| Eastern gray squirrel | |
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| Feeding on maple tree key, Boston | |
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Rodentia |
| Family: | Sciuridae |
| Genus: | Sciurus |
| Subgenus: | Sciurus |
| Species: | S. carolinensis |
| Binomial name | |
| Sciurus carolinensis Gmelin, 1788 |
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| Subspecies[2] | |
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| Range in red (excludes introduced populations) |
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| Synonyms | |
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Matecumbei, Minutus, Hiemalis, Leucotis, Migratorius |
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The eastern gray squirrel or grey squirrel (depending on region) (Sciurus carolinensis), is a tree squirrel in the genus Sciurus native to the eastern and midwestern United States, and to the southerly portions of the eastern provinces of Canada. 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.
A prolific and adaptable species, the eastern gray squirrel has been introduced to, and thrives, in several regions of the western United States. It has also been introduced to Britain, where it has spread across the country and has largely displaced the native red squirrel, Sciurus vulgaris. In Ireland, the red squirrel has been displaced in several eastern counties, though it still remains common in the south and west of the country.[3] There are concerns that such displacement might happen in Italy and that gray squirrels might spread from Italy to other parts of mainland Europe.[4]
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The genus, Sciurus, is derived from two Greek words, skia, meaning shadow, and oura, meaning tail. This name alludes to the squirrel sitting in the shadow of its tail.[5] 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".
As the name suggests, the eastern gray squirrel has predominantly gray fur but it can have a brownish color. It has a white underside and a large bushy tail. Particularly in urban situations where the risk of predation is reduced, both white- 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. There are also genetic variations within these, including individuals with black tails and black colored squirrels with white tails. The head and body length is from 23 to 30 centimetres (9.1 to 12 in), the tail from 19 to 25 centimetres (7.5 to 9.8 in) and the adult weight varies between 400 and 600 grams (14 and 21 oz).[6]
The tracks of an eastern gray squirrel are difficult to distinguish from its cousins the 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 fingers 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 or three feet long.[7]
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.[1] 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 re-burial in a more secure site. Others are more permanent and are not retrieved until months later. It has been estimated that each squirrel makes several thousand caches each season. The squirrels have very accurate spatial memory for the locations of these caches, and use distant and nearby landmarks to retrieve them. Smell is used once the squirrel is within a few centimeters of the cache. It is one of very few mammalian species that can descend a tree head-first. It does this by turning its feet so that the claws of its hindpaws are backward pointing and can grip the tree bark.
Eastern gray squirrels build a type of nest, known as a drey, in the forks of trees. The drey consists mainly of dry leaves and twigs. Squirrels may also nest in the attic or exterior walls of a house. In addition, the squirrel may inhabit a permanent tree den.[8]
Eastern gray squirrels are more active during the early and late hours of the day, and tend to avoid the heat in the middle of a summer day.[8] They do not hibernate.[9]
Predators include humans, hawks, weasels, raccoons, domestic and feral cats, snakes, owls, and dogs. Whilst gray squirrels fight among themselves over food sources, they have been known to mob potential predators such as domestic cats. They also have a complex, tag-team defensive system involving distracting would-be predators with vigorous shaking of their tails.[8]
Eastern gray squirrels breed twice a year, December to February and May to June, though this is slightly delayed in more northern latitudes.[8] The first litter is born in February to March, the second in June to July. There are normally two to six young in each litter, but this number can be as high as 8. The gestation period is about 44 days.[8] The young are weaned at 7 weeks and leave the nest after 10 weeks.
Eastern gray squirrels can start breeding as early as 5 and a half months old,[8] but usually breed for the first time at the age of one.[10] These squirrels can live to be 20 years old in captivity, but in the wild usually only live up to 12.5 years.
As in most other mammals, communication among eastern gray squirrel individuals involves both vocalizations and posturing. It 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. Communications are mainly used in mating season and to ward off predators.
Eastern gray squirrels eat a range of foods such as tree bark, many types of seeds and acorns, walnuts, and other nuts, and some types of fungi found in the forests, including fly agaric mushrooms (Amanita muscaria).[11]
Eastern gray squirrels have a high enough tolerance for humans to inhabit residential neighborhoods and will raid bird feeders for millet, corn, and sunflower seeds. On very rare occasions, when its usual food source is scarce, eastern gray squirrels will also prey upon insects, frogs, small rodents, including other squirrels, and small birds, their eggs and young.[1][12] They will also gnaw on bones, antlers, and turtle shells – likely as a source of minerals sparse in their normal diet.[11]
In the wild, eastern gray squirrels can be found inhabiting large areas of mature, dense woodland ecosystems, that generally cover 40 hectares of land.[12] These forests usually contain large amounts of dense vegetation that provides sufficient amount of food sources and favorable shelters for eastern gray squirrels. 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. Close to human settlements, eastern gray squirrels are found in parks and backyards of houses within urban environments and in the farmlands of rural environments.[13]
The eastern gray squirrel is found in the eastern United States and adjacent southern Canada; New Brunswick to Manitoba, south to eastern Texas and Florida.[1] It has also been introduced into Ireland[14] and Britain, Italy, South Africa, and also Australia (where it was extirpated by 1973).[1]
The eastern gray squirrel has been introduced to a variety of locations in western North America: in Canada, to the southwest corner of British Columbia and to the city of Calgary, Alberta;[15] in the United States, to the states of Washington and Oregon and, in California, to the city of San Francisco and the peninsula area of 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. At the turn of the 19th to 20th century the eastern gray squirrel was introduced into South Africa, Ireland and England.
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 up as far as the small farming town of Franschoek) as well as the fact that 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.[16] Even so, it is unable to utilize the natural vegetation (fynbos) found in the area, a factor which has helped to limit its spread.[17] 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 north-east of the country)[18] and different habitats.
It spread rapidly across England and then became established in both Wales and parts of southern Scotland. On mainland Britain, it has almost entirely displaced the populations of native red squirrels. On the island of Ireland, this displacement has not been as rapid, owing to the fact there was only a single introduction, in County Longford. Schemes have been introduced to control the population in Ireland in order to encourage the native red squirrels. Eastern gray squirrels have also been introduced to Italy, and the European Union has expressed concern that it will similarly displace the red squirrel from parts of the European continent.
In the United Kingdom and in Ireland, the eastern gray squirrel has few natural predators. This has aided its rapid population growth and has led to the species being classed as a pest. Measures are being devised to reduce its numbers, including one plan for celebrity television chefs to promote the idea of eating the squirrels.[19] In areas where relict populations of red squirrel survive, such as the islands of Anglesey and Brownsea, programs seeking to eradicate pest squirrels are in progress in an effort to allow red squirrel populations to recover.[20]
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 and, hence, a competitive advantage over the red squirrel on all measures.[21] 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. 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 are fatally affected by the disease, while the eastern gray squirrels are unaffected but thought to be carriers. 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.
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, 2008 saw the rise of "fears" for the future of the eastern gray squirrel, as the melanistic form (black) began to spread through the southern British population.[22][23] 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 they should be humanely destroyed.[24]
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