Древесные белки: описание и особенности поведения.

Small tree dwelling mammals that are members of the squirrel family (Sciuridae)

Tree squirrels are the members of the squirrel family (Sciuridae) commonly just referred to as "squirrels". They include more than 100 arboreal species native to all continents except Antarctica and Oceania. They do not form a single natural, or monophyletic, group; they are variously related to others in the squirrel family, including ground squirrels, flying squirrels, marmots, and chipmunks. The defining characteristic used to determine which species of Sciuridae are tree squirrels is dependent on their habitat rather than their physiology. Tree squirrels live mostly among trees, as opposed to those that live in burrows in the ground or among rocks. An exception is the flying squirrel that also makes its home in trees, but has a physiological distinction separating it from its tree squirrel cousins: special flaps of skin called patagia, acting as glider wings, which allow gliding flight. The best known genus of tree squirrels is Sciurus, which includes the eastern gray squirrel of North America (introduced to Great Britain in the 1870s), the red squirrel of Eurasia, and the North American fox squirrel, among many others. Many tree squirrel species have adapted to human altered environments such as rural farms, suburban backyards and urban parks.

Squirrels are sometimes considered pests because of their propensity to chew on various edible and inedible objects, and their stubborn persistence in trying to get what they want. Their characteristic gnawing trait also aids in maintaining sharp teeth, and because their teeth grow continuously, prevents their over growth. On occasion, squirrels will chew through plastic and even metal to get to the food. Tree squirrels may bury food in the ground for later retrieval. Squirrels use their keen sense of smell to search for buried food, but can dig numerous holes in the process. This may become an annoyance to gardeners with strict landscape requirements, especially when the garden contains edibles. Homeowners in areas with a heavy squirrel population must be vigilant in keeping attics, basements, and sheds carefully sealed to prevent property damage caused by nesting squirrels. A squirrel nest is called a "drey". Squirrels are a serious fire hazard when they break into buildings. They often treat exposed power cables as tree branches, and gnaw on the electrical insulation. The resulting exposed conductors can short out, causing a fire. For this reason alone, squirrel nests inside buildings cannot be safely ignored. A squirrel nest will also cause problems with noise, excreta, unpleasant odors, and eventual structural damage. Capsaicin and Ro pel are other forms of repellent. Effective baits include fruit, peanut butter, nuts, seeds and vanilla extract. An alternative method is to wait until squirrels have left in search of food, and then close up all their access openings, or to install one way trap doors or a carefully angled pipe. Squirrels are often the cause of power outages. They can readily climb a power pole and crawl or run along a power cable. The animals will climb onto power transformers or capacitors looking for food, or a place to cache acorns. If they touch a high voltage conductor and a grounded portion of the enclosure at the same time, they are electrocuted, and often 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, squirrels will often chew on tree branches or even the occasional live power line. Squirrels otherwise appear to be safe and pose almost zero risk of transmitting rabies. Squirrels cause economic losses to homeowners, nut growers, and 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.

In regions where squirrels are plentiful, tire flattened roadkill is a common sight on roadways, especially in the spring and fall, when there is a fresh crop of young rodents. Motorists have caused serious accidents by attempting to swerve or stop to avoid a squirrel in the road. Evasive maneuvers are difficult since squirrels are much more agile and have much quicker reaction times than motorists in heavy vehicles; the majority of vehicular encounters end with no harm to either party. An effort to mitigate these hazards to both squirrels and humans is the Nutty Narrows Bridge in Longview, Washington, listed on the National Register of Historic Places. It provides a way for squirrels to cross a busy street safely.

Tree squirrels are a common type of urban wildlife. They can be trained to be hand fed, and will take as much food as is available because they cache the surplus. Squirrels living in parks and campuses in cities have learned that humans are typically a ready source of food, either deliberately or from careless disposal of surplus. Some people do "squirrel fishing" as a way of simultaneously playing with and feeding squirrels. Humans commonly offer various nuts and seeds; 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 sometimes hunted as game animals, whether for their fur or as food. In the Middle Ages the red squirrel was hunted for its blue gray winter coat, traditionally called vair, which now lends its name to a heraldic fur. The hairs from squirrel tails are prized in fly fishing when tying fishing flies.

In many areas of the US, squirrels are still hunted for food, as they were historically. Recipes calling for squirrel even appear in cookbooks, including James Beard's American Cookery and pre 1997 copies of The Joy of Cooking. Other similar stews were also based on squirrel meat, including burgoo and Southern Illinois chowder. Although squirrel meat is low in fat content, unlike most game meat it has been found by the American Heart Association to be high in cholesterol. Squirrels Unlimited host a World Championship Squirrel cook off each year in Bentonville, Arkansas.

For most of the history of the United Kingdom, squirrel has been a meat not commonly eaten, and even scorned by many. In the early 21st century however, the wild squirrel has become a more popular meat to cook with, Specifically, Britons are cooking with the invasive gray squirrel, which is praised for its low fat content and the fact that it comes from free range sources. Toxic waste had been illegally dumped at this location for many years, before authorities cracked down on this practice in the 1980s. In 1997, doctors in Kentucky published a paper in the Lancet that considered a possible association between the local tradition of consuming squirrel brains and five cases of Creutzfeldt–Jakob disease, a rare but serious prion based disorder. The authors posed this as a mere possibility, unconfirmed by either post mortem analysis of the patients' brain tissue, or identification of a contagious prion agent in squirrels. Nonetheless, the Lancet article generated substantial media coverage, including articles in the New Yorker and New York Times. A 2015 case of CJD in a Pittsburgh man who had eaten squirrel brains played out similarly: the media seized on the patient's unconventional food choice, positing squirrel brains as the source of his disease. The doctor who made the initial report later clarified that he had not meant to assert the squirrel meat was the cause. Analysis of the patient's brain tissue ruled out the possibility of CJD acquired from food. As of 2018, Creutzfeldt–Jakob disease had never been identified in squirrels, and the association between squirrel consumption and CJD remained speculative.

The biggest source of food for tree squirrels is tree nuts. Red squirrels store nuts in a single stash (a midden) that tends to dry out, so the seeds don't take root. Fox squirrels and gray squirrels bury nuts over a widespread area (scatterhoarding), and often forget them, resulting in new trees (mutualism).

[[File:AM 738 4to Ratatoskr. png|thumb|upright|Seventeenth century Icelandic manuscript illustration depiction Ratatoskr, a squirrel in Norse mythology said to live in the world tree Yggdrasil and to convey insults and gossip Rama rewards the squirrel by stroking his back with his three middle fingers, thus giving the Indian palm squirrel the three white stripes that appear on its back. According to Richard W. Thorington, Jr. and Katie E. Ferrell, this legend may have originated from the red squirrel's habit of giving a "scolding alarm call in response to danger", which some Norsemen may have imagined as insults. An episode of the radio program This American Life called "Squirrel Cop" describes the unintentionally humorous misadventure of a newly hired policeman in trying to remove a frantic squirrel from a homeowner's living room, which results in personal injury and a small fire. First aired in 1998, this episode turned out to be one of the most popular ones of the series, prompting rebroadcasts and a lead position on the two CD compilation Crimebusters + Crossed Wires: Stories from This American Life.

One of the ways that squirrels affect human society is inspired by the fascination that people seem to have over local populations of white squirrels (often misidentified as being albino). This manifests itself by the creation of social group communities that form from a commonly shared interest in these rare animals. 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. 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. A project run by Untamed Science is seeking to report and document the occurrence of both white squirrels, albinos, and other piebald morphs. Users are encouraged to submit their sightings.

thumb|right|Welcome sign for Kenton, Tennessee, an example of competition for "White Squirrel Capital". 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". A list of white squirrel sightings around the world is maintained by the White Squirrel Research Institute, a group based in Brevard, North Carolina. Other towns that have reported white squirrel populations in North America (although not necessarily competing to be the "official" white squirrel capital) include Bowling Green, Kentucky; Columbia, Mississippi; DeForest, Wisconsin; Stratford, Connecticut; and some of the snowbelt cities in the Western, Central and Finger Lakes regions of New York State (Buffalo, Rochester, Ithaca and Syracuse). neighborhood of Toronto, Ontario is locally known for white squirrel sightings.

thumb|right|Red squirrel at a feeding tray in the Lake District, England. A decline of the red squirrel and the rise of the eastern gray squirrel, an introduced species from North America, has been widely remarked upon in British popular culture. It is mostly regarded as the invading greys driving out the native red species. Evidence also shows that grey squirrels are vectors of the squirrel parapoxvirus for which no vaccine is currently available, and which is deadly to red squirrels but does not seem to affect the non native host. Currently, the red squirrel's range has been reduced to the coniferous forests in Scotland, and in England's Formby, the Lake District, Brownsea Island, and the Isle of Wight. The majority of England's red squirrels are found in the county of Northumberland. Special measures are in place to contain and remove any infiltration of grey squirrels into these areas. Though the population has dramatically decreased, they remain listed on the IUCN Red List as Least Concern. As of 2008, the eastern gray squirrel was regarded as vermin and it was illegal to release any into the wild; any caught could be released only if one applied for and was granted a licence to do so. As of 2015, any caught in Scotland had to be humanely killed.