Red squirrel

Name and taxonomy

Carl Linnaeus described the red squirrel in 1758 and gave it the name Sciurus vulgaris. The type locality was later fixed at Uppsala in Sweden. The species name vulgaris is Latin for common. In much of the world the animal is called the Eurasian red squirrel, to separate it from the American red squirrel of another genus. The genus Sciurus holds the tree squirrels, and its name is thought to come from Greek words for shade and tail.

Naturalists have described more than 40 subspecies, mostly on coat colour. A review in 1971 accepted 16 of them, and the current count stands at 23. Coat colour varies so much within one region that many of these names are doubtful. Two former subspecies are now treated as full species. The Japanese squirrel, Sciurus lis, was split off from the 1960s onward. The Calabrian black squirrel of southern Italy was raised to species rank in 2017.

Evolution and relatives

The red squirrel belongs to the family Sciuridae, which also holds chipmunks, marmots and flying squirrels. Its closest relatives are the other members of Sciurus, such as the Japanese squirrel and the eastern grey squirrel. The Japanese squirrel probably arose when red squirrels reached the Japanese islands in the Pleistocene and were cut off from the mainland. The Calabrian black squirrel descends from one population that became isolated in the Middle Pleistocene. A population in the Sierra Espuna of south-east Spain may also deserve species rank, according to genetic work.

Like other tree squirrels, the red squirrel has a light skeleton and long, heavy hind legs built for leaping. These traits are shared across the genus and probably date from its early history in the forests of Eurasia.

Appearance

The head and body measure 19 to 23 centimetres, and the tail is 15 to 20 cm long. Adults weigh 250 to 340 grams, and males and females are the same size. The tail is nearly as long as the body and is thick with fur. The squirrel uses it to balance during a jump, wraps it round itself when asleep, and waves it in social displays. Long tufts of hair grow on the tips of the ears.

The name promises a red coat, but the back can be red, chestnut, brown, grey, black or even bluish. Animal Diversity Web says this species shows more coat variation than almost any other mammal of the region. Red coats dominate in Britain, while black animals are common on the continent and in mountain and northern forests. Whatever the colour of the back, the belly is white or cream. The squirrel moults twice a year. Between August and November it grows a thicker, darker winter coat with much longer ear tufts.

Habitat and range

The red squirrel ranges across the forested parts of Eurasia, from Iberia and Britain east to Kamchatka and Sakhalin. In the south it reaches the Mediterranean and Black Seas, northern Mongolia, Korea and north-east China. One subspecies lives on Hokkaido in Japan. People have also introduced it to Crimea, the Caucasus, parts of Central Asia and Tokyo. GBIF holds records from 71 countries, though that count includes zoo animals and escapes.

The species lives in both conifer forest and broadleaf woodland, from sea level up to the tree line in the mountains. Numbers are highest in large blocks of conifer forest, especially Scots pine, Norway spruce and Siberian pine. In western and southern Europe it uses mixed broadleaf woods, where a range of trees gives food all year. It also lives in parks, suburbs and conifer plantations, usually at lower density. It is scarce where forest is broken into small patches.

Diet and feeding

Tree seeds make up most of the diet, above all the seeds of conifers. A squirrel strips a cone scale by scale to reach the seeds inside, and leaves a chewed core behind. It also eats hazelnuts, acorns and beech mast, and opens a nut with its lower front teeth in a few seconds. Fruit, berries, fungi, lichen, buds, shoots, flowers and tree sap fill out the menu. Now and then it takes insects, bird eggs or nestlings. A Swedish study found bird remains in only four of 600 stomachs.

Food intake changes with the season, from about 80 grams a day in spring to 35 g a day in winter. In autumn the squirrel stores surplus food for the cold months. It buries nuts and cones in the soil or tucks them into holes and forks in trees. It finds these stores again by memory and smell, though its memory is weaker than that of the grey squirrel. Stores that are never recovered can sprout into new trees.

Behaviour and social life

The red squirrel is active by day. It starts at sunrise, works hardest in the morning and late afternoon, and rests in its nest around midday in summer. Between 60% and 80% of its active time goes on finding and eating food. It does not hibernate. In a storm or a hard frost it may stay in the nest for several days and live on its stores.

It builds a domed nest, called a drey, from twigs in the fork of a branch. A drey is about 25 to 30 centimetres across, and the squirrel lines it with moss, dry leaves, grass and strips of bark. Most dreys sit at least six metres up, close to the trunk. Tree hollows and old woodpecker holes serve as well. Each squirrel keeps several nests and moves between them on successive nights.

Red squirrels live alone and do not like to share food. In winter, though, several adults may sleep together in one drey for warmth. Older and larger animals dominate younger ones, and dominant males hold the largest home ranges. Home ranges overlap at the edges, and Animal Diversity Web says the species is not strongly territorial. On the ground it moves in bounds and stops often to sit up and sniff the air. In the trees it can leap between crowns up to four metres apart and always climbs down head first.

Communication and senses

The red squirrel has sharp eyesight, a keen nose and good hearing. It leaves scent on trees by rubbing glands on its face against the bark at regular spots. Urine carries the same message. These marks tell other squirrels who lives there, how high they rank, and whether they are ready to breed.

A squirrel that meets a rival calls loudly, stamps its feet and flicks its tail. If neither backs down, a fast chase follows, and the loser may get its tail bitten. Alarm calls warn other squirrels of a hawk or a cat. Between a mother and her kits, touch is also part of communication.

Reproduction and life cycle

Mating takes place in late winter, in February and March, and again in summer, in June and July. A female is in oestrus for a single day. Males follow her scent, and up to ten may chase her through the trees. The largest male usually wins and mates first, but the female often mates with others afterwards. Males take no part in raising the young.

Pregnancy lasts 38 to 39 days. A female can raise two litters a year, and a litter averages about three kits, though ten is possible. Kits are born blind, deaf and naked, and weigh 10 to 15 grams. Fur covers the body by 21 days, and the eyes open at about 30 days. Their first trip outside the nest comes at six to seven weeks, and weaning is complete by 8 to 12 weeks. After weaning they leave the area where they were born.

Young squirrels reach adult size at one year and most breed for the first time at 11 months or later. Life is short. Between 75% and 85% of kits die in their first winter, and about half of the adults die each winter after that. Most adults live 2 to 4 years, and 7 years is a record in the wild. One captive squirrel lived 14.8 years.

Predators and threats

The pine marten is the main mammal predator, because it can follow a squirrel through the branches. The Eurasian goshawk, the common buzzard and owls take squirrels from the canopy. On the ground, the red fox, the European wildcat and domestic cats and dogs all catch them. In suburbs the domestic cat is the chief killer. Stoats and climbing snakes raid nests for kits.

The biggest threat in Britain, Ireland and Italy is the eastern grey squirrel. The two species do not fight. Instead, the grey squirrel carries the squirrel parapoxvirus, which does not harm it but usually kills a red squirrel. At Formby in England, the disease cut the red population by 80% before 2008. The grey squirrel also digests acorns better, lives at higher density in broadleaf woods, and robs red squirrel food stores. Loss and fragmentation of forest threaten red squirrels across much of their range.

Population and conservation

The IUCN lists the red squirrel as Least Concern, but the global trend is downward. Regional lists rate it Near Threatened in Mongolia and Croatia and Vulnerable in Poland and China. The Bern Convention protects it in most of Europe, but in parts of Russia and Mongolia it is still hunted for fur. The British subspecies is in critical decline. Fewer than 160,000 remain in the UK, and about 120,000 of those are in Scotland.

British conservation rests on removing grey squirrels from places where reds survive. On Anglesey, grey squirrel control began in 1998, and the island now holds the largest red population in Wales. Brownsea Island and the Isle of Wight have only red squirrels, and islanders report any grey they see. Where the pine marten has spread back into England and Scotland, grey squirrels retreat, because greys spend more time on the ground. A government project now tests an oral contraceptive for grey squirrels, given from feeders that reds cannot open.

Relationship with humans

People have hunted the red squirrel for meat and fur for centuries. In the Middle Ages its pelt was a valued trade good across Europe. One study suggests the fur trade may have carried leprosy into medieval England, because the same strain occurs in squirrels on Brownsea Island today. In parts of the former Soviet Union the thick winter pelt is still sold.

In towns the red squirrel is a welcome sight, and volunteers across Britain count it and defend it. Foresters are less fond of it. It strips bark to reach the sap layer beneath, which slows tree growth and can damage a conifer plantation. Gardeners lose bulbs, flowers and vegetables to it, and it can be a noisy lodger in a roof. In Britain it is illegal to kill a red squirrel or to release a captured grey one. New Zealand bans its import as a prohibited new organism.

In culture and myth

In Norse tradition a squirrel called Ratatoskr races along the trunk of Yggdrasil, the world tree. It ferries gossip and abuse from the eagle in the crown down to the serpent Nidhogg among the roots. Scandinavian artists usually draw Ratatoskr as a red squirrel. Denmark has made the red squirrel its national mammal.

Medieval bestiaries used the squirrel as a symbol of thrift, because it stores nuts for winter. Later Christian writers turned that image around and linked the red coat and restless habits with the devil. In heraldry a squirrel is shown sitting upright with a nut in its paws. In some languages the phrase squirrel pelt is still a slang word for money, a memory of the fur trade. Modern spirit-animal writers read the red squirrel as a sign of energy and preparation, but that is probably a recent invention.