Hubbry Logo
search
logo
Eastern gray squirrel avatar
Eastern gray squirrel
Eastern gray squirrel
current hub
2208527

Eastern gray squirrel

logo
Community Hub0 Subscribers
Read side by side
Eastern gray squirrel
View on Wikipedia
from Wikipedia

Eastern gray squirrel[1]
Temporal range:
Late Pleistocene – present (18,735–0 YBP)[2]
Calls recorded in Surrey, England

Secure  (NatureServe)[4]
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Sciuridae
Genus: Sciurus
Subgenus: Sciurus
Species:
S. carolinensis
Binomial name
Sciurus carolinensis
Gmelin, 1788
Subspecies
  • S. c. carolinensis
  • S. c. extimus
  • S. c. fuliginosus
  • S. c. hypophaeus
  • S. c. pennsylvanicus
Native range in red
Synonyms
  • Neosciurus carolinensis[5]
  • S. pennsylvanica
  • S. hiemalis
  • S. leucotis
  • S. fulginosus
  • S. migratorius

The eastern gray squirrel (Sciurus carolinensis), also known, outside of the United States, as the grey squirrel, is a species of tree squirrel in the genus Sciurus. It is native to eastern North America, where it is the most prodigious and ecologically essential natural forest regenerator.[6][7] Widely introduced to certain places around the world, the eastern gray squirrel in Europe, in particular, is regarded as an invasive species.

In Europe, Sciurus carolinensis is included (since 2016) in the list of Invasive Alien Species of Union concern (the Union list).[8] This implies that this species cannot be imported, bred, transported, commercialized, or intentionally released into the environment in the whole of the European Union.[9]

Distribution

[edit]

Sciurus carolinensis is native to the eastern and midwestern United States, and to the southerly portions of the central provinces of Canada. In the mid-1800s the population in the midwestern United States was described as being "truly astonishing," but human predation and habitat destruction through deforestation resulted in drastic population reductions, to the point that the animal was almost absent from Illinois by 1900.[10]

The native range of the eastern gray squirrel overlaps with that of the fox squirrel (Sciurus niger), with which it is sometimes confused, although the core of the fox squirrel's range is slightly more to the west. The eastern gray squirrel is found from New Brunswick, through southwestern Quebec and throughout southern Ontario plus in southern Manitoba, south to East Texas and Florida.[3] Breeding eastern gray squirrels are found in Nova Scotia, but whether this population was introduced or came from natural range expansion is not known.[11]

A prolific and adaptable species, the eastern gray squirrel has also been introduced to, and thrives in, several regions of the western United States and in 1966, this squirrel was introduced onto Vancouver Island in Western Canada in the area of Metchosin, and has spread widely from there. They are considered highly invasive and a threat to both the local ecosystem and the native squirrel, the American red squirrel.[12]

Overseas, eastern gray squirrels in Europe are a concern because they have displaced some of the native squirrels there. They have been introduced into Ireland,[13] Britain, Italy, South Africa, and Australia (where it was extirpated by 1973).[3]

In Ireland, the native squirrel – also colored red – the Eurasian red squirrel S. vulgaris – has been displaced in several eastern counties, though it still remains common in the south and west of the country.[14][page needed] The gray squirrel is also an invasive species in Britain; it has spread across the country and has largely displaced the red squirrel.[15] That such a displacement might happen in Italy is of concern, as gray squirrels might spread to other parts of mainland Europe.[15][16]

Brown morph, in Ontario

Fossil record

[edit]

S. carolinensis is known to have occurred at least 18 times throughout the North American Pleistocene fossil record, across eight different US states,[note 1] with some fossils allegedly dating back as early as the late Irvingtonian period.[17] Body size seems to have increased during the early to middle Holocene and then decreased to the present size seen today.[18]

A single fossil specimen (held and cataloged by South Carolina State Museum's natural history collection as SC93.105.172–.174) is known from the Ardis local fauna site in Harleyville, South Carolina.[2] This specimen consists of a partial humerus (.172) and two partial tibiae (.173, .174), which are anatomically indistinguishable from that of contemporary S. carolinensis.[2] Surrounding fossil material from the site has been dated back to 18,940–18,530 years ago, during the Late Pleistocene (late Rancholabrean) epoch, and indicates that the site was likely a hardwood-conifer swamp during this time.[2]

Etymology

[edit]

The generic name, Sciurus, is derived from two Greek words, skia 'shadow' and oura 'tail'. This name alludes to the squirrel sitting in the shadow of its tail.[19] The specific epithet, carolinensis, refers to the Carolinas, where the species was first recorded and where the animal is still extremely common. In the United Kingdom and Canada, it is simply referred to as the "grey squirrel". In the US, "eastern" is used to differentiate the species from the western gray squirrel (Sciurus griseus).

Characteristics

[edit]
Bounding tracks in concrete

The eastern gray squirrel has predominantly gray fur, but it can have a brownish color. It has a usual white underside as compared to the typical brownish-orange underside of the fox squirrel.[20] It has a large bushy tail. Particularly in urban situations where the risk of predation is reduced, both white-colored[21] and black-colored individuals are quite often found. The melanistic form, which is almost entirely black, is predominant in certain populations and in certain geographic areas, such as in large parts of southeastern Canada. Melanistic squirrels appear to exhibit a higher cold tolerance than the common gray morph; when exposed to −10 °C, black squirrels showed an 18% reduction in heat loss, a 20% reduction in basal metabolic rate, and an 11% increase to non-shivering thermogenesis capacity when compared to the common gray morph.[18] The black coloration is caused by an incomplete dominant mutation of MC1R, where E+/E+ is a wild type squirrel, E+/EB is brown-black, and EB/EB is black.[22]

The head and body length is from 23 to 30 cm (9.1 to 11.8 in), the tail from 19 to 25 cm (7.5 to 9.8 in), and the adult weight varies between 400 and 600 g (14 and 21 oz).[23][24] They do not display sexual dimorphism, meaning there is no gender difference in size or coloration.[25]

The tracks of an eastern gray squirrel are difficult to distinguish from the related fox squirrel and Abert's squirrel, though the latter's range is almost entirely different from the gray's. Like all squirrels, the eastern gray shows four toes on the front feet and five on the hind feet. The hind foot-pad is often not visible in the track. When bounding or moving at speed, the front foot tracks will be behind the hind foot tracks. The bounding stride can be two to three feet long.[26]

The dental formula of the eastern gray squirrel is 1023/1013 (upper teeth/lower teeth).[18]

1.0.2.31.0.1.3 × 2 = 22 total teeth.

Incisors exhibit indeterminate growth, meaning they grow consistently throughout life (as is true for all rodents), and their cheek teeth exhibit brachydont (low-crowned teeth) and bunodont (having tubercles on crowns) structures.[18]

Colour mutations
Melanistic
Leucistic
Albino

Growth and ontogeny

[edit]
Newborn gray squirrel developing fur. They are born hairless and blind.

Newborn squirrels are called kits, kittens,[27] or pups.[28][29] They weigh 13–18 grams at birth. They are born blind, entirely hairless, and pink with vibrissae present at birth. 7–10 days postpartum, the skin begins to darken, just before the juvenile pelage grows in. Lower incisors erupt 19–21 days postpartum, while upper incisors erupt after 4 weeks. Cheek teeth erupt during week 6. Eyes open after 21–42 days, and ears open 3–4 weeks postpartum. Weaning is initiated around 7 weeks postpartum, and is usually finished by week 10, followed by the loss of the juvenile pelage. Full adult body mass is achieved by 8–9 months after birth.[18]

Diseases

[edit]

Diseases such as typhus, plague, and tularemia are spread by eastern gray squirrels. If not properly treated, these diseases have the potential to kill squirrels. When bitten or exposed to bodily fluids, humans can contract these diseases. Eastern gray squirrels may also carry parasites such as ringworm, fleas, lice, mites, and ticks which can kill their squirrel host. Their skin may become rough, blotchy, and prone to hair loss due to the mite parasite during the chilly winter months. The parasites are not transferred to people when these squirrels reside in attics or homes.[30] A frequent illness spread by ticks is Lyme disease.[31] Ticks can also spread Rocky Mountain spotted fever. It can result in damage to internal organs including the heart and kidney if not properly treated.[32] An eastern gray squirrel is susceptible to diseases including fibromatosis and squirrelpox. A squirrel with fibromatosis, a virus-induced illness, may grow massive skin tumors all over the body. Blindness could result from a tumor that is located close to a squirrel's eye.[33]

Behavior and ecology

[edit]
Reaching out for food on a garden bird feeder, this squirrel can rotate its hind feet, allowing it to descend a tree head-first.

Like many members of the family Sciuridae, the eastern gray squirrel is a scatter-hoarder; it hoards food in numerous small caches for later recovery.[3] Some caches are quite temporary, especially those made near the site of a sudden abundance of food which can be retrieved within hours or days for reburial in a more secure site. Others are more permanent and are not retrieved until months later. Each squirrel is estimated to make several thousand caches each season. The squirrels have very accurate spatial memory for the locations of these caches, using distant and nearby landmarks to retrieve them. Smell is used partly to uncover food caches, and also to find food in other squirrels' caches. Scent can be unreliable when the ground is too dry or covered in snow.[34]

Squirrels sometimes use deceptive behavior to prevent other animals from retrieving cached food. For example, they will pretend to bury the object if they feel that they are being watched. They do this by preparing the spot as usual, for instance, digging a hole or widening a crack, miming the placement of the food, while actually concealing it in their mouths, and then covering up the "cache" as if they had deposited the object. They also hide behind vegetation while burying food or hide it high up in trees (if their rival is not arboreal). Such a complex repertoire suggests that the behaviours are not innate, and imply theory of mind thinking.[35][36]

The eastern gray squirrel is one of very few mammalian species that can descend a tree head-first. It does this by turning its feet so the claws of its hind paws are backward-pointing and can grip the tree bark.[37][38]

A gray squirrel in a drey located in a window.

Eastern gray squirrels build a type of nest, known as a drey, in the forks of trees, consisting mainly of dry leaves and twigs. The dreys are roughly spherical, about 30 to 60 cm in diameter and are usually insulated with moss, thistledown, dried grass, and feathers to reduce heat loss.[25] Males and females may share the same nest for short times during the breeding season, and during cold winter spells. Squirrels may share a drey to stay warm. They may also nest in the attic or exterior walls of a house, where they may be regarded as pests, as well as fire hazards due to their habit of gnawing on electrical cables.[39] In addition, squirrels may inhabit a permanent tree den hollowed out in the trunk or a large branch of a tree.[40]

Eastern gray squirrels exhibit diurnal or crepuscular behavior depending on the season,[24] and tend to avoid the heat in the middle of a summer day.[40] They do not hibernate.[41]

Reproduction

[edit]

Eastern gray squirrels can breed twice a year, but younger and less experienced mothers normally have a single litter per year in the spring. Depending on forage availability, older and more experienced females may breed again in summer.[42] In a year of abundant food, 36% of females bear two litters, but none will do so in a year of poor food.[18] Their breeding seasons are December to February and May to June, though this is slightly delayed in more northern latitudes.[24][40] The first litter is born in February or March, the second in June or July, though, again, bearing may be advanced or delayed by a few weeks depending on climate, temperature, and forage availability. In any given breeding season, an average of 61 – 66% of females bear young.[18] If a female fails to conceive or loses her young to unusually cold weather or predation, she re-enters estrus and has a later litter. Five days before a female enters estrus, she may attract up to 34 males from up to 500 meters away. Eastern gray squirrels exhibit a form of polyandry, in which the competing males will form a hierarchy of dominance, and the female will mate with multiple males depending on the hierarchy established.[18]

Eastern gray squirrel drey

Normally, one to four young are born in each litter, but the largest possible litter size is eight.[18] The gestation period is about 44 days.[18] The young are weaned around 10 weeks, though some may wean up to six weeks later in the wild. They begin to leave the nest after 12 weeks, with autumn born young often wintering with their mother. Only one in four squirrel kits survives to one year of age, with mortality around 55% for the following year. Mortality rates then decrease to around 30% for following years until they increase sharply at eight years of age.[18]

Rarely, eastern gray females can enter estrus as early as five and a half months old,[40] but females are not normally fertile until at least one year of age. Their mean age of first estrus is 1.25 years.[18] The presence of a fertile male will induce ovulation in a female going through estrus.[18] Male eastern grays are sexually mature between one and two years of age.[43] Reproductive longevity for females appears to be over 8 years, with 12.5 years documented in North Carolina.[18] These squirrels can live to be 20 years old in captivity, but in the wild live much shorter lives due to predation and the challenges of their habitat. At birth, their life expectancy is 1–2 years; an adult typically can live to be six, with exceptional individuals making it to 12 years.

Communication

[edit]
Calls recorded in Surrey, England

As in most other mammals, communication among eastern gray squirrel individuals involves both vocalizations and posturing. The species has a quite varied repertoire of vocalizations, including a squeak similar to that of a mouse, a low-pitched noise, a chatter, and a raspy "mehr mehr mehr". Other methods of communication include tail-flicking and other gestures, including facial expressions. Tail flicking and the "kuk" or "quaa" call are used to ward off and warn other squirrels about predators, as well as to announce when a predator is leaving the area.[44] Squirrels also make an affectionate coo-purring sound that biologists call the "muk-muk" sound. This is used as a contact sound between a mother and her kits and in adulthood, by the male when he courts the female during mating season.[44] The use of vocal and visual communication has been shown to vary by location, based on elements such as noise pollution and the amount of open space. For instance, populations living in large cities generally rely more on the visual signals, due to the generally louder environment with more areas without much visual restriction. However, in heavily wooded areas, vocal signals are used more often due to the relatively lower noise levels and a dense canopy restricting visual range.[45]

Habitat

[edit]
Eastern gray squirrel staying in a birdhouse

In the wild, eastern gray squirrels can be found inhabiting large areas of mature, dense woodland ecosystems, generally covering 100 acres (40 hectares) of land.[40] These forests usually contain large mast-producing trees such as oaks and hickories, providing ample food sources. Oak-hickory hardwood forests are generally preferred over coniferous forests due to the greater abundance of mast forage.[24] This is why they are found only in parts of eastern Canada which do not contain boreal forest (i.e. they are found in some parts of New Brunswick, in southwestern Quebec, throughout southern Ontario and in southern Manitoba).[ambiguous]

Eastern gray squirrels generally prefer constructing their dens upon large tree branches and within the hollow trunks of trees. They also have been known to take shelter within abandoned bird nests. The dens are usually lined with moss plants, thistledown, dried grass, and feathers. These perhaps provide and assist in the insulation of the den, used to reduce heat loss. A cover to the den is usually built afterwards.[46] Eastern gray squirrels also use dens for protection from predators and to help them look after their young. Young survive 40 percent less if they lived in a leaf nest compared to a den. Squirrels tend to claim 2-3 dens at the same time. Canopy and midstory trees are used by squirrels to hide from predators such as hawks and owls. The typical squirrel ranges over 1.5 to 8 acres (0.61 to 3.24 ha) and tends to be smaller where more of them are found.[47]

Close to human settlements, eastern gray squirrels are found in parks and back yards of houses within urban environments and in the farmlands of rural environments.[48]

Ecosystem

[edit]

Eastern gray squirrels forage tree seeds and disperse them through seed-caching. They may also contribute to the distribution of truffle fungal spores when they eat truffles. They are an important prey source and parasitic host for other animals.[49]

Predation

[edit]

Eastern gray squirrels predators include hawks, weasels, raccoons, bobcats, foxes, domestic and feral cats, snakes, owls, and dogs.[10][40] Their primary predators are hawks, owls, and snakes.[50] Raccoons and weasels may consume a squirrel depending on where it lives in the United States.[51] Rattlesnakes eat squirrels in California as they are searching for food in a heavy forest.[51] The squirrel is susceptible to being eaten by foxes in the eastern region of the United States.[51]

In its introduced range in South Africa, it has been preyed on by African harrier-hawks.[52] When a predator is approaching the eastern gray squirrel, other squirrels will inform the squirrel of the predator by sending an acoustic signal to let the squirrel know. The speed of a squirrel makes it hard for it to be captured by the predators.[53]

Diet

[edit]
Hazelnuts gnawed by gray squirrel; the curved cut marks left by the sharp incisors are visible around the holes

Eastern gray squirrels eat a range of foods, such as many types of seeds and nuts, including acorns, walnuts, and hazelnuts, tree buds, flowers,[54] berries, tree bark, and some types of forest fungi, including fly agaric mushrooms[55] and truffles.[40] They are also carnivorous, variously eating insects, small birds, eggs, frogs, lizards, and other small rodents,[56] including other squirrels.[57]

Eastern tree squirrels can cause damage to trees by tearing the bark and eating the soft cambial tissue underneath. In Europe, sycamore and beech suffer the greatest damage.[58] Mast-bearing gymnosperms such as cedar, hemlock, pine, and spruce are another food source,[54] as well as angiosperms such as hickory, oak, and walnut. These trees produce important foods for them during the spring and fall months. Tree squirrels will vary the species they forage upon seasonally.[47] Tree squirrels also raid gardens for wheat,[54] tomatoes, corn, strawberries, and other garden crops.[59] Sometimes they eat the tomato seeds and discard the rest. On occasion, eastern gray squirrels also prey upon insects, frogs, small rodents including other squirrels, and small birds, their eggs, and young.[3][40] They also gnaw on bones, antlers, and turtle shells – likely as a source of minerals scarce in their normal diet.[55] In urban and suburban areas, these squirrels scavenge for food in trash bins. However, these foods are not safe for them to digest because they include sugar, fat, as well as additives that can make them sick. Eastern gray squirrels are sometimes mistakenly thought to be herbivores, but they are omnivores.[60]

Eastern gray squirrels have a high enough tolerance for humans to inhabit residential neighborhoods and raid bird feeders for millet, corn, and sunflower seeds. Some people who feed and watch birds for entertainment also intentionally feed seeds and nuts to squirrels for the same reason.[61] However, in the UK eastern gray squirrels can take a significant proportion of supplementary food from feeders, preventing access and reducing use by wild birds.[62] Attraction to supplementary feeders can increase local bird nest predation, as eastern gray squirrels are more likely to forage near feeders, resulting in increased likelihood of finding nests, eggs and nestlings of small passerines.[63]

Eating a cicada
Eating a mushroom
Gnawing on a goat skull
Eating a small bird
Eating an apple
Eating a conifer cone
Eating an acorn
Eating an ice cream cone

Introductions and impact

[edit]
The eastern gray squirrel is considered an invasive species in the UK (Bunhill Fields, London)

The eastern gray squirrel is an introduced species in a variety of locations in western North America: in western Canada, to the southwest corner of British Columbia and to the city of Calgary, Alberta;[19] in the United States, to the states of Washington and Oregon and, in California, to the city of San Francisco and the San Francisco Peninsula area in San Mateo and Santa Clara Counties, south of the city. It has become the most common squirrel in many urban and suburban habitats in western North America, from north of central California to southwest British Columbia.

By the turn of the 20th century, breeding populations of the eastern gray squirrel had been introduced into South Africa, Ireland, Italy, Australia (extirpated by 1973), and the United Kingdom.[64]

In South Africa, though exotic, it is not usually considered an invasive species owing to its small range (only found in the extreme southwestern part of the Western Cape, going north as far as the small farming town of Franschhoek), as well because it inhabits urban areas and places greatly affected by humans, such as agricultural areas and exotic pine plantations. Here, it mostly eats acorns and pine seeds, although it will take indigenous and commercial fruit, as well.[65] Even so, it is unable to use the natural vegetation (fynbos) found in the area, a factor which has helped to limit its spread.[66] It does not come into contact with native squirrels due to geographic isolation (a native tree squirrel, Paraxerus cepapi, is found only in the savanna regions in the northeast of the country)[67] and different habitats.

Gray squirrels were first introduced to Britain in the 1870s, as fashionable additions to estates.[68] In 1921 it was reported in The Times that the Zoological Society of London had released eastern greys to breed at liberty in Regents Park:

A dozen years ago the Zoological Society of London obtained a number from a private collection in Bedfordshire for the purpose of inducing them to breed at liberty in the Gardens in Regent's Park. They were first kept in a large enclosure from which, when they had become used to visitors, they were allowed to pass in and out by a rope bridge to a tree. It was hoped that they would spread from the Gardens to the Park. After two or three years in which they seemed to be disappearing, they suddenly became ubiquitous...The grey squirrels are plainly happy and plainly give happiness to Londoners...On the other hand, grey squirrels, whether by taking advantage of tubes and buses, or by deliberate human connivance, have spread from London and are invading the country over very wide areas. They are said to drive out the red squirrel, to raid gardens, and to add to the anxieties of the pheasant breeder. We hope that fuller inquiry will not sustain these charges.[69]

They spread rapidly across England, and then became established in both Wales and parts of southern Scotland. On mainland Britain, they have almost entirely displaced native red squirrels. Larger than red squirrels and capable of storing up to four times more fat, gray squirrels are better able to survive winter conditions. They produce more young and can live at higher densities. Gray squirrels also carry the squirrelpox virus, to which red squirrels have no immunity. When an infected gray squirrel introduces squirrelpox to a red squirrel population, its decline is 17–25 times greater than through competition alone.[68]

In Ireland, the displacement of red squirrels has not been as rapid because only a single introduction occurred, in County Longford. Schemes have been introduced to control the population of gray squirrels in Ireland to encourage the native red squirrels. Eastern gray squirrels have also been introduced to Italy, and the European Union has expressed concern that they will similarly displace the red squirrel from parts of the European continent.

As food

[edit]
Main article: Tree squirrel § As game

Gray squirrels were eaten in earlier times by Native Americans and their meat is still popular with hunters across most of their range in North America. Today, it is still available for human consumption and is occasionally sold in the United Kingdom.[70] However, physicians in the United States have warned that squirrel brains should not be eaten, because of the risk that they may carry Creutzfeldt–Jakob disease.[71]

Displacement of red squirrels

[edit]
Further information: Eastern gray squirrels in Europe
An eastern gray squirrel and a red squirrel eating seeds

In Britain and Ireland, the eastern gray squirrel is not regulated by natural predators,[72] other than the European pine marten, which is generally absent from England and Wales.[73] This has aided its rapid population growth and has led to the species being classed as a pest and it is now illegal to release captured eastern grey squirrels back into the wild in the UK.[74] Measures are being devised to reduce its numbers, including a campaign starting in 2006 named "Save Our Squirrels" using the slogan "Save a red, eat a grey!" which attempted to re-introduce squirrel meat in to the local market, with celebrity chefs promoting the idea,[75] cookbooks introducing recipes containing squirrel and the Forestry Commission providing a regular supply of squirrel meat to British restaurants, factories and butchers.[76] In areas where relict populations of red squirrels survive, such as the islands of Anglesey, Brownsea and the Isle of Wight, programs exist to eradicate gray squirrels and prevent them from reaching these areas in order to allow red squirrel populations to recover and grow.[77]

Although complex and controversial, the main factor in the eastern gray squirrel's displacement of the red squirrel is thought to be its greater fitness, hence a competitive advantage over the red squirrel on all measures.[78] Within 15 years of the grey squirrel's introduction to a red squirrel habitat, red squirrel populations are extinct.[79] The eastern gray squirrel tends to be larger and stronger than the red squirrel and has been shown to have a greater ability to store fat for winter. Due to the dearth of trees in their native Ireland for them to reside in, red squirrels are the only species being harmed by the invasion of grey squirrels.[79] The squirrel can, therefore, compete more effectively for a larger share of the available food, resulting in relatively lower survival and breeding rates among the red squirrel. Parapoxvirus may also be a strongly contributing factor; red squirrels have long been fatally affected by the disease, while the eastern gray squirrels are unaffected, but thought to be carriers – although how the virus is transmitted has yet to be determined. Red squirrel extinction rates can be 20–25 times greater in areas with confirmed cases of squirrel pox than they are in areas without the disease.[79] This competitive action done between these two squirrels is reasoned to qualify the eastern gray squirrel as a keystone species because since the eastern gray squirrel is coming and wiping out the red squirrels, there would be a reduced chance of competition hence more eastern gray squirrels will come in to Ireland.[80] However, several cases of red squirrels surviving have been reported, as they have developed an immunity – although their population is still being massively affected. The red squirrel is also less tolerant of habitat destruction and fragmentation, which has led to its population decline, while the more adaptable eastern gray squirrel has taken advantage and expanded. Methods done to control this competition between these squirrels are that red squirrels should remain in their original habitats, such as Ireland, while the grey squirrels should be kept out of these places entirely as a means of controlling this squirrel competition.[79]

Similar factors appear to have been at play in the Pacific region of North America, where the native American red squirrel has been largely displaced by the eastern gray squirrel in parks and forests throughout much of the region.

Ironically, "fears" for the future of the eastern gray squirrel arose in 2008, as the melanistic form (black) began to spread through the southern British population.[81] In the UK, if a "grey squirrel" (eastern gray squirrel) is trapped, under the Wildlife and Countryside Act 1981, it is illegal to release it or to allow it to escape into the wild; instead, it is legally required be "humanely dispatched."[82]

In the late 1990s, Italy's National Wildlife Institute and University of Turin launched an eradication attempt to halt the spread of gray squirrels in northwest Italy, but court action by animal rights groups blocked this. Hence gray squirrels are expected to cross the Alps into France and Switzerland in the next few decades.[83][84]

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Eastern gray squirrel

View on Grokipedia
from Grokipedia
The eastern gray squirrel (Sciurus carolinensis) is a medium-sized arboreal rodent native to the deciduous hardwood forests of eastern and central North America, typically measuring 16 to 20 inches in length with soft gray fur, a white underbelly, large dark eyes, and a prominent bushy tail used for balance and signaling.[1][2] Primarily diurnal and omnivorous, it forages for acorns, hickory nuts, seeds, berries, fungi, and insects, occasionally preying on bird eggs, nestlings, or small vertebrates, while caching excess food in the ground or tree cavities to sustain it through winter scarcity.[3][4][5] Highly adaptable, it thrives in both rural woodlands and urban parks, constructing dreys (leafy nests) in tree canopies for shelter and reproduction, with females producing one to two litters annually of 2–4 young after a 44-day gestation.[6][2] Introduced to Europe in the late 19th and early 20th centuries, the species has established feral populations in the United Kingdom, Ireland, and Italy, where it spreads tree diseases like bark-stripping that damage timber and outcompetes the native Eurasian red squirrel (Sciurus vulgaris) through superior resource exploitation and possible disease transmission, leading to local extirpations of the red squirrel.[7][8] Classified as Least Concern by the IUCN due to its wide native distribution and stable populations, it faces no major conservation threats in its homeland but is managed as a pest in introduced ranges.[9]

Taxonomy and Etymology

Taxonomy

The eastern gray squirrel (Sciurus carolinensis Gmelin, 1788) is a species of tree squirrel classified within the family Sciuridae.[10][11] The binomial name was first described by Johann Friedrich Gmelin in Systema Naturae (13th edition), based on specimens from the Carolinas.[11][12] Its taxonomic hierarchy is as follows:
  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Mammalia
  • Order: Rodentia
  • Family: Sciuridae
  • Genus: Sciurus
  • Species: S. carolinensis[10][13][14]
Five subspecies are currently recognized, differentiated primarily by geographic distribution and subtle morphological variations such as pelage color and size: S. c. carolinensis (nominal, southeastern U.S.), S. c. extimus (southern Florida), S. c. fuliginosus (Appalachian region), S. c. hypophaeus (Gulf Coast), and S. c. leucotis (northern and western ranges).[15] These distinctions arise from regional adaptations but show genetic continuity across populations, with no major phylogenetic breaks indicating separate species status. Melanistic (black) forms, common in some introduced populations, represent color morphs within subspecies rather than distinct taxa.[16]

Etymology

The binomial name Sciurus carolinensis derives from the genus Sciurus, a Latinization of the Ancient Greek σκίουρος (skiouros), combining σκιά (skia, "shadow" or "shade") and οὐρά (oura, "tail"), which alludes to the bushy tail casting a shadow as the squirrel sits with it arched over its back. The specific epithet carolinensis refers to the Carolinas—the type locality in the southeastern United States from which specimens were first described—as designated by Johann Friedrich Gmelin in his 1788 Systema Naturae.[17] The common name "eastern gray squirrel" descriptively indicates the species' predominant gray pelage and its native range across the eastern deciduous forests of North America, east of the Great Plains and Rocky Mountains, to differentiate it from western congeners like Sciurus griseus.[18]

Physical Characteristics

Morphology and Size

The eastern gray squirrel (Sciurus carolinensis) is a medium-sized tree squirrel with a body adapted for arboreal life, featuring a slender torso, elongated hind limbs for leaping between branches, and strong, curved claws on all digits for gripping bark and foliage.[19] Its forelimbs are shorter than the hind limbs, facilitating climbing and suspension, while the pentadactyl feet possess flexible ankles and elongated metacarpals and metatarsals that enhance dexterity on narrow substrates.[20] The tail is long and bushy, comprising nearly half the total body length and serving functions in balance, propulsion during jumps, and thermoregulation.[19] The skull is relatively elongated with large orbits supporting forward-facing eyes for improved depth perception, essential for navigating complex forest canopies.[19] Adults exhibit no sexual dimorphism in size or external morphology, with total length ranging from 380 to 525 mm, including a tail of 150 to 250 mm; hind foot length measures 54 to 76 mm, and ear length from notch is 25 to 33 mm.[19] Body weight typically varies between 400 and 800 g, averaging 550 to 600 g, though individuals may reach up to 1 kg in northern populations where fat reserves accumulate seasonally.[21] [22] Newborns weigh 13 to 18 g, attaining adult dimensions by approximately 9 months of age.[19] The dentition consists of 22 teeth with a formula of I 1/1, C 0/0, P 2/1, M 3/3 = 22, featuring continuously growing incisors suited for gnawing hard nuts and bark.[19] Hindlimb musculature, particularly the extensors, is robust, enabling force generation and length changes critical for powerful jumps and rapid acceleration in trees.[23]
MeasurementRange
Total length380–525 mm[19]
Tail length150–250 mm[19]
Hind foot length54–76 mm[19]
Weight400–800 g (avg. 550–600 g)[21]

Growth and Lifespan

Newborn Eastern gray squirrels (Sciurus carolinensis) are altricial, born hairless, blind, and weighing 10–18 grams, with a body length of approximately 5–6 cm.[24] Skin pigmentation emerges around 14 days postpartum, followed by initial hair growth on the back, with complete fur development by 3 weeks of age.[24] Ears open at about 3 weeks, lower incisors erupt shortly thereafter, upper incisors appear by 5 weeks, and eyes open between 4 and 5 weeks.[25] Weaning begins in the seventh week and concludes by the tenth week, at which point juveniles weigh around 200 grams.[19][26] Juveniles become independent from the mother between 10 and 12 weeks of age, transitioning to foraging behaviors while still developing motor skills and pelage changes from juvenile to adult patterns.[19] Body mass classifications progress from juveniles under 200 grams to subadults at 200–500 grams and adults exceeding 500 grams, with full adult size and mass achieved by 9 months.[27][19] Sexual maturity typically occurs around 11 months for males and 6–11 months for females, though earliest reproduction in females has been recorded at 5.5 months under optimal conditions, with most delaying until over 1 year.[19][3] In the wild, average lifespan is approximately 6 years, limited primarily by predation from hawks, owls, and mammals, though maximum recorded longevity reaches 12 years.[28][5] In captivity, without such pressures, individuals can live up to 20 years.[5][28] High juvenile mortality contributes to low survival rates to adulthood, with only a fraction reaching reproductive age.[5]

Color Morphs and Genetics

The Eastern gray squirrel (Sciurus carolinensis) displays three primary coat color morphs: the wild-type gray, jet-black melanistic, and brown-black intermediate forms. These variations arise from allelic differences at the melanocortin 1 receptor (MC1R) locus.[29] The melanistic phenotypes result from a 24-base-pair deletion (MC1RΔ24) in the MC1R gene, which encodes a receptor involved in melanin production regulation. This mutation, identified in populations from North America and introduced to Europe, leads to increased eumelanin synthesis, darkening the fur.[30] The MC1RΔ24 allele exhibits incomplete dominance over the wild-type allele. Homozygous individuals (MC1RΔ24/Δ24) exhibit jet-black fur due to maximal melanism, while heterozygotes (MC1RΔ24/wild-type) produce a brown-black morph with partial pigmentation reduction in lighter bands. Wild-type homozygotes (wild-type/wild-type) display the standard gray coat with agouti banding.[29] This genetic basis was confirmed through sequencing of MC1R exons in melanistic and gray squirrels from Ontario, revealing the deletion at amino acid positions 87-94 as the causative variant.[30] Melanistic morphs occur at higher frequencies in urban and northern environments, potentially due to selective advantages such as thermoregulation or camouflage against human-modified landscapes, though frequencies vary regionally from less than 1% in southern ranges to over 50% in some introduced populations.[31] Rare hypomelanistic white morphs include albinos, characterized by complete melanin absence due to recessive mutations in tyrosinase-related genes, resulting in white fur, pink skin, and red eyes; and leucistic individuals, with partial pigment loss from recessive alleles affecting multiple pigmentation pathways, retaining dark eyes but reduced fur coloration.[32] These white forms are infrequent, with albinism estimated at rates below 1 in 10,000 in wild populations, increasing vulnerability to predation and UV damage.[33]

Distribution and Habitat

Native Geographic Range

The eastern gray squirrel (Sciurus carolinensis) is native to the eastern deciduous and mixed forests of North America. Its historical distribution spans from the Atlantic seaboard westward to approximately the Mississippi River valley, encompassing much of the eastern and central United States.[19] [3] In the northern extent, the range reaches into southeastern Canada, including southern portions of Ontario, Quebec, and New Brunswick. To the south, it extends through the Appalachian Mountains into northern Florida and eastward Texas, with the species historically absent from the southeastern coastal plains dominated by longleaf pine forests.[3] [15] This range aligns closely with the distribution of mature hardwood forests, particularly oak-hickory associations, which provide essential mast resources. Pre-colonial records and early European accounts confirm the squirrel's abundance in these regions prior to widespread habitat alteration.[19]

Fossil and Evolutionary History

The family Sciuridae originated in North America during the late Eocene epoch, approximately 36 million years ago, based on the earliest known squirrel fossils recovered from western North American deposits.[34] These primitive sciurids exhibited early adaptations for arboreal locomotion, a trait retained in modern tree squirrels. Subsequent diversification within the family during the Oligocene and Miocene included forms like Palaeosciurus goti and P. feignouxi in Europe, which displayed femoral morphologies indicative of primarily arboreal habits in the former and more terrestrial in the latter, suggesting rapid ecological divergence shortly after the family's emergence.[35] The genus Sciurus, encompassing the eastern gray squirrel (S. carolinensis), traces its lineage to the Miocene epoch, with ancestral representatives documented in both North American and European fossil assemblages.[36] This period coincides with climatic shifts and habitat expansions that facilitated the spread of tree-dwelling squirrels across Holarctic regions, driven by forested environments conducive to gliding and caching behaviors observed in extant species. Fossil evidence specific to Sciurus carolinensis appears in the Pleistocene epoch, with remains identified in at least 20 North American localities, the earliest from late Irvingtonian (approximately 1.8–0.78 million years ago) faunas in Florida.[37] [38] During the later Rancholabrean stage (0.78 million–11,700 years ago), the species underwent an increase in body size, potentially linked to expanded deciduous forest habitats and resource availability amid glacial-interglacial cycles.[37] These records indicate S. carolinensis as a relatively recent evolutionary product within Sciurus, adapted to eastern North American woodlands through post-Miocene speciation events.

Introduced Ranges and Adaptations

The Eastern gray squirrel (Sciurus carolinensis) has established populations in multiple non-native regions through deliberate introductions, primarily for ornamental or hunting purposes. In western North America, it was first released in Vancouver's Stanley Park, British Columbia, around 1909–1914, from where it spread across the Lower Mainland and into parts of Washington and Oregon by the mid-20th century.[39] [40] Similar introductions occurred in California and other western U.S. states, often via escapes or releases from parks and estates.[7] In Europe, introductions began in the United Kingdom between 1876 and 1929 at over 30 sites, leading to rapid expansion across England and Wales by the 1950s, with ongoing spread into Scotland.[11] In Italy, four individuals were released in Piedmont in 1948, followed by additional releases in Liguria, resulting in localized populations that have since expanded, particularly in northern regions.[41] The species reached Ireland via the UK and South Africa around 1900 near Cape Town, where it persists in urban and suburban woodlands.[11] Attempts in Australia failed, with populations extirpated by the early 20th century.[7] These introduced populations thrive due to the species' behavioral flexibility and ecological traits suited to temperate deciduous woodlands, mirroring native habitats. Gray squirrels exhibit higher reproductive rates and larger litter sizes compared to native Eurasian red squirrels (Sciurus vulgaris), enabling faster population growth in resource-rich environments.[8] Their generalist diet, emphasizing mast from broadleaf trees like oaks and hazels, provides a competitive edge in human-modified landscapes with abundant hardwoods, where they outforage conifer-dependent natives.[7] In the UK and Italy, displacement of red squirrels stems from direct interference competition, habitat overlap in mixed forests, and transmission of squirrel parapoxvirus, to which grays are resistant but which is lethal to reds.[8] [42] Adaptations to novel environments include exploitation of urban food sources and reduced predation pressure, as few natural predators target adults in introduced areas. In British Columbia, grays occupy similar niches to native Douglas squirrels but show greater tolerance for fragmented urban forests.[43] Bark-stripping damage to trees, observed in both North American and European introductions, reflects unchanged foraging behaviors that exploit non-native timber species.[42] Overall, success derives from pre-adaptation to analogous ecosystems rather than rapid evolutionary changes, compounded by human-facilitated dispersal and limited control efforts.[11] The species is classified among the 100 worst invasive aliens by the IUCN due to biodiversity impacts, prompting eradication programs in Italy and containment in the UK.[7]

Behavior

Activity Patterns and Social Structure

The eastern gray squirrel (Sciurus carolinensis) is strictly diurnal, with activity concentrated during daylight hours and no recorded nocturnal foraging.[44] Peak activity typically occurs in the early morning and late afternoon in spring, summer, and fall, reflecting a bimodal pattern driven by foraging demands and thermoregulation.[45] In winter, this shifts to a unimodal midday peak, as individuals minimize exposure to low temperatures while caching food reserves.[45] Squirrels do not enter true hibernation but exhibit periods of torpor and reduced mobility during severe cold snaps, remaining in insulated dreys to conserve energy.[46] Socially, eastern gray squirrels operate within loose dominance hierarchies rather than rigid packs or territories, with adult males establishing rank over subordinates primarily through age, body size, and agonistic displays such as chasing and upright postures.[47] [5] Home ranges overlap extensively—averaging 2–10 hectares for adults—with minimal aggression except during mating chases or when lactating females aggressively defend nest trees from intruders.[48] Outside of breeding seasons (January–February and June–July in northern ranges), individuals are largely solitary foragers, though they frequently share dreys in groups of 2–9 during autumn and winter for thermoregulation, without forming enduring kin-based troops.[49] [50] This flexible aggregation promotes gene flow across populations via opportunistic mating but limits cooperative behaviors beyond maternal care of litters, where females rear 2–4 young alone for 10–12 weeks post-weaning.[50] Dominance influences access to food patches and mates, with higher-ranked males securing more copulations during synchronized estrus periods.[47]

Communication Methods

Eastern gray squirrels (Sciurus carolinensis) utilize a multimodal communication system encompassing vocalizations, visual displays primarily through tail movements, and olfactory signals via scent marking to convey information about threats, territory, and social status.[51][52][53] Vocalizations serve critical roles in alarm signaling and agonistic interactions. Alarm calls include distinct types such as "kuks" (short, bark-like sounds), "quaas" (longer, moaning barks), and "moans," which differ in acoustic structure to indicate predator proximity or type; for instance, "seet" calls signal terrestrial threats, while combined "seet-bark" variants denote aerial predators.[54][55] These calls prompt conspecifics to increase vigilance or flee, with variation in call rate and duration correlating to perceived risk levels.[55] In social contexts, tooth-chattering—a rapid, grinding sound produced by the teeth—occurs during territorial disputes or nestmate aggression, escalating with resource competition among juveniles.[51] Other sounds, such as muk-muks (cooing purrs), facilitate non-alarm interactions like mating or group coordination.[56] Visual signals rely heavily on tail positioning and movement, integrated with vocal cues for enhanced efficacy in alarm contexts. Tail flicking and flagging (rapid waving) accompany vocal alarms to amplify threat detection, with recipients responding more robustly to combined multimodal signals than to either alone, suggesting redundancy for reliability in noisy or obstructed environments.[52] In agonistic encounters, specific tail postures communicate intent: a raised, arched tail signals dominance or warning, while piloerection (fluffing) intensifies displays during confrontations over food or mates.[57] Ear rotations also provide directional cues during threat assessment.[51] Olfactory communication involves scent marking to delineate territories and convey individual identity. Squirrels rub oral scent glands on branches or conspecifics via chin-rubbing, depositing lipids that signal ownership and deter intruders, with marking frequency higher in males during breeding seasons.[53][58] Urine marking supplements this, applied to prominent sites to advertise presence, particularly by dominant individuals, though females mark less frequently outside estrus.[59] These chemical signals persist in the environment, enabling asynchronous communication over territories spanning 1-10 hectares depending on habitat density.[53] Tactile interactions, such as grooming or nuzzling, occur primarily between mothers and offspring or mating pairs but are subordinate to other modalities.[51]

Reproductive Biology

Eastern gray squirrels exhibit two breeding seasons per year, typically from December to February and from May to June, with timing varying slightly by latitude.[60][19] During estrus, which lasts about 8 hours for females, multiple males engage in aggressive chases and competitions to mate with the receptive female, often resulting in hierarchical dominance displays.[61] Copulation bouts can last from 1 to 25 minutes.[62] Gestation lasts approximately 44 days (range 42-46 days), after which females give birth to litters averaging 2-4 altricial young, though sizes up to 8 have been recorded.[60][63] Newborns are blind, hairless, and weigh about 13-15 grams, relying entirely on maternal care.[64] Females provide milk for 7-10 weeks and frequently relocate litters between tree cavities and leafy dreys to evade predators or parasites.[3] Sexual maturity is attained at 9-12 months of age, with females often breeding in their first year and males slightly later.[3][60] Young become independent around 10-12 weeks post-birth, dispersing to establish territories, though first-year survival rates are low due to predation and environmental factors.[65] Males do not participate in parental care, focusing instead on future mating opportunities.[19]

Predation Risks and Defenses

Eastern gray squirrels (Sciurus carolinensis) are preyed upon by diverse predators, including raptors such as Cooper's hawks, red-tailed hawks, and various owls, which target both adults and juveniles during foraging or nesting.[66][19] Mammalian predators encompass red foxes, coyotes, bobcats, raccoons (notably preying on nestlings), American mink, and weasels, with raccoons documented as a major cause of juvenile mortality in forested habitats.[66][4] Domestic cats and dogs contribute significantly to predation in suburban and urban settings, exacerbating risks for ground-foraging individuals.[22] Predation imposes high mortality, particularly on first-year squirrels, with overall juvenile survival rates ranging from 25% to 40%; in monitored northern populations, avian predation accounted for 25% of attributed deaths, and mammalian predation for 34%.[22][67][68] To mitigate these threats, eastern gray squirrels rely on acute sensory detection and rapid evasion tactics. Upon spotting a predator, individuals emit loud alarm calls—such as barks, chatters, or muk-muk warnings—to alert nearby conspecifics and signal to the predator that it has been detected, potentially reducing attack success.[69][70] These vocalizations vary by threat type, with higher-pitched calls for aerial predators and barking for terrestrial ones.[19] Squirrels maintain vigilance through behaviors like bipedal scanning while foraging, which allows early threat identification and minimizes exposure time on the ground.[71] Physically, their adaptations emphasize arboreal escape: squirrels ascend tree trunks swiftly, circling to the opposite side to evade pursuit, and leap between branches with high agility, leveraging strong claws and muscular limbs.[19] Dense canopy cover in preferred habitats conceals them from aerial hunters, while their gray pelage provides bark-like camouflage during immobility.[72] Diurnal foraging patterns further reduce encounters with nocturnal owls, though this leaves them vulnerable to daytime raptors.[66] Juveniles in leafy dreys face elevated nest predation, prompting females to select elevated, concealed sites for litters.[4] Despite these defenses, predation remains a primary limiter of population growth, with effectiveness tied to habitat structure and predator density.[67]

Diet and Foraging

Primary Food Sources

The Eastern gray squirrel (Sciurus carolinensis) primarily consumes hard mast, such as acorns, hickory nuts (Carya spp.), and beechnuts (Fagus grandifolia), which constitute the core of its diet, especially during fall and winter when these resources peak in availability.[73] Tree seeds overall represent the principal food source, with squirrels exhibiting strong dependence on mast crops for energy storage and survival through periods of scarcity.[74] [75] Fungi, particularly hypogeous truffles from genera like Rhizopogon and Geopora, form a significant secondary component, often consumed when mast production is low, though squirrels prefer tree seeds when available.[75] In summer months, fungi can comprise up to 27.1% of the diet in certain regions, providing essential nutrients and aiding in spore dispersal.[76] The diet also includes buds, flowers, seeds, fruits, and bark, but these are opportunistic rather than primary.[77] While omnivorous, animal matter such as insects, bird eggs, and small vertebrates is eaten infrequently and does not dominate the dietary composition.[78] Dependence on mast drives population fluctuations, with abundant crops supporting higher densities and reproduction rates.[79]

Foraging Strategies and Caching

Eastern gray squirrels (Sciurus carolinensis) primarily utilize scatter-hoarding as their caching strategy, burying single nuts or small quantities in dispersed locations throughout their home range to reduce the risk of pilferage by conspecifics or other animals.[74] This obligate behavior contrasts with larder-hoarding species that concentrate stores in centralized depots, as scatter-hoarding minimizes total loss when caches are stolen by distributing resources widely.[80] Caching activity intensifies in autumn when mast crops like acorns and hickory nuts are abundant, allowing squirrels to amass reserves for winter survival when fresh food is scarce.[81] Foraging precedes caching, involving active search in trees and on the ground for seeds, nuts, fungi, and occasionally insects or eggs, with decisions to consume immediately or cache influenced by nut quality and environmental cues.[82] Squirrels assess food items tactilely, often handling potential caches to evaluate size and viability before burial, and adjust strategies based on perceived risks; for instance, they cache preferred foods in open areas where pilferage risk is lower despite higher predation exposure.[83] In the presence of competitors or observers, foraging efficiency declines, with squirrels exhibiting slower, more error-prone handling and reduced intake, prompting pilferage avoidance tactics such as deceptive caching—pretending to bury items without actually doing so.[82][84] Retrieval relies on spatial memory, enabling squirrels to relocate up to 24 caches over periods extending to two months, supplemented by olfactory cues for precise excavation.[85] Social influences persist during caching, as the proximity of conspecifics alters site selection and burial depth to thwart theft, with evidence indicating continued adjustment even after initial observation.[86] Models of optimal hoarding predict rapid initial caching near food sources followed by longer travel times for subsequent dispersals, a pattern observed in response to varying food availability and competition levels.[84] While memory facilitates recovery of a significant portion of caches, incomplete retrieval contributes to unintended seed dispersal, though this foraging tactic prioritizes individual survival over ecological outcomes.[87]

Seasonal and Opportunistic Feeding

The eastern gray squirrel (Sciurus carolinensis) adjusts its feeding patterns seasonally to capitalize on fluctuating resource availability, prioritizing energy-dense foods during periods of scarcity. In autumn, the diet centers on hard mast, including acorns, hickory nuts, and walnuts, which constitute the bulk of consumption and caching efforts to build fat reserves and winter stores; studies in seasonally flooded habitats show squirrels consuming up to 89% more walnuts than acorns when both are available, highlighting selective preferences based on nutritional value.[79] Winter feeding relies heavily on retrieved caches of mast, with supplementation from tree bark, buds, fungi, and occasional scatterhoarded items; hard mast remains critical, comprising a significant portion of stomach contents even in adverse conditions like flooding, where squirrels adapt by increasing intake of alternative plants, totaling 21 species observed across fall and winter.[79][63] In spring, squirrels shift to tender buds from species like maple, tulip poplar, flowering dogwood, and black cherry, alongside early insects and flowers, providing hydration and proteins during breeding.[3] Summer expands to include berries, fruits, seeds, mushrooms, and heightened animal matter such as invertebrates, reflecting peak vegetative growth.[88] Opportunistically, eastern gray squirrels incorporate non-native or supplemental items regardless of season, including fungi like truffles, bird eggs, nestlings, and in urban areas, anthropogenic waste from trash bins and bird feeders; urban populations show elevated trash foraging in warmer months, with diets diversifying to cookies, ice cream, and other human discards during shortages.[89][78][90] This flexibility enhances survival in varied habitats, though it can lead to nutritional imbalances from processed foods.[78]

Ecological Role

Interactions Within Native Ecosystems

Eastern gray squirrels (Sciurus carolinensis) contribute to native ecosystem dynamics primarily through seed dispersal via scatter-hoarding. They bury nuts such as acorns from oaks (Quercus spp.) and hickory nuts (Carya spp.) in numerous small caches across forest floors, often forgetting locations of 20-30% of these, which allows for seedling germination and establishment. This behavior promotes regeneration of hardwood-dominated forests in their native range across eastern North America, where oak-hickory woodlands prevail, with studies showing enhanced seedling survival rates due to reduced predation on dispersed seeds compared to clumped hoards.[91][92][19] As mid-trophic level herbivores and omnivores, they serve as prey for native predators including raptors like red-tailed hawks (Buteo jamaicensis) and barred owls (Strix varia), and mammals such as coyotes (Canis latrans), red foxes (Vulpes vulpes), and bobcats (Lynx rufus). Juveniles face higher predation risk, with first-year mortality rates exceeding 50% in some populations, integrating squirrels into food web cascades that regulate predator-prey balances in deciduous and mixed forests.[19][68] Eastern gray squirrels also exert top-down pressure as predators on invertebrates, bird eggs, and nestlings, potentially influencing insect populations and avian reproductive success in native habitats. They consume fungi including truffles, aiding mycorrhizal spore dispersal and supporting belowground plant-fungal symbioses essential for forest nutrient cycling. In sympatric zones with congeneric species like fox squirrels (Sciurus niger), resource partitioning occurs, with grays favoring denser canopies and exploiting different mast crops to minimize direct competition. These interactions maintain biodiversity without evidence of dominance or displacement in equilibrium native systems.[19][14]

Symbiotic and Competitive Relationships

The eastern gray squirrel (Sciurus carolinensis) maintains mutualistic relationships with oak species (Quercus spp.), primarily through scatter-hoarding of acorns, which promotes seed dispersal and forest regeneration. Squirrels cache thousands of acorns annually, retrieving approximately 75-95% but leaving forgotten caches to germinate, particularly favoring red oak acorns due to their tannin content and delayed germination, which aligns with the squirrels' caching timeline of several months.[93] [94] This symbiosis benefits oaks by expanding their range beyond parent trees—up to 100 meters or more—while providing squirrels with a reliable, pilfer-resistant food reserve during winter scarcity. Empirical studies confirm that oak seedling establishment correlates positively with squirrel caching density, with dispersal distances averaging 10-60 meters in fragmented habitats.[95] Eastern gray squirrels also interact mutualistically with hypogeous (truffle-like) fungi, consuming them as a dietary component—comprising up to 10-20% of summer intake in some populations—and dispersing viable spores via scat over distances of several kilometers.[96] [75] This mycophagy supports fungal colonization of tree roots, enhancing nutrient uptake for host plants like conifers and hardwoods, which indirectly sustains the squirrels' arboreal habitat and food web. Such dispersal is crucial for fungi lacking airborne spores, with squirrel feces containing 10^4-10^6 spores per gram, facilitating ectomycorrhizal networks in forest soils.[97] In competitive contexts, introduced eastern gray squirrels in Europe exert strong exploitative and interference competition against native Eurasian red squirrels (Sciurus vulgaris), dominating shared resources like hazelnuts, acorns, and tree cavities, leading to 20-80% reductions in red squirrel density within 10-15 years of gray arrival.[8] [98] Grays achieve this through higher foraging efficiency, broader dietary tolerance (including human food waste), and larger litter sizes (2-4 young per female annually versus reds' 3-7 but with higher juvenile mortality), resulting in asymmetric resource depletion; for instance, grays deplete cached seeds 1.5-2 times faster than reds in mixed woodlands.[99] In native North American ranges, competition is milder, with spatial partitioning against fox squirrels (S. niger)—grays favoring mature forests while foxes exploit edges—and temporal avoidance with American red squirrels (Tamiasciurus hudsonicus), reducing overlap in peak foraging times by 30-50%.[100] However, in high-density urban or mast-failure years, grays can displace smaller congeners from prime feeding patches via aggressive chases and cache pilfering.[71]

Population Dynamics and Adaptability

In its native eastern North American range, the eastern gray squirrel (Sciurus carolinensis) exhibits population dynamics strongly influenced by cyclic fluctuations in hard mast production, particularly acorns from oaks (Quercus spp.). Abundant mast years trigger increased reproduction, with females producing two litters annually (spring and late summer), each averaging 2-4 young, leading to population surges; conversely, mast failures result in high overwinter mortality from starvation and predation, causing declines of up to 80-90% in some areas.[72][101][21] These boom-bust cycles occur every 3-5 years, synchronized with co-occurring species, and maintain average densities of 2-8 individuals per hectare in deciduous forests dominated by mast-producing trees.[102][103] Urban and suburban habitats support higher densities, often 2.5 times those in rural forests, reaching 10-50 per hectare in parks due to reliable anthropogenic food sources and reduced predation.[104][105] Dispersal distances average 1-2 km but can exceed 10 km, facilitating rapid recolonization post-decline and gene flow across fragmented landscapes.[106] The species' adaptability stems from its generalist foraging, flexible caching behaviors, and enhanced cognitive traits, such as superior problem-solving in novel tasks compared to congeneric red squirrels (Sciurus vulgaris), which contribute to its invasive success in Europe.[107] Introduced populations in the UK, starting from escapes in the late 19th century, have expanded at rates of 2-10 km per year, displacing natives through competitive exclusion and disease transmission, aided by broader habitat tolerance and interbreeding enhancing vigor.[108] In North America, urban habituation includes reduced flight responses to humans and exploitation of non-native foods, enabling persistence amid habitat fragmentation.[109] In its native range across eastern North America, particularly in the southeastern United States including the Carolinas (North Carolina and South Carolina, where the species was first described and named carolinensis), the eastern gray squirrel remains abundant and widespread, thriving in deciduous forests, suburban areas, and urban parks. It is the official state mammal of North Carolina and is found in every county. Population densities typically range from 2–8 squirrels per hectare in natural habitats, with higher densities (up to 10–50 per hectare or more in optimal urban or mast-rich areas) due to abundant food and reduced predation. In North Carolina, annual harvest numbers serve as a proxy for population trends and hunting activity: approximately 500,000 squirrels are harvested each year in recent periods. Harvest levels have declined over the decades from higher historical figures, reflecting changes in hunting pressure and participation rather than major population declines, while indicating overall stability. Similar abundance patterns occur in South Carolina and adjacent southeastern states. Populations fluctuate with mast crop availability (e.g., acorns and nuts), with good years boosting reproduction and numbers. The species is classified as Least Concern by the IUCN, with no major threats in its native range, though local nuisance issues arise in urban settings and competition dynamics occur with other squirrels in shared habitats. Although no precise statewide or regional censuses exist for the Carolinas combined, rough extrapolations from habitat coverage (millions of acres of suitable forest and wooded areas) and typical densities suggest a total tree squirrel population (primarily eastern gray) in the low tens of millions (e.g., 10–30 million or more), underscoring the species' ecological prominence in the region.

Health and Diseases

Common Pathogens and Parasites

Eastern gray squirrels (Sciurus carolinensis) commonly host ectoparasites such as fleas (Orchopeas howardi and Hoplopsyllus anomalus), sucking lice (Neohaematopinus sciuropterus), and ixodid ticks including Ixodes scapularis, with the latter serving as vectors for tick-borne pathogens like Borrelia burgdorferi sensu lato, encompassing diverse genotypes that can infect the squirrels themselves.[110] [27] Mites, including those transmitting Hepatozoon griseisciuri, are also documented on hosts in their native range.[111] These arthropods exhibit variable prevalence tied to host density and habitat, with fleas and lice classified as core ectoparasites in suburban and forested populations.[112] Endoparasitic nematodes dominate internal infections, particularly Strongyloides robustus, which achieves prevalences of 56.6% to 73% in sampled populations, often with intensities ranging from 1 to 86 worms per host and minimal clinical signs in native gray squirrels.[110] [113] Other helminths include Trichostrongylus calcaratus (prevalence around 6.5%) and protozoans like coccidia of the genus Eimeria, where up to 44% of individuals may harbor two species and 14% three, primarily affecting the gastrointestinal tract without severe pathology in adults.[110] [114] Blood parasites such as Hepatozoon spp. occur at low intensities, with mild infections noted in 66.7% of examined gray squirrels in regional surveys.[115] Viral pathogens include squirrel parapoxvirus (SQPV), which gray squirrels typically carry asymptomatically, enabling persistence and potential spillover to naive hosts, though outbreaks in natives are rare due to tolerance.[116] Bacterial agents encompass Leptospira spp., Chlamydia spp., and Borrelia burgdorferi, with gray squirrels acting as reservoirs for atypical strains of the latter in endemic areas.[117] [27] Fungal elements like dermatophytes and yeasts are sporadically detected on skin and fur, posing zoonotic risks via direct contact.[118] Protozoans such as Toxoplasma gondii have been identified in tissues, though infection rates and impacts remain understudied in wild populations.[117] Overall, these agents rarely cause epizootics in healthy adults, reflecting evolutionary adaptation in the native range, but co-infections can exacerbate stress in juveniles or nutritionally compromised individuals.[119]

Disease Transmission Dynamics

Eastern gray squirrels (Sciurus carolinensis) function as reservoirs for squirrelpox virus (SQPV), a parapoxvirus endemic to North America, where it causes chronic, often subclinical infections in over 80% of individuals, with persistent viral loads and periodic recrudescence facilitating ongoing transmission within populations. Transmission occurs primarily through direct contact via bites, scratches, or mucosal exposure during agonistic interactions and communal feeding at shared resources, with higher densities in urban and suburban habitats elevating contact rates and infection prevalence. In gray squirrel populations, immune heterogeneity—such as varying viral shedding and resistance—drives epidemic dynamics, enabling the virus to persist endemically without significant population-level mortality, unlike in susceptible co-occurring species.[120][121] In introduced European ranges, gray squirrels transmit SQPV to native Eurasian red squirrels (Sciurus vulgaris), where the virus manifests as acute, lethal squirrelpox disease with near-100% fatality in infected reds due to their lack of co-evolutionary adaptation. Cross-species transmission dynamics involve gray squirrels as asymptomatic carriers introducing the pathogen via direct interspecific aggression, shared dreys, or contaminated environmental fomites like bark-stripped trees and feeders, accelerating red squirrel extirpation in overlapping habitats at rates exceeding 20-fold faster than competition alone. Modeling indicates that SQPV spillover amplifies gray squirrel invasion success by reducing red populations below viable thresholds, with transmission efficiency heightened by grays' higher densities and mobility.[122][123][121] Beyond poxviruses, eastern gray squirrels host diverse genotypes of Borrelia burgdorferi sensu lato, the Lyme disease agent, primarily through ectoparasitic ticks (Ixodes spp.), positioning them as amplifying hosts in enzootic cycles rather than primary reservoirs. In native eastern North American forests, squirrels acquire infected nymphal ticks during ground foraging, subsequently infesting questing larvae that detach to feed on them, perpetuating spirochete transmission to naive hosts including rodents and birds; atypical B. burgdorferi strains in squirrels suggest potential for altered vector competence, though their net contribution to human Lyme incidence remains understudied and secondary to deer-white-footed mouse cycles. Zoonotic risks are vector-mediated, with rare direct pathogen isolation from squirrels indicating limited mammal-to-human contact transmission, but suburban aggregations increase tick exposure opportunities.[27][124] Other pathogens, such as West Nile virus, exhibit mosquito-vectored dynamics in gray squirrels, where infected individuals serve as dead-end hosts with brief viremia insufficient for widespread amplification, though necropsies confirm occasional fatal cases linked to high mosquito densities in summer. Toxoplasmosis transmission involves oocyst shedding in feces, potentially contaminating water sources, but empirical data on gray squirrel roles in hare or human cycles show sporadic, non-dominant involvement. Overall, transmission dynamics underscore gray squirrels' tolerance to endemic pathogens, enabling spillover risks to immunologically naive taxa while minimizing self-limiting effects.[125][126]

Impacts on Individual and Population Health

Eastern gray squirrels exhibit resilience to many pathogens and parasites, with most individuals displaying few clinical signs of disease. Studies of captured populations reveal that over 94% show no macroscopic lesions, though dermatophyte infections occur at prevalences up to 31%, potentially contributing to mild alopecic lesions in a small subset without strong causal correlation or severe outcomes.[118] Urban populations similarly demonstrate robust health, with biochemical and hematological parameters remaining within reference ranges across seasons and minimal abnormalities such as occasional wounds or abscesses.[127] Mange, caused by mites like Sarcoptes scabiei or Notoedres centrifera, can induce individual morbidity through extensive hair loss, skin crusting, pruritus, and secondary bacterial infections, occasionally leading to fatality from hypothermia during winter exposure, though recovery is common in milder cases.[128] Experimental infections with West Nile virus result in transient viremia and mild, self-resolving conjunctivitis in some individuals, with no observed morbidity, mortality, or neurological deficits, despite microscopic lesions in organs like the brain and kidneys.[129] Toxoplasmosis has been documented as a fatal cause in isolated cases, particularly in juveniles or compromised adults.[126] At the population level, diseases exert limited influence on eastern gray squirrel dynamics in their native range, with no recorded outbreaks driving widespread declines. High reproductive rates and adaptability mitigate individual losses, maintaining stable or fluctuating densities primarily influenced by food availability, predation, and anthropogenic factors rather than pathogens.[130] Squirrelpox virus establishes chronic, recurrent infections in over 80% of individuals but typically without symptomatic impact, serving more as a reservoir for transmission to susceptible species like the Eurasian red squirrel rather than causing epizootics in grays.[120] Parasitic burdens, including ectoparasites and helminths, are common but rarely escalate to population-threatening levels, as evidenced by the absence of disease-mediated crashes in North American studies.[118] This tolerance underscores the species' ecological success, where health threats are overshadowed by extrinsic mortality sources like vehicular collisions and habitat fragmentation.

Human Interactions and Impacts

Historical Introductions

The eastern gray squirrel (Sciurus carolinensis), native to the deciduous woodlands of eastern North America from the Atlantic coast to the Great Plains and northward into southeastern Canada, was deliberately introduced to several non-native regions starting in the late 19th century, often for ornamental or hunting purposes on private estates.[11] These releases facilitated rapid population expansions in suitable habitats, contributing to its status as an invasive species in parts of Europe and western North America.[43] In the United Kingdom, the first documented introductions occurred between 1876 and 1929, involving releases of individuals at numerous locations, primarily to enhance parklands and estates as exotic novelties.[131] By the early 20th century, escaped or released animals had established self-sustaining populations, spreading from initial sites in England to much of mainland Britain.[132] Introductions to Ireland followed in 1911, with a release at Castle Forbes in County Longford, leading to localized persistence.[11] On the European continent, releases began later; in Italy, four individuals from Pennsylvania were imported and freed in the Stupinigi Forests near Candiolo, Piedmont, in 1948, marking the initial establishment point, followed by additional releases in Genoa's Nervi Park in 1966.[11] In western Canada, eastern gray squirrels were introduced to Stanley Park in Vancouver, British Columbia, in 1909, with a separate release in Metchosin on Vancouver Island around the same period; these founding populations expanded across the Lower Mainland by the mid-20th century.[133] Attempts to introduce the species to Australia and South Africa in the early 20th century failed to yield widespread establishments, likely due to climatic mismatches and predation.[134]

Competitive Displacement of Other Squirrels

The eastern gray squirrel (Sciurus carolinensis) has displaced the native Eurasian red squirrel (Sciurus vulgaris) in introduced European ranges through interspecific competition. In Britain, gray squirrels were introduced in the late 19th century and expanded rapidly, replacing red squirrels across broadleaved woodlands in England and Wales, where red populations declined by over 75% in affected areas by the 1980s.[8] [135] In northern Italy, introductions began in 1948 with a small number of individuals from the United States, leading to gray squirrel establishment in Piedmont and subsequent displacement of red squirrels, with gray densities reaching 10-20 individuals per hectare in suitable habitats by the 2010s, compared to red squirrels' lower persistence.[8] [136] Competitive mechanisms favor grays due to their superior exploitation of acorns and other mast resources in deciduous forests, higher reproductive output (up to three litters per year versus reds' one or two), and behavioral interference, including dominance at feeding sites that reduces red foraging efficiency by up to 50% in sympatric areas.[135] [137] Grays achieve population densities 2-5 times higher than reds in shared habitats, depleting food supplies faster and forcing reds into suboptimal coniferous areas where grays compete less effectively.[8] [138] While squirrel parapoxvirus, asymptomatic in grays but often fatal to reds, accelerates declines, experimental evidence confirms interference and exploitative competition as primary drivers of replacement, independent of disease in controlled settings.[139] [135] In its native North American range, eastern gray squirrels compete with fox squirrels (Sciurus niger), occasionally displacing them locally in urbanizing deciduous forests through resource dominance and higher densities, as observed in Missouri where fox harvest declines correlated with gray increases from the 1980s onward.[140] [105] Field removals of grays increased fox survival and reproduction by 20-30%, indicating significant competitive pressure, though coexistence persists in heterogeneous habitats.[140] Complete range-wide displacement remains uncommon, unlike in Europe.[105]

Economic and Agricultural Effects

Eastern gray squirrels cause agricultural damage by consuming and gnawing on crops such as maize, fruits, nuts, vegetables, bulbs, and recently sown seeds, particularly in areas adjacent to wooded habitats.[141] [142] In introduced European populations, they threaten orchards and market gardens, with documented impacts on poplar plantations and arable fields in regions like Piedmont, Italy.[142] However, quantitative assessments reveal low overall incidence of crop damage in some surveys, such as minimal effects observed in semi-natural woodlands and agricultural areas of northern Italy.[143] In forestry, bark stripping by Eastern gray squirrels inflicts severe economic losses, primarily affecting hardwood species like beech, oak, and sycamore during late winter and spring, often leading to tree mortality or reduced timber value.[11] [144] In the United Kingdom, where the species is invasive, annual damage costs to the timber industry range from £6 million to £14 million, including lost productivity from trees failing to reach harvestable size and associated control expenses.[145] [141] [146] These impacts are exacerbated in grant-funded plantations, where bark stripping can render up to 40-50% of crops unviable over decades.[147] In their native North American range, economic effects are more balanced, with hunting and trapping providing revenue that offsets localized agricultural and forestry damages; for instance, Mississippi's annual harvest of approximately 2.5 million squirrels generates an economic impact of $12.5 million.[19] While garden and orchard raiding occurs, large-scale crop losses are less pronounced compared to invasive contexts, and bark damage exists but does not dominate industry costs to the same degree.[148] Overall, invasive populations amplify negative economic burdens through both direct damage and management requirements, contrasting with the net positive or neutral contributions in native ecosystems.[149]

Management Strategies and Controversies

In regions where the eastern gray squirrel (Sciurus carolinensis) causes ecological or economic damage, such as forestry bark-stripping in the United Kingdom, management primarily relies on lethal control through shooting and lethal trapping to suppress populations and protect native red squirrels (Sciurus vulgaris).[150] [151] These methods have achieved local eradications, as demonstrated by a seven-year control operation on the Isle of Anglesey, Wales, where genetic analysis confirmed population elimination by 2010 through sustained culling that reduced numbers below viable thresholds.[152] In the United States, where the species is native, strategies focus on mitigating localized damage to crops and trees via exclusion barriers, habitat modification to reduce food availability, and targeted shooting or fumigation in agricultural settings, with integrated pest management emphasizing non-lethal repellents alongside lethal options when populations exceed damage thresholds.[153] Anticoagulant rodenticides like warfarin were historically deployed in UK woodlands for broad-scale control, proving cost-effective for reducing bark damage but discontinued in 2015 following evidence of secondary poisoning in non-target wildlife, including birds of prey.[154] [155] Emerging non-lethal approaches include immunocontraceptive baits, with UK government-funded trials by the Animal and Plant Health Agency achieving sterility in rodents via oral delivery as of 2024, aiming to curb reproduction without killing while addressing public concerns over lethality; field deployment for gray squirrels is projected for evaluation in high-conflict areas by 2026.[156] [157] Volunteer-based monitoring networks in Europe have enhanced detection and rapid response, integrating citizen science with culling to contain spread, as seen in adaptive programs that partitioned resources for prevention and removal.[158] Controversies surrounding management center on the efficacy and ethics of culling, with UK surveys indicating low public acceptance of lethal methods despite recognition of gray squirrels as pests, favoring alternatives like fertility control amid perceptions of cruelty.[154] Critics argue that incomplete culling triggers compensatory population growth due to reduced intraspecific competition and increased resource availability, potentially exacerbating invasions unless eradication thresholds are met, as modeled in spatially explicit simulations showing higher long-term costs for partial interventions compared to thorough removal.[159] Regulatory hurdles under the EU Invasive Alien Species Regulation (1143/2014) prohibit releases and mandate containment, yet enforcement varies, fueling debates over whether gray squirrel impacts on biodiversity—primarily red squirrel displacement via competition and parapoxvirus transmission—are overstated relative to habitat fragmentation by humans.[160] Proponents of intensified control cite empirical data from successful UK sites where red squirrel recoveries followed gray removals, countering claims of negligible ecological harm.[161]

References

  1. Wonders of Wildlife: Eastern Gray Squirrel
  2. Eastern Gray Squirrel: Mammals - Wildlife - Maine.gov
  3. Eastern Gray Squirrel - Maryland DNR
  4. Gray Squirrel | Sciurus carolinensis - Adirondack Nature
  5. Gray Squirrel - SUNY ESF
  6. Eastern Gray Squirrel | Ohio Department of Natural Resources
  7. Sciurus carolinensis - GISD
  8. Interactions between native and invasive species: A systematic ...
  9. A species account of the Eastern gray squirrel (Sciurus carolinensis)
  10. Sciurus carolinensis Gmelin, 1788 - GBIF
  11. Sciurus carolinensis (grey squirrel) | CABI Compendium
  12. Sciurus carolinensis - Organism - Data resources - CNGBdb
  13. Sciurus carolinensis - NCBI
  14. Grey Squirrel (Sciurus carolinensis) - Columbia University
  15. Distribution of the native range of eastern grey squirrels (Sciurus...
  16. Eastern Gray Squirrel Hunting, History, Habitat, and Biology
  17. Eastern Gray Squirrel - Discover Lewis & Clark
  18. Squirrel - Etymology, Origin & Meaning
  19. Sciurus carolinensis (eastern gray squirrel) - Animal Diversity Web
  20. Locomotor kinematics of tree squirrels (Sciurus carolinensis) in free ...
  21. Gray and Fox Squirrels | Oklahoma State University - OSU Extension
  22. Eastern Gray Squirrel - UF/IFAS Extension Sumter County
  23. The hindlimb extensors of an arboreal and a fossorial squirrel
  24. Squirrel Breeding Biology - Gestation, Birth & Kitten Development
  25. Gray Squirrel Management - Alabama Cooperative Extension System
  26. AnAge entry for Sciurus carolinensis
  27. An Invasive Mammal (the Gray Squirrel, Sciurus carolinensis ...
  28. Eastern Gray Squirrel (Sciurus carolinensis) - NYC.gov
  29. The genetic basis of melanism in the gray squirrel (Sciurus ...
  30. Genetic Basis of Melanism in the Gray Squirrel (Sciurus carolinensis)
  31. Parallel evolution of urban–rural clines in melanism in a widespread ...
  32. What's the difference between Albino and Leucistic White Squirrels
  33. Nature's Mysterious Wonders: How Rare is an Albino Squirrel?
  34. Squirrels' Evolutionary Family Tree Reveals Influence of Climate ...
  35. Inferring the locomotor ecology of two of the oldest fossil squirrels
  36. Phylogeny and Zoogeography of Six Squirrel Species of the Genus ...
  37. [PDF] MAMMALIAN SPECIES No. 480, pp. 1-9, 3 figs. - Sciurus carolinensis.
  38. Sciurus carolinensis - Vertebrate Collection | UWSP
  39. Eastern grey squirrel - Invasive Species Council of British Columbia
  40. [PDF] Sciurus carolinensis - Stewardship Centre for BC
  41. Introduction of the American grey squirrel (Sciurus carolinensis) in ...
  42. Grey squirrel Sciurus carolinensis management in Italy - BioOne
  43. [PDF] Impacts and Management of the Alien Eastern Gray Squirrel in Great ...
  44. Squirrel Activity - Wildlife Online
  45. Diurnal and seasonal activity of the grey squirrel (Sciurus carolinensis)
  46. Diurnal and seasonal activity of the grey squirrel (Sciurus carolinensis)
  47. Determinants of social dominance in eastern gray squirrels (Sciurus ...
  48. The Sociable Gray Squirrel | The Outside Story
  49. Squirrel Behaviour - Nest Sharing - Wildlife Online
  50. The Social System of the Grey Squirrel - jstor
  51. Behaviors associated with vocal communication of squirrels - Diggins
  52. Joint tail and vocal alarm signals of gray squirrels (Sciurus ...
  53. Squirrel Behaviour - Scent-marking - Wildlife Online
  54. What are the Squirrels in Your Yard Saying? - Mary Bates, PhD
  55. Squirrel Alarm Calls Are Surprisingly Complex - WIRED
  56. Squirrel Talk: What Does That Noise Mean? | The Outside Story
  57. (PDF) Eastern Gray Squirrels (Sciurus carolinensis) Communicate ...
  58. (PDF) Sex and species biases in scent marking by fox squirrels and ...
  59. Eastern Gray Squirrel Territoriality | - eMammal - WordPress.com
  60. Eastern Gray Squirrel | State of Tennessee Wildlife Resources Agency
  61. [PDF] Alternative reproductive tactics in male eastern gray squirrels
  62. Question book 4 : What do the mating habits of a Grey Squirrel look ...
  63. Gray Squirrel | Outdoor Alabama
  64. [PDF] Eastern Gray Squirrels - Critter Corner - Louisiana Nursery
  65. Rodents for comparative aging studies: from mice to beavers - PMC
  66. Eastern Gray Squirrel - National Park Service
  67. [PDF] Survival and Causes of Mortality in a Northern Population of ...
  68. Nature Notes: Eastern Gray Squirrel - Harpswell Heritage Land Trust
  69. Eastern Gray Squirrel - Chesapeake Bay Program
  70. How Squirrels Protect Themselves from Predators
  71. Behavioural responses of Eastern grey squirrels, Sciurus ...
  72. Eastern Gray Squirrel | NC State Extension Publications
  73. [PDF] Gray and Fox Squirrels - Oklahoma State University Extension
  74. [PDF] Foraging and feeding behavior of the Eastern Grey Squirrel (Sciurus ...
  75. [PDF] Diets of Native and Introduced Tree Squirrels in Washington
  76. Food Habits of Squirrels in Southeast Ohio - jstor
  77. [PDF] Selection of Agricultural Foods by Eastern Grey Squirrels (Sciurus ...
  78. Gray squirrels consume anthropogenic food waste most often during ...
  79. [PDF] Fall and Winter Diets of Eastern Gray Squirrels in a Seasonally ...
  80. The Evolution of Scatterhoarding Behavior and Behavioral ... - AUETD
  81. Look out for unwanted squirrel hoarding - MSU Extension
  82. Distracted foragers: competitors impair foraging efficiency, accuracy ...
  83. The socioeconomics of food hoarding in wild squirrels - ScienceDirect
  84. Effects of competition and food availability on travel time in scatter ...
  85. Do Squirrels Remember Where They Buried Their Nuts?
  86. Evidence of Social Influences on Cache‐Making by Grey Squirrels ...
  87. Using ecology to guide the study of cognitive and neural ... - NIH
  88. https://exoticnutrition.com/blogs/blog/grey-squirrel-information
  89. [PDF] HIGH RISK FEEDING AND FOOD PREFERENCE IN THE EASTERN ...
  90. Nutrition | Mysite - Squirrel Refuge
  91. Eastern gray squirrels are consistent shoppers of seed traits - PubMed
  92. Squirrels and forest regeneration | ICSRS
  93. Ultimate Basis of the Caching Preferences of Rodents, and the Oak ...
  94. Squirrel-Seed Interactions: The Evolutionary Strategies and Impact ...
  95. The Proximate Basis of the Oak Dispersal Syndrome - BioOne
  96. Diets of native and introduced tree squirrels in Washington
  97. Mammalian mycophagy: A global review of ecosystem interactions ...
  98. Alien species and interspecific competition: effects of introduced ...
  99. Comparative demography of red squirrels (Sciurus vulgaris) and ...
  100. [PDF] Spatial and temporal partitioning between eastern gray and fox ...
  101. [PDF] Eastern Gray Squirrel - management guide
  102. Eastern Gray Squirrel - an overview | ScienceDirect Topics
  103. [PDF] A Comparison of Eastern Gray Squirrel (Sciurus Carolinensis ...
  104. [PDF] Eastern Gray Squirrels (Sciurus carolinensis) Differ in Abundance ...
  105. Urban intensity predicts eastern gray squirrel (Sciurus carolinensis ...
  106. (PDF) Long-Distance Dispersal by Eastern Gray Squirrels in ...
  107. Cognitive Performance of Wild Eastern Gray Squirrels (Sciurus ...
  108. A battle of wits? Problem-solving abilities in invasive eastern grey ...
  109. Eastern Gray Squirrel Behavior in Urban Environments
  110. Macroparasite Fauna of Alien Grey Squirrels (Sciurus carolinensis)
  111. [PDF] The Arthropod Ectosymbionts of the Fox Squirrel in Coles County ...
  112. an investigation of ectoparasite abundance and distribution and tick ...
  113. The price of being bold? Relationship between personality and ...
  114. [PDF] Coccidian parasites of red squirrels (Sciurus vulgaris) and grey ...
  115. [PDF] Blood Parasites of Squirrels from Coles and Lake Counties in Illinois
  116. Effects of Parasitism and Morphology on Squirrelpox Virus ...
  117. Health Status of the Eastern Grey Squirrel (Sciurus carolinensis ...
  118. Health Status of the Eastern Grey Squirrel (Sciurus carolinensis ...
  119. Complex relationships between physiological stress and ... - NIH
  120. The drivers of squirrelpox virus dynamics in its grey squirrel ...
  121. Immune interactions and heterogeneity in transmission drives the ...
  122. Disease threats posed by alien species: the role of a poxvirus in the ...
  123. Poxvirus, red and grey squirrel dynamics: Is the recovery of a ...
  124. https://journals.asm.org/doi/abs/10.1128/aem.00109-15
  125. Pathology Case of the Month - Eastern Gray Squirrel - USGS.gov
  126. Fatal toxoplasmosis in a wild snowshoe hare (Lepus americanus ...
  127. Urban eastern gray squirrels (sciurus carolinensis) show little ...
  128. Squirrel with missing fur. Is it sick? - Purdue University
  129. Experimental Infection of Eastern Gray Squirrels (Sciurus ...
  130. [PDF] Environmental Factors' Effects on Eastern Gray Squirrel (Sciurus ...
  131. Assessing the geographic origin of the invasive grey squirrel using ...
  132. Don't blame grey squirrels: their British invasion had much more to ...
  133. [PDF] The Distribution and Habitat Selection of Introduced Eastern Grey ...
  134. Introduction of the American grey squirrel - (Sciurus carolinensis) in
  135. The Mechanism of Replacement of Red Squirrels by Grey Squirrels
  136. a new threat for endemic red squirrel subspecies | Biological Invasions
  137. Competition between Eurasian red and introduced Eastern grey ...
  138. Declining invasive grey squirrel populations may persist in refugia ...
  139. Interspecific competition affects the expression of personality-traits in ...
  140. Field manipulation of fox and gray squirrel populations
  141. Economic and Environmental Damage Caused by Grey Squirrels
  142. Damage caused by the American grey squirrel (Sciurus carolinensis ...
  143. Damage caused by the American grey squirrel (Sciurus carolinensis ...
  144. Long-term patterns and impacts of grey squirrel debarking in Lady ...
  145. [PDF] An Analysis of the Cost of Grey Squirrel Damage to Woodland
  146. INV0045 - Evidence on Invasive species - UK Parliament Committees
  147. http://www.confor.org.uk/media/247518/forestry-century-grey-squirrels.pdf
  148. Dawn of Squirrelly Bark-Stripping! - BYGL (osu.edu)
  149. (PDF) Economic damage by invasive grey squirrels in Europe
  150. Management of grey squirrels - Forest Research
  151. Controlling the grey squirrel population - Daera
  152. (PDF) Genetic evidence of the effectiveness of grey squirrel control ...
  153. Controlling Eastern Gray Squirrel Damage - Alabama Extension
  154. Public attitudes towards “pest” management: Perceptions on squirrel ...
  155. [PDF] Controlling grey squirrels in forests and woodlands in the UK
  156. Reducing grey squirrel overpopulation: The role of contraceptives in ...
  157. BASC welcomes milestone in grey squirrel fertility control research
  158. [PDF] Evolving grey squirrel management techniques in Europe - REABIC
  159. A spatially explicit population model to compare management using ...
  160. [PDF] Management Measures for Widely Spread Species (WSS) in ...
  161. Editorial: Ecology, impact, and management of squirrel invasions
User Avatar
No comments yet.