clade
                    |1=''[[Marmota]]''
                    |2={{clade
                      |1=''[[Spermophilus]]''
                      |2={{clade
                        |1=''[[Urocitellus]]''
                        |2={{clade
                          |1=''[[Ictidomys]]''
                          |2={{clade
                            |1=''[[Poliocitellus]]''
                            |2={{clade
                              |1=''[[Cynomys]]''
                              |2=''[[Xerospermophilus]]''
                              }}
                            }}
                          }}
                        }}
                      }}
                    }}
                  }}
                }}
              }}
            |label2=[[Protoxerini]]&nbsp;&nbsp;
            |2={{clade
              |1=''[[Heliosciurus]]''
              |2={{clade
                |1=''[[Epixerus]]''
                |2=''[[Funisciurus]]''
                |3=''[[Myosciurus]]''
                |4=''[[Paraxerus]]''
                |5=''[[Protoxerus]]''
                }}
              }}
            }}
          }}
        }}
      }}
    |2={{clade
      |label1=[[Sciurillinae]]&nbsp;&nbsp;
      |1=''[[Sciurillus]]''
      }}
    }}
  |2={{clade
    |label1=[[Ratufinae]]&nbsp;&nbsp;
    |1=''[[Ratufa]]''
    }}
  }}
}}}}
{{clear}}

== Relationship with humans ==
{{main|Tree squirrel#Relationship with humans}}

== See also ==
{{Portal|Mammals}}
* [[List of animal names#squirrel]]
* [[Variant Creutzfeldt–Jakob disease]] ([[Kuru (disease)|Kuru]]) from eating squirrel brains.<ref>{{cite news |last1=Blakeslee |first1=Sandra |title=Kentucky Doctors Warn Against a Regional Dish: Squirrels' Brains |url=https://www.nytimes.com/1997/08/29/us/kentucky-doctors-warn-against-a-regional-dish-squirrels-brains.html |access-date=18 April 2019 |newspaper=[[The New York Times]] |date=29 August 1997}}</ref><ref>{{cite web |url=https://www.livescience.com/63831-squirrel-brains-rare-disorder-creutzfeldt-jakob-disease.html |title=Man Dies from Extremely Rare Disease After Eating Squirrel Brains |first1=Rachael |last1=Rettner |date=October 15, 2018 |publisher=[[LiveScience]] |access-date=April 9, 2022}}</ref>

{{Anchor|Notes|reason="Notes" is the old section name, which was changed to "References" on 6 June 2018}}

== References ==
{{Reflist|30em}}

{{Anchor|References|reason="References" is the old section name, which was changed to "Further reading" on 6 June 2018}}

==Sources==
* {{cite book| last1 = Whitaker | first1= John O. Jr. |last2= Elman|first2=Robert|date=1980|title=The Audubon Society Field Guide to North American Mammals|edition=2nd|publisher=Alfred A. Knopf, Jr.| location = New York|isbn=0-394-50762-2}}

== Further reading ==
* Milton, Katherine (1984): "Family Sciuridae". In: Macdonald, D. (ed.): ''The Encyclopedia of Mammals'': 612–623. Facts on File, New York. {{ISBN|0-87196-871-1}}.
* Steppan, Scott J. and Hamm, Shawn M. (2006): [[Tree of Life Web Project]] – [http://tolweb.org/Sciuridae/16456/2006.05.13 "Sciuridae (Squirrels)"]. Version of 13 May 2006. Retrieved 10 December 2007.
* {{Cite journal | last1 = Steppan | first1 = S. J. | last2 = Storz | first2 = B. L. | last3 = Hoffmann | first3 = R. S. | doi = 10.1016/S1055-7903(03)00204-5 | title = Nuclear DNA phylogeny of the squirrels (Mammalia: Rodentia) and the evolution of arboreality from c-myc and RAG1 | journal = Molecular Phylogenetics and Evolution | volume = 30 | issue = 3 | pages = 703–719 | year = 2004 | pmid =  15012949| bibcode = 2004MolPE..30..703S }}
* Thorington, R.W. and Hoffmann, R.S. (2005): "Family Sciuridae". In: ''Mammal Species of the World: A Taxonomic and Geographic Reference'': 754–818. Johns Hopkins University Press, Baltimore.

== External links ==
{{Commons|Sciuridae}}
{{Wikispecies|Sciuridae}}
{{Wiktionary|squirrel}}
* {{wikiquote-inline}}
* [http://tolweb.org/Sciuridae/16456 Tree of Life: Sciuridae]
* [http://northernbushcraft.com/animalTracks/squirrel/notes.htm Squirrel Tracks]: How to identify squirrel tracks in the wild
* [https://web.archive.org/web/20070614105921/http://animals.nationalgeographic.com/animals/mammals/squirrel.html National Geographic link on Squirrels]
* [https://web.archive.org/web/20131206211135/http://squirrels.org/names.html List of names of squirrel taxa]

{{Rodents}}
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{{S. Callosciurinae nav}}
{{S. Sciurinae1 nav}}
{{S. Sciurinae2 nav}}
{{S. Xerinae nav}}
{{Marmotini nav}}
{{Taxonbar|from=Q9482}}
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[[Category:Squirrels| ]]
[[Category:Sciuromorpha]]
[[Category:Articles containing video clips]]
[[Category:Extant Eocene first appearances]]
[[Category:Rodents by common name]]
[[Category:Taxa named by Gotthelf Fischer von Waldheim]]