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Rodentia (rats & rodents)
Sciuridae
EOL Text
Squirrels are known from the end of the Eocene in Wyoming and the early Oligocene in southern France.
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Most squirrels eat mainly tree seeds and fruit, but their diet is diverse, including insects, eggs, fungi, lichens, and small vertebrates. While some squirrels consume fungi as a secondary component of their diet, it makes up nearly half of the diet of other species. Many species opportunistically take animal prey, such as the young and eggs of birds or other mammals. Foods such as buds, shoots, flowers, bark, lichens, and green plant material have generally low energy content per unit weight and make up a smaller portion of the diet. But the amount of each type of food consumed is determined mainly by its availability and accessibility. For this reason, diet composition changes from region to region, season to season, and year to year. Many squirrel species cache or hoard food as well.
Foraging Behavior: stores or caches food
Primary Diet: carnivore (Eats terrestrial vertebrates, Eats eggs, Insectivore ); herbivore (Frugivore , Granivore ); omnivore ; mycophage
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Squirrels are members of the family Sciuridae, consisting of small or medium-size rodents. The family includes tree squirrels, ground squirrels, chipmunks, marmots (including woodchucks), flying squirrels, and prairie dogs. Squirrels are indigenous to the Americas, Eurasia, and Africa, and have been introduced to Australia.[1] The earliest known squirrels date from the Eocene and are most closely related to the mountain beaver and to the dormouse among living rodent families.
Contents
Etymology[edit]
The word "squirrel", first specified in 1327, comes from Anglo-Norman esquirel from the Old French escurel, the reflex of a Latin word sciurus. This Latin word was borrowed from the Ancient Greek word σκίουρος, skiouros, which means shadow-tailed, referring to the bushy appendage possessed by many of its members.[2][3]
The native Old English word for the squirrel, ācweorna, survived only into Middle English (as aquerne) before being replaced.[4] The Old English word is of Common Germanic origin, and cognates used by other countries to name the squirrel include the German Eichhörnchen (diminutive of Eichhorn, which is not used), the Norwegian ikorn/ekorn, the Dutch eekhoorn, the Swedish ekorre and the Danish egern.
Characteristics[edit]
Squirrels are generally small animals, ranging in size from the African pygmy squirrel at 7–10 cm (2.8–3.9 in) in length and just 10 g (0.35 oz) in weight, to the Alpine marmot, which is 53–73 cm (21–29 in) long and weighs from 5 to 8 kg (11 to 18 lb). Squirrels typically have slender bodies with bushy tails and large eyes. In general, their fur is soft and silky, although much thicker in some species than others. The color of squirrels is highly variable between—and often even within—species.[5]
In general, the hind limbs are longer than the fore limbs, and they have four or five toes on each paw. Their paws include an often poorly developed thumb, and have soft pads on the undersides.[6] Unlike most mammals, Tree squirrels can descend a tree head-first. They do so by rotating their ankles 180 degrees so the hind paws are backward-pointing and can grip the tree bark.[7]
Squirrels live in almost every habitat from tropical rainforest to semiarid desert, avoiding only the high 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.[8]
As their large eyes indicate, in general squirrels have an excellent sense of vision, which is especially important for tree-dwelling species. They also have very versatile and sturdy claws for grasping and climbing.[9] Many also have a good sense of touch, with vibrissae on their heads and limbs.[6]
The teeth of sciurids follow the typical rodent pattern, with large gnawing incisors that grow throughout life, and grinding cheek teeth set back behind a wide gap, or diastema. The typical dental formula for sciurids is 1.0.1.31.0.1.3[citation needed]
Most 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.[10]
Behavior[edit]
Squirrels breed once or twice a year and give birth to a varying number of young after three to six weeks, depending on species. The young are born naked, toothless, and blind. In most species of squirrel, only the female looks after the young, which are weaned at around six to ten weeks of age and become sexually mature at the end of their first year. In general, ground-dwelling species are social animals, often living in well-developed colonies, but the tree-dwelling species are more solitary.[6]
Ground and tree squirrels are typically diurnal or crepuscular,[11] while flying squirrels tend to be nocturnal—except for lactating flying squirrels and their offspring, which have a period of diurnality during the summer.[12]
Feeding[edit]
Squirrels cannot digest cellulose, so they must rely on foods rich in protein, carbohydrates, and fats. In temperate regions, early spring is the hardest time of year for squirrels, because buried nuts begin to sprout and are no longer available for the squirrel to eat, and new food sources have not become available yet. During these times, squirrels rely heavily on the buds of trees. Squirrels' diets consist primarily of a wide variety of plants, including nuts, seeds, conifer cones, fruits, fungi, and green vegetation. However, some squirrels also consume meat, especially when faced with hunger.[8] Squirrels have been known to eat insects, eggs, small birds, young snakes, and smaller rodents. Indeed, some tropical species have shifted almost entirely to a diet of insects.[13]
Predatory behavior has been noted by various species of ground squirrels, in particular the thirteen-lined ground squirrel.[14] For example, Bailey, a scientist in the 1920s, observed a thirteen-lined ground squirrel preying upon a young chicken.[15] Wistrand reported seeing this same species eating a freshly killed snake.[16] 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;[17] Bradley, examining white-tailed antelope squirrels' stomachs, found at least 10% of his 609 specimens' stomachs contained some type of vertebrate, mostly lizards and rodents.[18] Morgart observed a white-tailed antelope squirrel capturing and eating a silky pocket mouse.[19]
Taxonomy[edit]
-
Grizzled giant squirrel (Ratufa macroura) of the Ratufinae
-
Southern flying squirrel (Glaucomys volans) of the Pteromyini
-
Prevost's squirrel (Callosciurus prevosti) of the Callosciurini
-
Unstriped ground squirrel (Xerus rutilus) of the Xerini
-
Alpine marmot (Marmota marmota) of the Marmotini
The living squirrels are divided into five subfamilies, with about 58 genera and some 285 species.[20] 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.[21]
A variety of fossil squirrels, from the latest Eocene to the Miocene, could not be assigned with certainty to any living lineage. At least some of these probably were variants of the oldest basal "protosquirrels" (in the sense that they lacked the full range of living squirrels' autapomorphies). The distribution and diversity of such ancient and ancestral forms suggest the squirrels as a group may have originated in North America.[22]
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 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 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.[22]
The main group of squirrels also can be split into three subgroups, which yield the remaining subfamilies. The Sciurinae contains the flying squirrels (Pteromyini) and the Sciurini, which among others contains the American tree squirrels; the former have often been considered a separate subfamily, but are now seen as a tribe of the Sciurinae. The pine squirrels (Tamiasciurus), on the other hand, are usually included with the main tree squirrel lineage, but appear to be about as distinct as the flying squirrels; hence, they are sometimes considered a distinct tribe, Tamiasciurini.[23]
Two of the three subfamilies are of about equal size, containing between nearly 70 and 80 species each; the third is about twice as large. The Sciurinae contains arboreal (tree-living) squirrels, mainly of the Americas and to a lesser extent Eurasia. The Callosciurinae is most diverse in tropical Asia and contains squirrels that are also arboreal, but have a markedly different habitus and appear more "elegant", an effect enhanced by their often very colorful fur. The Xerinae—the largest subfamily—are made up from the mainly terrestrial (ground-living) forms and include the large marmots and the popular prairie dogs, among others, as well as the tree squirrels of Africa; they tend to be more gregarious than other squirrels, which do not usually live together in close-knit groups.[22]
- Basal and incertae sedis Sciuridae (all fossil)
- 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)
See also[edit]
- American red squirrel
- Animal track
- Fox squirrel
- Purple squirrel
- Red squirrel
- Squirrel relationship with humans
- Western gray squirrel
Notes[edit]
- ^ Seebeck, J. H. "Sciuridae". Fauna of Australia. Retrieved 2013-11-24.
- ^ "squirrel, n.". The Oxford English Dictionary (2nd. ed.). Oxford University Press. 1989. Retrieved 8 November 2010.
- ^ Whitaker & Elman (1980): 370
- ^ "Squirrel". Online Etymology Dictionary. Retrieved 7 February 2008.
- ^ Tree Squirrels, Wildlife Online, 23 November 2010.
- ^ a b c Milton (1984)
- ^ Thorington, Richard W.; Koprowski, John L.; Steele, Michael A.; Whatton, James F. (2012). Squirrels of the World. Johns Hopkins University Press. p. 8. ISBN 1421404699.
- ^ a b Squirrel Place - squirrels.org - Retrieved 14 December 2010.
- ^ "Squirrel" - HowStuffWorks
- ^ Thorington, Richard W.; Koprowski, John L.; Steele, Michael A.; Whatton, James F. (2012). Squirrels of the World. Johns Hopkins University Press. p. 12. ISBN 1421404699.
- ^ "Red & Gray Squirrels in Massachusetts". MassWildlife. Massachusetts Division of Fisheries and Wildlife. Retrieved 3 April 2012.
- ^ Törmälä, Timo; Vuorinen, Hannu; Hokkanen, Heikki (1980). "Timing of circadian activity in the flying squirrel in central Finland". Acta Theriologica 25 (32–42): 461–474. doi:10.4098/at.arch.80-42. Retrieved 11 July 2007.
- ^ Richard W. Thorington, Katie Ferrell - Squirrels: the animal answer guide, JHU Press, 2006, ISBN 0-8018-8402-0, ISBN 978-0-8018-8402-3, p. 75.
- ^ Friggens, M. (2002). "Carnivory on Desert Cottontails by Texas Antelope Ground Squirrels". The Southwestern Naturalist 47 (1): 132–133. doi:10.2307/3672818. JSTOR 3672818.
- ^ Bailey, B. (1923). "Meat-eating propensities of some rodents of Minnesota". Journal of Mammalogy 4: 129.
- ^ Wistrand, E.H. (1972). "Predation on a Snake by Spermophilus tridecemlineatus". American Midland Naturalist 88 (2): 511–512. doi:10.2307/2424389. JSTOR 2424389.
- ^ Whitaker, J.O. (1972). "Food and external parasites of Spermophilus tridecemlineatus in Vigo County, Indiana". Journal of Mammalogy 53 (3): 644–648. doi:10.2307/1379067. JSTOR 1379067.
- ^ Bradley, W. G. (1968). "Food habits of the antelope ground squirrel in southern Nevada". Journal of Mammalogy 49 (1): 14–21. doi:10.2307/1377723. JSTOR 1377723.
- ^ Morgart, J. R. (May 1985). "Carnivorous behavior by a white-tailed antelope ground squirrel Ammospermophilus leucurus". The Southwestern Naturalist 30 (2): 304–305. doi:10.2307/3670745. JSTOR 3670745.
- ^ Wilson, D.E.; Reeder, D.M. (2011). "Class Mammalia Linnaeus, 1758. In: Zhang, Z.-Q. (Ed.) Animal biodiversity: An outline of higher-level classification and survey of taxonomic richness". Zootaxa 3148: 56–60.
- ^ Emry, R. J.; Korth, W. W. (2007). "A new genus of squirrel (Rodentia, Sciuridae) from the mid-Cenozoic of North America". Journal of Vertebrate Paleontology 27 (3): 693. doi:10.1671/0272-4634(2007)27[693:ANGOSR]2.0.CO;2.
- ^ a b c Steppan & Hamm (2006)
- ^ Steppan et al. (2004), Steppan & Hamm (2006)
References[edit]
- 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. & Hamm, Shawn M. (2006): Tree of Life Web Project – Sciuridae (Squirrels). Version of 13 May 2006. Retrieved 10 December 2007.
- Steppan, S. J.; Storz, B. L.; 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 (3): 703–719. doi:10.1016/S1055-7903(03)00204-5. PMID 15012949.
- Thorington, R.W. & Hoffmann, R.S. (2005): Family Sciuridae. In: Mammal Species of the World – A Taxonomic and Geographic Reference: 754–818. Johns Hopkins University Press, Baltimore.
- Whitaker, John O. Jr. & Elman, Robert (1980): The Audubon Society Field Guide to North American Mammals (2nd ed.). Alfred Knopf, New York. ISBN 0-394-50762-2
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Squirrels are important sources of prey for a vast array of predators including predators that are threatened or endangered. For rare species such as snow leopards and northern spotted owls, squirrels are an essential part of the diet. Black-footed ferrets eat almost exclusively prairie dogs. Tree and flying squirrels are also essential in the regeneration of forests around the world through their seed dispersal activities. This is not only because seeds are left in the feces of these animals but also because of the caching habits of many squirrels. Squirrels are also important in dispersing the spores of fungi that they eat, including ecologically important underground endorhyzal fungi. Squirrels serve as host to a number of parasites such as fleas, mites and ticks. These parasites are known for causing the transfer of a number of diseases, such as plague, from squirrel to squirrel and to other mammals, including humans. Some species have also been identified as playing the role of a keystone species in their ecosystem. One study conducted by Kotiliar et al. (1999) confirmed that prairie dogs acted as a keystone species in the Great Plains of the United states. Not only were prairie dogs an important food source for predators such as golden eagles and swift foxes, but their burrows were very important for a number of animals as well. Abandoned burrows were used as housing for animals ranging from raccoons and cottontail rabbits to shrews and voles. Others were found to feed on the vegetation that had been disturbed by the construction of prairie dog colonies. The digging of these burrows were also found to be beneficial for a number of plants because of the aeration of soil and fertilizing properties in their feces.
Ecosystem Impact: disperses seeds; pollinates; soil aeration ; keystone species
Commensal/Parasitic Species:
- mites and ticks
- fleas
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Sciurids are a typical meal for many opportunistic domestic and wild predators. The most common predators may be birds of prey, such as eagles and hawks, falcons, owls, and cats, canids, and weasels. But many predators have been observed eating squirrels, including large snakes, bigmouth bass, and chimpanzees . Squirrels are also hunted for food and fur by humans.
The most common tactics of sciurids for avoiding predators is camouflage and escape. Squirrels typically have coats with color that matches their surroundings. Tree squirrels often have lighter coloration on the ventral side compared to the dorsal, allowing them to blend in with the light sky to a predator that is looking at the squirrel from below and at to blend in with the dark ground when being stalked by an aerial predator. Squirrels also avoid capture by quickly darting away from predators, remaining vigilant, biting, clawing, hiding in burrows or nests and sounding alarm calls. Squirrels that are commonly attacked by snakes take on a completely different defense tactic known as mobbing. Especially common in communal prairie dogs (Cynomys), these squirrels will attack snakes, pouncing, biting and scratching until the snake leaves the area near the burrow or is killed.
Known Predators:
- birds of prey (Accipitridae)
- cats (Felidae)
- foxes (Vulpes)
- owls (Strigiformes)
- snakes (Serpentes)
- martens (Martes)
- bears (Ursidae)
- African wild dogs (Lycaon pictus)
- coyotes (Canis latrans)
- badgers (Taxidea taxus)
- weasels and ferrets (Mustela)
- great herons (Ardea)
- raccoons (Procyon lotor)
- crows and ravens (Corvus)
- chimpanzees (Pan troglodytes)
- domestic dogs (Canis lupus familiaris)
- domestic Cats (Felis catus)
- ermine (Mustela erminea)
- wolves (Canis lupus)
- humans (Homo sapiens)
- wolverines (Gulo gulo)
- snow leopards (Uncia uncia)
- wild cats (Felis silvestris)
- bigmouth bass (Micropterus salmoides)
Anti-predator Adaptations: cryptic
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Animal / dung saprobe
sporangiophore of Pilaira anomala is saprobic in/on dung or excretions of dung of Sciuridae
Animal / dung saprobe
sporangiophore of Pilobolus crystallinus var. crystallinus is saprobic in/on dung or excretions of dung of Sciuridae
Animal / dung saprobe
sporangiophore of Pilobolus crystallinus var. kleinii is saprobic in/on dung or excretions of dung of Sciuridae
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Sciuridae is prey of:
fox
Strigiformes
Mustelinae
Stercorarius
Based on studies in:
USA: Alaska (Tundra)
This list may not be complete but is based on published studies.
- J. Brown, Ecological investigations of the Tundra biome in the Prudhoe Bay Region, Alaska, Special Report, no. 2, Biol. Pap. Univ. Alaska (1975), from p. xiv.
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Source | http://spire.umbc.edu/fwc/ |
Sciuridae preys on:
willows
sedges
grasses
Colaptes auratus
Reithrodontomys megalotis
Ictinia mississippiensis
Based on studies in:
USA: Alaska (Tundra)
This list may not be complete but is based on published studies.
- J. Brown, Ecological investigations of the Tundra biome in the Prudhoe Bay Region, Alaska, Special Report, no. 2, Biol. Pap. Univ. Alaska (1975), from p. xiv.
- Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006. The Animal Diversity Web (online). Accessed February 16, 2011 at http://animaldiversity.org. http://www.animaldiversity.org
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Squirrels have distinct vocalizations for particular situations, such as infants calling to their mothers and adults vocalizing during aggression. Males vocalize during the mating season to attract mates. Many squirrel species use distinctive alarm calls to warn conspecifics of dangers, including alarm calls that warn of specific threats, distinguishing between aerial and terrestrial predators. Squirrels also use posture and movement as a form of communication, with messages carried by tail position, stomping of the feet, or body posture. As in most mammals, olfaction is very important in communication. Females indicate sexual receptiveness through pheromones and social position or relatedness may also be inferred through chemical cues.
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: pheromones ; scent marks
Perception Channels: visual ; tactile ; acoustic ; chemical
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Squirrels have been found to live a maximum of 8 to 14 years in the wild and up to 16 or more years in captivity. However, many squirrels do not live past their first year of life in the wild.
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