Sciurini is a tribe that includes about forty species of squirrels, mostly from the Americas. It includes five living genera—the American dwarf squirrels, Microsciurus; the Bornean Rheithrosciurus; the widespread American and Eurasian tree squirrels of the genus Sciurus, which includes some of the best known squirrel species; the Central American Syntheosciurus; and the American red squirrels, Tamiasciurus. Like other arboreal squirrels, they are sometimes referred to as tree squirrels.
The name "Sciurini" was first employed by Hermann Burmeister in 1854, who used it for the entire squirrel family. In his influential 1945 classification of mammals, George Gaylord Simpson included four genera of squirrels in Sciurini, which he recognized as one of eight tribes within the subfamily Sciurinae (including all squirrels except the flying squirrels): Sciurus, Syntheosciurus, Microsciurus, and Sciurillus. He also classified Rheithrosciurus as "?Sciurini incertae sedis" (of uncertain placement). This grouping derives from Reginald Innes Pocock, who united these squirrels in 1923 as the subfamily Sciurinae.
In 1959, Joseph Curtis Moore published a review of the interrelationships of the squirrels. His definition of Sciurini was similar to Simpson's, but he no longer considered Rheithrosciurus to be incertae sedis. He noted that the members of Sciurini were united only by the possession of a special type of baculum (penis bone). He also divided the tribe into subtribes, producing the following classification:
- Tribe Sciurini
In their 1997 update to Simpson's classification, McKenna and Bell retained a similar definition for Sciurini, but also included several extinct genera, as follows:
- Tribe Sciurini
- Freudenthalia (fossil, early Miocene of Europe; assignment to Sciurini "uncertain")
- Plesiosciurus (fossil, middle Miocene of Asia)
- Subtribe Sciurina
- Douglassciurus (fossil, late Eocene of North America; McKenna and Bell used Douglassia, a preoccupied name replaced by Douglassciurus)
- Protosciurus (fossil, early Oligocene to early Miocene of North America)
- Miosciurus (fossil, early Miocene of North America)
- Sciurus (including Syntheosciurus)
- Subtribe Sciurillina
|Phylogeny of the squirrels.|
In the early 2000s, several studies were published using DNA sequences to study the interrelationships of squirrels. Two, published in 2003 and 2004 and both based on several different genes, produced largely concordant results, concluding that Sciurillus is not related to other Sciurini, but rather forms one of the most distinctive lineages of all squirrels; that Tamiasciurus is the closest relative to the other Sciurini; and that the group of Tamiasciurus and the other Sciurini is most closely related to the flying squirrels. The authors of the 2004 study formalized these results into a revised classification of squirrels. They removed Sciurillus from Sciurini, placed Tamiasciurus in it, and classified Sciurini with the flying squirrels (tribe Pteromyini) in a subfamily Sciurinae. Their classification was adopted in the 2005 third edition of Mammal Species of the World and remains current.
The same studies also provided insights into the interrelationships of genera within Sciurini. Microsciurus, Syntheosciurus, and Rheithrosciurus all appear among the various species of Sciurus included, making the latter genus paraphyletic; additionally, the two species of Microsciurus included in Mercer and Roth's 2003 study did not cluster with each other. A morphological study of Central American Sciurini also found that Microsciurus and Syntheosciurus are part of the Sciurus radiation, and suggested that Syntheosciurus be lumped into Sciurus while further work is needed on Microsciurus. In a 2008 monograph on Brazilian rodents, Bonvicino and others considered Guerlinguetus and Urosciurus, conventionally placed in Sciurus, as separate genera.
Douglassciurus, a fossil from the late Eocene (about 36 million years ago) of Wyoming, Montana, and Saskatchewan, is so similar to living Sciurus that the latter has been considered a living fossil. but some exclude this animal from the squirrel family because of several primitive characters. Emry and Korth, who re-described the animal in 1996, classified it within Sciurini and speculated that other squirrels may have evolved from animals similar to Sciurini squirrels. The Oligocene to early Miocene North American genera Protosciurus and Miosciurus are classified in Sciurini and may have given rise to the earliest known member of Sciurus, S. olsoni from the early late Miocene (about 10 million years ago) of Nevada. In Europe, Sciurus first appears early in the Pliocene. The 2005 discovery of S. olsoni provided evidence that the origin of the Sciurini lies in North America.
A Miocene squirrel from France and Spain, Freudenthalia, has been tentatively placed in Sciurini. Plesiosciurus from the Miocene of China has been interpreted as a member of Sciurini, but is unlikely to belong to the tribe.
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- Emry and Korth, 1996, p. 775
- Thorington and Hoffmann, 2005, p. 754
- Thorington and Ferrell, 2006, p. 18
- Burmeister, 1854, p. 145; McKenna and Bell, 1997, p. 122
- Simpson, 1945, p. 78
- Moore, 1959, p. 177
- Moore, 1959, pp. 177–178
- Moore, 1959, pp. 177–180
- Thorington and Hoffmann, 2005, p. 758
- McKenna and Bell, 1997, p. 122
- Emry and Korth, 2001
- Mercer and Roth, 2003; Steppan et al., 2004
- Steppan et al., 2004, p. 715
- Villalobos and Cervantes-Reza, 2007
- Bonvicino et al., 2008, pp. 15–16, 18
- Mercer and Roth, 2003, p. 1569; Emry and Korth, 1996, p. 775
- Thorington and Ferrell, 2006, p. 23
- Emry and Korth, 1996, p. 778
- Emry et al., 2005, p. 235
- Cuenca Bescós, 1988, p. 92; Aguilar, 2002, p. 388
- Emry et al., 2005, p. 228
- Aguilar, J.-P. 2002. Les sciuridés des gisements karstiques du Miocène inférieur à moyen du sud de la France : nouvelles espèces, phylogénie, paléoenvironnement (subscription required). Geobios 35:375–394 (in French).
- Bonvicino, C.R., Oliveira, J.A. and D'Andrea, P.S. 2008. Guia dos Roedores do Brasil, com chaves para gêneros baseadas em characteres externos. Série de Manuais Técnicos 11:1–120. Rio de Janeiro: Centro Pan-Americano de Febre Aftosa – OPAS/OMS (in Portuguese).
- Burmeister, H. 1854. Systematische Uebersicht der Thiere Brasiliens, welche während einer Reise durch die Provinzen von Rio de Janeiro und Minas geraës gesammelt oder beobachtet wurden. Erster Theil. Säugethiere (Mammalia). Berlin: G. Reimer (in German).
- Cuenca Bescós, G. 1988. Revisión de los Sciuridae del Aragoniense y del Rambliense en la fosa de Calatayud-Montalbán. Scripta Geologica 87:1–116 (in Spanish).
- Emry, R.J. and Korth, W.W. 1996. The Chadronian "Sciurus" jeffersoni Douglass, 1901: a new generic name, new material, and its bearing on the early evolution of Sciuridae (Rodentia). Journal of Vertebrate Paleontology 16:775–780.
- Emry, R.J. and Korth, W.V. 2001. Douglassciurus, new name for Douglassia Emry and Korth, 1996, not Douglassia Bartsch, 1934 (subscription required). Journal of Vertebrate Paleontology 21(5):400.
- Emry, R.J., Korth, W.W. and Bell, M.A. 2005. A tree squirrel (Rodentia, Sciuridae, Sciurini) from the Late Miocene (Clarendonian) of Nevada (subscription required). Journal of Vertebrate Paleontology 25(1):228–235.
- McKenna, M.C. and Bell, S.K. 1997. Classification of Mammals: Above the species level. New York: Columbia University Press, 631 pp. ISBN 978-0-231-11013-6
- Mercer, J.M. and Roth, V.L. 2003. The effects of Cenozoic global change on squirrel phylogeny (subscription required). Science 299:1568–1572.
- Moore, J.C. 1959. Relationships among the living squirrels of the Sciurinae. Bulletin of the American Museum of Natural History 118:157–206.
- Simpson, G.G. 1945. The principles of classification and a classification of mammals. Bulletin of the American Museum Natural History 85:1–350.
- Steppan, S.J., Storz, B.L. and Hoffmann, R.S. 2004. 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.
- Thorington, R.W., Jr. and Hoffmann, R.S. 2005. Family Sciuridae. Pp. 754–818 in Wilson, D.E. and Reeder, D.M. (eds.). Mammal Species of the World: a taxonomic and geographic reference. 3rd ed. Baltimore: The Johns Hopkins University Press, 2 vols., 2142 pp. ISBN 978-0-8018-8221-0
- Thorington, R.W. and Ferrell, K. 2006. Squirrels: the animal answer guide. Johns Hopkins University Press, 183 pp. ISBN 978-0-8018-8402-3
- Villalobos, F. and Cervantes-Reza, F. 2007. Phylogenetic relationships of Mesoamerican species of the genus Sciurus (Rodentia: Sciuridae). Zootaxa 1525:31–40.
Tree squirrels include over a hundred species found on all continents except Antarctica, and are the members of the squirrel family most commonly referred to as "squirrels". They do not form a single natural, or monophyletic, group, but instead are related to the various other animals in the squirrel family, including ground squirrels, flying squirrels, marmots, and chipmunks. The most well-known genus is Sciurus, which includes the eastern gray squirrel of North America, introduced to Great Britain, the red squirrel of Eurasia, and the fox squirrel, among many others.
Guy G. Musser, one of the world's leading experts on rodents, and the Archbold Curator Emeritus of Mammalogy at the American Museum of Natural History in New York City, clarifies the usage of "squirrel" and related terms:
The squirrel family includes ground squirrels, chipmunks, marmots, prairie dogs, and flying squirrels, but to most people squirrel refers to the 122 species of tree squirrels, which belong to 22 genera of the subfamily Sciurinae.
- Subfamily Ratufinae
- Genus Ratufa (Asian giant squirrels)
- Subfamily Sciurillinae
- Genus Sciurillus (South American pygmy squirrel)
- Subfamily Sciurinae
- Subfamily Callosciurinae (Asian tree squirrels)
- Genus Callosciurus (Oriental tree squirrels, introduced into Australia, Europe, and South America)
- Genus Exilisciurus (Asian pygmy squirrels)
- Genus Funambulus (Asian palm squirrels)
- Genus Glyphotes (sculptor squirrel)
- Genus Nannosciurus (Asian dwarf squirrel)
- Genus Prosciurillus (Sulawesi dwarf squirrels)
- Genus Rubrisciurus (Sulawesi giant squirrel)
- Genus Sundasciurus (Sunda squirrels)
- Genus Tamiops (Asian striped squirrels)
- Subfamily Xerinae
Relationship with humans
Squirrels are generally clever and persistent animals. In residential neighborhoods, they are notorious for eating out of bird feeders, digging in planting pots and flower beds to pull out bulbs which they chew on or to either bury or recover seeds and nuts and for inhabiting sheltered areas including attics and basements. Squirrels use their keen sense of smell to locate buried nuts and can dig extensive holes in the process. Birds, especially crows, often watch a squirrel bury a nut, then dig it up as soon as the squirrel leaves. Although expert climbers, and primarily arboreal, squirrels also thrive in urban environments, where they get used to humans. Their intelligence makes them suitable as pets.
Squirrels are sometimes considered pests because of their propensity to chew on various edible and inedible objects. This characteristic trait aids in maintaining sharp teeth, and because their teeth grow continuously, prevents over-growth. Homeowners in areas with a heavy squirrel population must keep attics and basements carefully sealed to prevent property damage caused by nesting squirrels. A squirrel nest is called a "drey". Some homeowners resort to more interesting ways of dealing with this problem, such as collecting and planting fur from pets such as domestic cats and dogs in attics. This fur will indicate to nesting squirrels that a potential predator roams and will encourage evacuation. Fake owls and scarecrows are generally ignored by the animals, and the best way to prevent chewing on an object is to coat it with something to make it undesirable: for instance a soft cloth or chili pepper paste or powder. Squirrel trapping is also practised to remove them from residential areas. However, otherwise squirrels are safe neighbors that pose almost zero risk of transmitting rabies.
Squirrels are often the cause of power outages. They can readily climb a power pole and crawl across a power line. The animals will climb onto transformers or capacitors looking for food. If they touch a high voltage conductor and a grounded portion of the device at the same time, they are then electrocuted and cause a short circuit that shuts down equipment. Squirrels have brought down the high-tech NASDAQ stock market twice and were responsible for a spate of power outages at the University of Alabama. To sharpen their teeth they will often chew on tree branches or even the occasional live power line. Rubber plates (squirrel guards) are sometimes used to prevent access to these facilities.
Squirrels are blamed for economic losses to homeowners, nut growers, forest managers in addition to damage to electric transmission lines. These losses include direct damage to property, repairs, lost revenue and public relations. While dollar costs of these losses are sometimes calculated for isolated incidents, there is no tracking system to determine the total extent of the losses.
Squirrels are also responsible for burrowing into sensitive earthworks such as dams and levees, causing a loss of structural integrity which requires diligent maintenance and prevention. Squirrel burrowing activity has sometimes resulted in catastrophic failures of these structures.
Squirrels can be trained to be hand-fed. Because they are able to cache surplus food, they take as much food as is available. Squirrels living in parks and campuses in cities have learned that humans are typically a ready source of food. Urban squirrels have learned to get a lot of food from generous humans. A commonly given food is peanuts, but recent studies show that raw peanuts contain a trypsin inhibitor that prevents the absorption of protein in the intestines. Therefore offering peanuts that have been roasted is the better option. However, wildlife rehabilitators in the field have noted that neither raw nor roasted peanuts nor sunflower seeds are healthy for squirrels, because they are deficient in several essential nutrients. This type of deficiency has been found to cause Metabolic Bone Disease, a somewhat common ailment found in malnourished squirrels.
Squirrels are occasionally kept as household pets, provided they are selected young enough and are hand raised in a proper fashion. They can be taught to do tricks, and are said to be as intelligent as dogs in their ability to learn behaviors. Pet squirrels are usually kept without cages, but a large cage and a balanced diet with good variety will keep a pet squirrel healthy and happy. The pet owner must beware of "spring fever" at which time a female pet squirrel will become very defensive of her cage, considering it her nest, and will become somewhat aggressive to defend the area.
Squirrel meat is considered a favored meat in certain regions of the United States where it can be listed as wild game. This is evidenced by extensive recipes for its preparation found in cookbooks, including older copies of The Joy of Cooking. Squirrel meat can be exchanged for rabbit or chicken in recipes, though it can have a gamey taste. Unlike the most game meat, the American Heart Association has found squirrel to be high in cholesterol.
In the U.S.
In many areas of the U.S., particularly areas of the American South, squirrels are hunted for food. Republican Presidential candidate Mike Huckabee mentioned his experiences eating squirrel during the South Carolina primary, saying that "When I was in college, we used to take a popcorn popper, because that was the only thing they would let us use in the dorm, and we would fry squirrels in a popcorn popper in the dorm room." He later told Meet the Press anchor Tim Russert that squirrel constitutes "a Southern delicacy". The Ramapough Mountain Indian Tribe of New Jesery considered eating squirrel to be a tradition.
In the U.K.
But in the early 21st century, wild squirrel has become a more popular meat to cook with, showing up in restaurants and shops more often in Britain as a fashionable alternative meat. Specifically, U.K. citizens are cooking with the invasive gray squirrel, which is being praised for its low fat content and the fact that it comes from free range sources. Additionally, the novelty of a meat considered unusual or special has added to the spread of squirrel consumption. Due to the difficulty of a clean kill and other factors, the majority of squirrel eaten in the U.K. is acquired from professional hunters, trappers, and gamekeepers.
Some Britons are eating the gray squirrel as a direct attempt to help the native red squirrel, which has been dwindling since the introduction of the gray squirrel in the 19th century. This factor was marketed by a national "Save Our Squirrels" campaign that used the slogan, “Save a red, eat a gray!”
Despite periodic complaints about the animal as a pest, general public opinion towards the animal is favorable, thanks to its agreeable appearance, intelligence and its eating styles and habits. Squirrels are popular characters in many forms of media, such as the literary works of Beatrix Potter, Brian Jacques' Redwall series (including Jess Squirrel and numerous other squirrels), Pattertwig in C. S. Lewis' Prince Caspian, Michael Tod's Woodstock Saga of novels featuring squirrel communities in the style of Watership Down, and the Starwife and her subjects from Robin Jarvis's Deptford novels. Squirrels are also popular characters in cartoons, such as Scrat from Ice Age, Slappy Squirrel of the Animaniacs, Sandy Cheeks from SpongeBob SquarePants, Hammy from Over the Hedge, Benny in The Wild, Rodney and Leon and Darlene from Squirrel Boy, Secret Squirrel, Screwy Squirrel, Nutty from Happy Tree Friends, and Rocky, Bullwinkle's adventuring partner. Grace from the webcomic El Goonish Shive is often pictured as an anthropomorphic squirrel, since it is her most natural and favored form. Video games such as Rare's Conker series starring Conker the Squirrel, as well as Ocean Software's Mr. Nutz. There is even a squirrel-themed super-heroine, Squirrel Girl.
Albino and white squirrels
One of the ways that squirrels impact human society is inspired by the fascination that people seem to have over local populations of white squirrels (often mis-identified as being albino). This manifests itself by the creation of social group communities that form from a commonly-shared interest in these rare animals. These groups demonstrate classic sociological group dynamics, including personal identity by belonging to a group, as well as hierarchical competition between white squirrel groups with each other over which has the best local white squirrel population. Other impacts on human society inspired by white squirrels include the creation of organizations that seek to protect them from human predation, and the use of the white squirrel image as a cultural icon.
Some examples of this cultural impact include:
- Olney, Illinois, known as the "White Squirrel Capital of the World," is home of the world's largest known white squirrel colony. These squirrels have the right of way on all streets in the town, with a $500 fine for hitting one. The Olney Police Department features the image of a white squirrel on its officers' uniform patches.
- Along with Olney, there are four other towns in North America that avidly compete with each other to be the official "Home of the White Squirrel", namely: Marionville, Missouri, Brevard, North Carolina, Exeter, Ontario, and Kenton, Tennessee, each of which holds an annual white squirrel festival, among other things designed to promote their claim of "White Squirrel Capital".
- Other towns that have reported white squirrel populations in North America (although not necessarily at war with other towns to be the "official" white squirrel capital) include Dayton, Ohio, DeForest, Wisconsin, and some of the snowbelt cities in the Western, Central and Finger Lakes regions of New York state (Buffalo, Rochester, and Syracuse).
In addition to the various towns that boast of their white squirrel populations, there also is a surprisingly large number of university campuses in North America that have white squirrels, including:
- The University of Texas at Austin, which has an Albino Squirrel Preservation Society, founded 2001, along with its sister chapter at University of North Texas. In 2006, the University of Texas at Austin held a student referendum to name their white squirrel as the university's secondary mascot, however the vote was narrowly defeated by the student body.
- Michigan Technological University in Houghton, Michigan is home to frequently-sighted white squirrels that live on and around the campus. A Facebook group dedicated to these squirrels, called I've Seen the Albino Squirrel of Michigan Tech, was created for people to post photographs and anecdotes of their encounters with the white squirrels, and includes some stories from Michigan Tech alumni that recall seeing white squirrels in Houghton dating back to the 1930s.
- The University of Louisville in Kentucky has established its own chapter of "The Albino Squirrel Preservation Society", which maintains contact with its members and interested parties through a Facebook group by that name. The university has an open policy to give away a free t-shirt to anyone who brings a photograph to the administration offices that was taken of an albino squirrel on campus grounds.
- Other university campuses that have albino squirrel populations include Ohio State University in Columbus, Ohio, Western Kentucky University in Bowling Green, Kentucky (which has had a population of albino squirrels since the 1960s), and Youngstown State University in Youngstown, Ohio.
Although these squirrels are commonly referred to as albinos, most of them are likely non-albino squirrels that exhibit a rare white fur coloration known as leucism that is as a result of a recessive gene found within certain Eastern gray squirrel (Sciurus carolinensis) populations, and so technically they ought to be referred to as white squirrels, instead of albino. Dr. Michael Stokes, a biology professor at Western Kentucky University, commented that the probable cause for the abundance of white squirrels on university campuses was due to them being originally introduced by someone:
We're not sure how they got here, but I'll tell you how it usually happens...When you see them, especially around a college campus or parks, somebody brought them in because they thought it would be neat to have white squirrels around.
Dr. Albert Meier, another biology professor at Western Kentucky University, added that:
... white squirrels rarely survive in the wild because they can't easily hide. But on a college campus, they are less likely to be consumed by other animals.
A list of white squirrel sightings around the world is maintained by the White Squirrel Research Institute, a group based in Brevard, North Carolina.
Red and gray squirrels in the UK
A decline of the red squirrel and the rise of the eastern gray squirrel has been widely remarked upon in British popular culture. It is mostly regarded as the invading grays driving out the native red species. Evidence also shows that gray squirrels are vectors of the Squirrel parapoxvirus for which no vaccine is presently available and which is deadly to red squirrels but does not seem to affect the host. Currently the red squirrel only resides in a few isolated areas of the UK, notably in Scotland, and in England Formby, the Lake District, Brownsea Island, and the Isle of Wight. Special measures are in place to contain and remove any infiltration of gray squirrels into these areas.
Under British law, the eastern gray squirrel is regarded as vermin, and at one point it was illegal to release any into the wild; any caught had to be either destroyed or kept captive. In 2008 the law was altered, allowing those with the proper license to release captured gray squirrels.
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