That word "squirrel", first attested in 1327, comes from the Anglo-Normanesquirel which is from the Old Frenchescurel, 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, cognates of which are still used in other Germanic languages, including the GermanEichhörnchen (diminutive of Eichhorn, which is not as frequently used), the Norwegianikorn/ekorn, the Dutcheekhoorn, the Swedishekorre and the Danishegern.
Characteristics
Reaching out for food on a garden bird feeder, this squirrel can rotate its hind feet, allowing it to descend a tree head-first.
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 Laotian giant flying squirrelat 1.08 m (3 ft 7 in) in length and the Alpine marmot, which 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.[10]
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.[11]
Some causes of premature death include nests which have fallen out of trees, of which the mother will leave the young if the body temperature is not correct. Many squirrels have been rescued by people prompting fostering of baby squirrels or wildlife rehabilitators before turning them back into the wild. [12]
Behavior
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,[13] while flying squirrels tend to be nocturnal—except for lactating flying squirrels and their offspring, which have a period of diurnality during the summer.[14]
Feeding
Squirrel eating a fruit in Manyara National Park, Tanzania
Squirrel eating a peanut.
Squirrel from the jungle of Alwar, Rajasthan
Squirrel eating grains
A domestic squirrel.
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.[15]
Predatory behavior has been noted by various species of ground squirrels, in particular the thirteen-lined ground squirrel.[16] For example, Bailey, a scientist in the 1920s, observed a thirteen-lined ground squirrel preying upon a young chicken.[17] Wistrand reported seeing this same species eating a freshly killed snake.[18] 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;[19] 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.[20] Morgart observed a white-tailed antelope squirrel capturing and eating a silky pocket mouse.[21]
The living squirrels are divided into five subfamilies, with about 58 genera and some 285 species.[22] 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.[23]
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.[24]
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.[24]
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.[25]
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.[24]
Squirrels are nimble, bushy-tailed rodents found all over the world. They belong to the Sciuridae family, which includes prairie dogs, chipmunks and marmots.
There are more than 200 species of squirrels, according to the Integrated Taxonomic Information System (ITIS), and they are categorized into three types: tree squirrels, ground squirrels and flying squirrels. These three categories are further broken down into many squirrel types, such as Albino, Mountain Tree, Antelope, Spotted, Grey, American Red, Douglas, Fox, Pygmy, Northern Flying, Southern, Arizona Gray, Idaho, Arctic Ground, Albert’s, Franklin, Richardson, Rock, White and Black squirrel.
Size
Since there are so many types of squirrels, they range greatly in size. The smallest squirrel is the African pygmy squirrel. It grows to 2.8 to 5 inches (7 to 13 centimeters) in length and weighs just 0.35 ounces (10 grams). The Indian giant squirrel is the world's largest known squirrel. It grows to 36 inches (1 meter) long and weighs up to 4 pounds (1.8 kilograms).
American red squirrels feed on the seeds of evergreen trees.
Credit: Barb Thomas
Grey squirrels, commonly found in North America, are medium-size squirrels. They grow to 15 to 20 inches (38.1 to 50.8 cm) in length, with their tails adding an extra 6 to 9.5 inches (15.24 to 24.13 cm) to their length. They typically weigh about 1 to 1.5 pounds (0.45 to 0.68 kg).
A group of squirrels are called a scurry or dray. They are very territorial and will fight to the death to defend their area. Mother squirrels are the most vicious when defending their babies.
Some squirrels are crepuscular. This means that they are only active at dawn and dusk.
Where do squirrels live?
Squirrels live on every continent except in Australia and Antarctica, according to the BBC.
Tree squirrels typically live in wooded areas, since they prefer to live in trees. Ground squirrels live up to their names. They dig burrows, a system of tunnels underground, to live in. Some squirrels also hibernate in burrows during the winter to keep warm.
Albino squirrels are quite popular in some parts of the United States. Olney, Ill., is one of the towns that calls itself "Home of the White Squirrels," along with Marionville, Mo., and Brevard, N.C. The township of Kenton, Tenn., proudly boasts a population of 200 of the furry, pale rodents.
Credit: Andrea Browning
Flying squirrels make their homes in tree holes or nests that are built into the crooks of branches. To get from tree to tree or from a tree to the ground, flying squirrels spread the muscle membrane between their legs and body and glide on the air. They can glide up to 160 feet (48 m), making it look like they can fly.
On average, squirrels eat about one pound of food per week. Many people think that squirrels only eat nuts, but this isn't true. Squirrels are omnivores, which means they like to eat plants and meat. Squirrels mainly eat fungi, seeds, nuts and fruits, but they will also munch on eggs, small insects, caterpillars, small animals and even young snakes.
What do squirrels eat?
To prepare for cold months, squirrels will bury their food. In the winter months they have a store of food they can eat when supplies are scarce.
Baby squirrels
A female carries her young for a gestation period of 29 to 65 days, depending on the size of the species; smaller squirrels have shorter gestation periods, according to the University of Michigan's Animal Diversity Web. Mothers give birth to two to eight offspring at one time. Babies are called kits or kittens and are born blind. They depend on their mothers for around two or three months.
A boost of stress during pregnancy helps red squirrels ensure that their pups will grow fast.
Credit: Photo by Ryan W. Taylor
After seven to eight weeks, the young are weaned. When the kits leave the nest, they don't travel farther than 2 miles from home, according to the Massachusetts Department of Wildlife and Fisheries. Some species of squirrel have new litters every few months or as little as twice per year.
Subfamilies: Callosciurinae (Southern Asian tree squirrels), Ratufinae (giant tree squirrels), Sciurillinae (South American pygmy squirrels), Sciurinae (includes flying squirrels), Xerinae (includes ground squirrels)
Genera & species: 21 genera & more than 200 species, including Lariscus hosei (Four-striped ground squirrel), Exilisciuruswhiteheadi (Tufted pygmy squirrel), Ratufabicolor (Black giant squirrel), Glaucomyssabrinusi (Northern flying squirrel) and Tamiasciurushudsonicus (Red squirrel)
Conservation status
According to the International Union for the Conservation of Nature's Red List, these species are endangered: San Joaquin antelope ground squirrel, woolly flying squirrel, Sipora flying squirrel, Mentawi flying squirrel, Siberut flying squirrel, smoky flying squirrel, Vincent's bush squirrel, Baja California rock squirrel, Idaho ground squirrel, Perote ground squirrel, fraternal squirrel and Mearns' squirrel. The Namdapha flying squirrel is critically endangered.
Other facts
Squirrels have four teeth in the front of their mouth that constantly grow throughout their lives. This ensures that their teeth don't wear down to nubs from gnawing on nuts and other objects.
These rodents have remarkable little bodies. For example, a squirrel has padded feet that cushions jumps from up to 20 feet (6 meters) long. Their eyes are high on their head and placed on each side of the head so they can see a large amount of their surroundings without having to turn their head. They are also fantastic runners. Squirrels can run 20 mph (32 kph).
The gray squirrel (Sciuruscarolinensis) isn't just gray. It comes in a variety of colors, such as white, gray, brown and black. These little squirrels are great at planting trees. They bury their acorns, but forget where they put them. The forgotten acorns become oak trees.
Correction: This article was updated on May 4, 2016, to reflect the correct length of the gestation period.
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