Red squirrel

The red squirrel, also called Eurasian red squirrel, is a species of tree squirrel in the genus Sciurus. It is an arboreal and primarily herbivorous rodent and common throughout Eurasia.

Taxonomy

There have been over 40 described subspecies of the red squirrel, but the taxonomic status of some of these is uncertain. A study published in 1971 recognises 16 subspecies and has served as a basis for subsequent taxonomic work. Although the validity of some subspecies is labelled with uncertainty because of the large variation in red squirrels even within a single region, others are relatively distinctive and one of these, S. v. meridionalis of South Italy, was elevated to species status as the Calabrian black squirrel in 2017. At present, there are 23 recognized subspecies of the red squirrel. Genetic studies indicate that another, S. v. hoffmanni of Sierra Espuña in southeast Spain, deserves recognition as distinct.

S. v. alpinus. Desmarest, 1822.
S. v. altaicus. Serebrennikov, 1928.
S. v. anadyrensis. Ognev, 1929.
S. v. arcticus. Trouessart, 1906.
S. v. balcanicus. Heinrich, 1936.
S. v. chiliensis. Sowerby, 1921.
S. v. cinerea. Hermann, 1804.
S. v. dulkeiti. Ognev, 1929.
S. v. exalbidus. Pallas, 1778.
S. v. fedjushini. Ognev, 1935.
S. v. formosovi. Ognev, 1935.
S. v. fuscoater. Altum, 1876.
S. v. fusconigricans. Dvigubsky, 1804
S. v. leucourus. Kerr, 1792.
S. v. lilaeus. Miller, 1907.
S. v. mantchuricus. Thomas, 1909.
S. v. martensi. Matschie, 1901.
S. v. ognevi. Migulin, 1928.
S. v. orientis. Thomas, 1906. Ezo Red Squirrel.
S. v. rupestris. Thomas, 1907
S. v. ukrainicus. Migulin, 1928.
S. v. varius. Gmelin, 1789.
S. v. vulgaris. Linnaeus, 1758.
Description

The red squirrel has a typical head-and-body length of, a tail length of, and a mass of. Males and females are the same size.
The long tail helps the squirrel to balance and steer when jumping from tree to tree and running along branches and may keep the animal warm during sleep.
The coat of the red squirrel varies in colour with time of year and location. There are several coat colour morphs ranging from black to red. Red coats are most common in Great Britain; in other parts of Europe and Asia different coat colours coexist within populations, much like hair colour in some human populations. The underside of the squirrel is always white-cream in colour. The red squirrel sheds its coat twice a year, switching from a thinner summer coat to a thicker, darker winter coat with noticeably larger ear-tufts between August and November. A lighter, redder overall coat colour, along with the ear-tufts in adults and smaller size, distinguish the red squirrel from the eastern grey squirrel.

Distribution and habitat

Red squirrels occupy boreal, coniferous woods in northern Europe and Siberia, preferring Scots pine, Norway spruce and Siberian pine. In western and southern Europe they are found in broad-leaved woods where the mixture of tree and shrub species provides a better year-round source of food. In most of the British Isles and in Italy, broad-leaved woodlands are now less suitable due to the better competitive feeding strategy of introduced grey squirrels.
In Great Britain, Ireland and in Italy, red squirrel populations have decreased in recent years. This decline is associated with the introduction by humans of the eastern grey squirrel from North America. However, the population in Scotland is stabilising due to conservation efforts.

Ecology and behaviour

The red squirrel is found in both coniferous forest and temperate broadleaf woodlands. The squirrel makes a drey out of twigs in a branch-fork, forming a domed structure about in diameter. This is lined with moss, leaves, grass and bark. Tree hollows and woodpecker holes are also used. The red squirrel is a solitary animal and is shy and reluctant to share food with others. However, outside the breeding season and particularly in winter, several red squirrels may share a drey to keep warm. Social organization is based on dominance hierarchies within and between sexes; although males are not necessarily dominant to females, the dominant animals tend to be larger and older than subordinate animals, and dominant males tend to have larger home ranges than subordinate males or females.
The red squirrel eats mostly the seeds of trees, neatly stripping conifer cones to get at the seeds within, fungi, nuts, berries, vegetables, garden flowers, tree sap and young shoots.
More rarely, red squirrels may also eat bird eggs or nestlings. A Swedish study shows that out of 600 stomach contents of red squirrels examined, only 4 contained remnants of birds or eggs.
Excess food is put into caches called "middens", either buried or in nooks or holes in trees, and eaten when food is scarce. Although the red squirrel remembers where it created caches at a better-than-chance level, its spatial memory is substantially less accurate and durable than that of grey squirrels.
Between 60% and 80% of its active period may be spent foraging and feeding. The red squirrel exhibits a diurnal activity pattern. Though during summer it can often rest in its nest in the middle of the day, avoiding the heat and the high visibility to birds of prey that are dangers during these hours. During the winter, this mid-day rest is often much briefer, or absent entirely, although harsh weather may cause the animal to stay in its nest for days at a time.
No territories are claimed between the red squirrels and the feeding areas of individuals overlap considerably.

Reproduction

Mating occurs in late winter during February and March and in summer between June and July. Up to two litters a year per female are possible. Each litter averages three young, called kits. Gestation is about 38 to 39 days. The young are looked after by the mother alone and are born helpless, blind, and deaf. They weigh between 10 and 15g. Their body is covered by hair at 21 days, their eyes and ears open after three to four weeks, and they develop all their teeth by 42 days. Juvenile red squirrels can eat solids around 40 days following birth and from that point can leave the nest on their own to find food; however, they still suckle from their mother until weaning occurs at 8 to 10 weeks.
During mating, males detect females that are in oestrus by an odour that they produce, and although there is no courtship, the male will chase the female for up to an hour prior to mating. Usually, several males will chase a single female until the dominant male, usually the largest in the group, mates with the female. Males and females will mate several times with many partners. Females must reach a minimum body mass before they enter oestrus, and heavy females on average produce more young. If food is scarce breeding may be delayed. Typically a female will produce her first litter in her second year.

Life expectancy

Red squirrels that survive their first winter have a life expectancy of 3 years. Individuals may reach 7 years of age, and 10 in captivity. Survival is positively related to the availability of autumn-winter tree seeds; on average, 75–85% of juveniles die during their first winter, and mortality is approximately 50% for winters following the first.

Competitors

Arboreal predators include small mammals such as the pine marten, wildcats and the stoat, which preys on nestlings; birds, including owls and raptors such as the goshawk and buzzards, may also take the red squirrel. The red fox, cats and dogs can prey upon the red squirrel when it is on the ground. Humans influence the population size and mortality of the red squirrel by destroying or altering habitats, by causing road casualties, and by introducing non-native populations of the North American eastern grey squirrels.
The eastern grey squirrel and the red squirrel are not directly antagonistic, and violent conflict between these species is not a factor in the decline in red squirrel populations. However, the eastern grey squirrel appears to be able to decrease the red squirrel population for several reasons:

The eastern grey squirrel carries a disease, the squirrel parapoxvirus, that does not appear to affect their own health but will often kill the red squirrel. It was revealed in 2008 that the numbers of red squirrels at Formby had declined by 80% as a result of this disease, though the population is now recovering.
The eastern grey squirrel can better digest acorns, while the red squirrel cannot access the proteins and fats in acorns as easily.
When the red squirrel is put under pressure, it will not breed as often.

In the UK, due to the above circumstances, the population has today fallen to 160,000 red squirrels or fewer; 120,000 of these are in Scotland. Outside the UK and Ireland, the impact of competition from the eastern grey squirrel has been observed in Piedmont, Italy, where two pairs escaped from captivity in 1948. A significant drop in red squirrel populations in the area has been observed since 1970, and it is feared that the eastern grey squirrel may expand into the rest of Europe.

Conservation

The red squirrel is protected in most of Europe, as it is listed in Appendix III of the Bern Convention; it is listed as being of least concern on the IUCN Red List. However, in some areas it is abundant and is hunted for its fur.
Although not thought to be under any threat worldwide, the red squirrel has nevertheless drastically reduced in number in the United Kingdom; especially after the eastern grey squirrel was introduced from North America in the 1870s. Fewer than 140,000 individuals are thought to be left in 2013; approximately 85% of which are in Scotland, with the Isle of Wight being the largest haven in England. A local charity, the Wight Squirrel Project, supports red squirrel conservation on the island, and islanders are actively recommended to report any invasive greys. The population decrease in Britain is often ascribed to the introduction of the eastern grey squirrel from North America, but the loss and fragmentation of its native woodland habitat have also played a significant role.
In contrast, the red squirrel may present a threat if introduced to regions outside its native range. It is classed as a "prohibited new organism" under New Zealand's Hazardous Substances and New Organisms Act 1996 preventing it from being imported into the country.