Eastern gray squirrel

Name and taxonomy

Johann Friedrich Gmelin named the species Sciurus carolinensis in 1788. The species name points to the Carolinas, where it was first recorded and where it remains very common. The genus name Sciurus comes from two Greek words, skia for shadow and oura for tail. The picture is of a squirrel sitting in the shade of its own tail.

In the United States the word eastern separates it from the western gray squirrel, Sciurus griseus. In Britain and Canada it is just the grey squirrel. GBIF lists five subspecies, among them S. c. pennsylvanicus in the north and S. c. extimus in Florida. GBIF also records names in the Cherokee and Ojibwe languages, a sign of how long people have lived beside it.

Evolution and relatives

The genus Sciurus holds the typical tree squirrels of North America and Eurasia. The eastern gray's closest neighbours in range are the fox squirrel, Sciurus niger, and the western gray squirrel. The fox squirrel is often confused with it, though its belly is brownish orange rather than white. In Europe it meets the smaller Eurasian red squirrel, which belongs to the same genus.

Fossils of the species are known from at least 18 Pleistocene sites across eight US states. Some may date back to the late Irvingtonian stage. A partial humerus and two tibiae from Harleyville, South Carolina, come from beds dated to 18,940 to 18,530 years ago. The site was probably a hardwood and conifer swamp at the time. Body size grew during the early Holocene and then shrank back to the modern size.

Appearance

The head and body measure 23 to 30 centimetres, and the tail another 19 to 25 cm. An adult weighs 400 to 600 grams. Males and females are the same size and colour.

The upper fur is grey, flecked with brown, and the belly is white. The ears are whitish grey, and the tail is grey with a white fringe. Black squirrels are common in the north of the range, and dominate in parts of southeastern Canada. The black coat comes from a partly dominant change in the MC1R gene. At minus 10 degrees Celsius, black squirrels lost 18 percent less heat than grey ones. White squirrels also occur, most often in towns, where predators are few.

The front feet have four toes and the hind feet five. A bounding squirrel lands its hind feet ahead of its front feet, with a stride of 60 to 90 cm. It has 22 teeth, and the incisors grow throughout life, as in every rodent.

Habitat and range

The native range covers the eastern and midwestern United States and the southern edge of central Canada. It runs from New Brunswick, southern Quebec and Ontario and southern Manitoba down to east Texas and Florida. The squirrel is missing from the boreal forest, which has no oaks or hickories. In the mid 1800s the midwestern population was enormous, but hunting and forest clearance nearly removed it from Illinois by 1900.

It prefers mature hardwood forest of 40 hectares or more, with a rich understorey. Oak and hickory woods support the highest densities, because their nuts keep through the winter. A squirrel ranges over 0.61 to 3.24 hectares, and the range shrinks as squirrels grow more numerous. It is equally at home in city parks, suburban gardens and farmland.

Introduced squirrels now live in Washington, Oregon, the San Francisco area, British Columbia and Calgary. Seven pairs released in a Seattle park in 1925 spread across Washington state. Vancouver Island received them in 1966. Overseas populations live in Britain, Ireland, Italy and the Western Cape of South Africa. An Australian population died out by 1973. GBIF holds records from 26 countries.

Diet and feeding

The squirrel is an omnivore, though most of its food is plant matter. ADW lists the nuts, buds and flowers of more than 24 oak species and 10 hickory species, plus pecan, walnut and beech. It also eats maple, elm and mulberry seeds, the cones of pine and spruce, berries, bark and fungi, including truffles. Insects matter in summer, especially for the young. It takes bird eggs and nestlings, frogs, small rodents and even other squirrels. It gnaws bones, antlers and turtle shells, probably for minerals.

The squirrel is a scatter-hoarder. It buries food in many small caches, some for hours, others for months. One squirrel is thought to make several thousand caches a season. It finds them again by spatial memory, using landmarks, with smell as a backup. It often bites out the embryo of an acorn before burial so the nut cannot sprout. If watched, a squirrel may dig a hole, pretend to drop a nut, and cover the empty hole while the nut stays in its mouth.

Near people it raids bird feeders for sunflower seeds, corn and millet. It strips bark to eat the soft tissue beneath, and in Europe sycamore and beech suffer most. Garden crops such as tomatoes, strawberries and corn are also taken.

Behaviour and social life

The squirrel is active by day all year and does not hibernate. In spring, summer and autumn activity peaks about two hours after sunrise and again two to five hours before sunset. In winter there is a single peak in the afternoon. Females are more active in summer and males in winter.

It builds a nest of leaves and twigs, called a drey, in the fork of a tree. A drey is roughly spherical, 30 to 60 cm across, and lined with moss, grass, thistledown and feathers. It also uses hollow tree dens, and a squirrel often keeps two or three at once. Young raised in a den survive better than young in a leaf nest. Squirrels may share a nest in cold weather, and pairs share briefly in the breeding season. In towns they move into attics and wall spaces, where they chew electrical cables.

It can run down a trunk head first by turning its hind feet backwards so the claws grip the bark. Related squirrels may defend a territory together, and a nursing female is aggressive and avoided by others. Males form a dominance order in the breeding season. City squirrels tolerate people closely, which probably reflects generations without hunting.

Communication and senses

The squirrel has a wide range of calls. They include a squeak like a mouse's, a low growling note, a chatter, and a raspy call that biologists write as mehr mehr mehr. The kuk and quaa calls, with tail flicking, warn of a predator and announce when it leaves. A soft purring muk-muk sound passes between a mother and her kits, and a courting male uses it too.

Facial expressions and posture carry meaning as well. City squirrels lean on visual signals, because traffic noise drowns sound and open ground gives a clear view. Forest squirrels rely more on calls under a dense canopy. Smell is keen: a squirrel can read a neighbour's stress and breeding state from scent. Its warning calls also alert other squirrels nearby, which seems to benefit relatives most.

Reproduction and life cycle

Breeding seasons run from December to February and from May to June, a little later in the north. Young mothers usually have one litter in spring. Older females breed again in summer if food is plentiful. In a year of heavy mast, 36 percent of females bear two litters, but in a poor year none do.

Five days before a female comes into heat, males begin to follow her, some from 500 metres away. As many as 34 males may gather. They form a dominance order, and the female mates with several of them. Heat lasts under eight hours, and mating takes under thirty seconds. A wax-like plug then forms in the female and blocks later sperm.

Gestation lasts about 44 days. A litter holds one to four kits, up to eight at most. Newborns weigh 13 to 18 grams and are pink, blind and naked apart from their whiskers. The eyes open at three to six weeks. Weaning starts at seven weeks and ends by ten, and the kits leave the nest after 12 weeks. Only one kit in four lives to its first birthday.

Females usually breed first at about 1.25 years, though a few conceive at five and a half months. Males mature between one and two years. A wild adult typically lives to about 6 years, and the record is 12.5 years in North Carolina. In captivity a squirrel has reached 23.6 years.

Predators and threats

Hawks, owls and snakes are the main predators. Red-tailed hawks, foxes, bobcats, coyotes, wolves, lynx, mink and weasels all take squirrels. Raccoons eat them in some regions, and house cats and dogs kill many in towns. In South Africa the African harrier-hawk has learned to hunt them. Speed and agility in the trees are the squirrel's main defence, along with alarm calls.

Mortality is about 55 percent in the second year and about 30 percent a year after that. Death rates climb sharply again at eight years. Squirrels carry fleas, lice, mites and ticks, and suffer from squirrelpox and fibromatosis, which causes skin tumours. Hunters take large numbers: Mississippi alone harvests about 2.5 million a year. In Britain the grey is culled to protect red squirrels, and releasing a trapped grey is illegal.

Population and conservation

The species is Least Concern on the IUCN Red List and abundant across its native range. Numbers recovered after the crash of the late 1800s as forests regrew and hunting laws arrived. The concern today runs the other way: what the grey does to native squirrels elsewhere.

In Britain, red squirrels vanish within about 15 years of the grey's arrival. The grey is larger, stores up to four times more fat, breeds more and lives at higher density. It also carries squirrelpox, which does not harm it but kills red squirrels. Where the virus is present, red squirrel losses are 17 to 25 times faster than from competition alone. Only the pine marten preys on greys in Britain, and it is largely absent from England and Wales. Island refuges such as Anglesey, Brownsea and the Isle of Wight keep greys out so reds can recover.

Ireland saw a single introduction in County Longford, so the spread has been slower there. Italy holds a growing population, and the EU fears the grey will spread across the continent. Since 2016 EU law bans importing, breeding, selling or releasing the species. In western North America it displaces the western gray squirrel in towns and moist woodland.

Relationship with humans

Native Americans and colonists ate gray squirrels, and hunters across North America still do. Squirrel hunting in Mississippi is worth about 12.5 million dollars a year. US physicians warn against eating squirrel brains because of a possible link to Creutzfeldt-Jakob disease. Among nature watchers, ADW ranks squirrels second only to birds.

The squirrel reached Britain in the 1870s as a fashionable ornament for country estates. The Zoological Society of London released some to breed freely in Regent's Park, and The Times reported in 1921 that they had become ubiquitous. A 2006 campaign called Save Our Squirrels urged Britons to eat grey squirrel. Its slogan asked them to save a red by eating a grey. In Britain the grey ranks second only to the brown rat as a destructive pest of property.

Squirrels can carry plague, typhus and tularemia, and a bite can pass these to people. Their ticks can spread Lyme disease. Even so, most encounters are harmless, and many people feed squirrels in parks for pleasure. In the UK, squirrels at bird feeders take enough food to keep birds away and raid nearby nests.

In culture and myth

In Norse myth, the squirrel Ratatoskr runs up and down the world tree Yggdrasil. He carries insults between the eagle at the crown and the dragon Nidhogg at the roots. The name is usually read as drill-tooth. That squirrel was probably a European red, but the story has attached itself to every squirrel since.

In a Choctaw story an eclipse happens when a black squirrel chews on the sun, and people banged and shouted to drive it away. Wabanaki tales feature Meeko, a spiteful and gossiping squirrel. For several Native American peoples the squirrel stands for preparation and foresight, thanks to its caches. Spirit-animal websites add thrift, energy and playfulness, which seem to be modern readings rather than old ones. In Britain the grey probably has a darker image, as the invader that drove out the red squirrel of children's books.