Sciurus carolinensis (Grey Squirrel)

Life > Eukaryotes > Opisthokonta > Metazoa (animals) > Bilateria > Deuterostomia > Chordata > Craniata > Vertebrata (vertebrates)  > Gnathostomata (jawed vertebrates) > Teleostomi (teleost fish) > Osteichthyes (bony fish) > Class: Sarcopterygii (lobe-finned fish) > Stegocephalia (terrestrial vertebrates) > Reptiliomorpha > Amniota > Synapsida (mammal-like reptiles) > Therapsida > Theriodontia >  Cynodontia > Mammalia (mammals) > Placentalia (placental mammals) > Euarchontaglires > Glires > Rodentia (rodents) > Sciurognathi > Family: Sciuridae (squirrels)

Sciurus carolinensis, Company Gardens, Cape Town, South Africa. [photo H.G. Robertson, Iziko ©]

Indigenous to North America and introduced by Cecil John Rhodes to Cape Town around the turn of the 19th-20th Century. Grey squirrels are common in the Western Cape wherever there are pines and oaks and has not spread significantly into natural vegetation. Hence, while alien to South Africa, it is not considered a serious threat to local biodiversity although it does supplement its vegetarian diet by predation of eggs and chicks in bird's nests. 

Identification

Squirrels are easily recognized with their cylindrical bodies and bushy tails. They show a marked difference in coat colour in winter and summer. The summer coat is generally a brownish-grey, while the winter coat is a silver-grey. The underparts are white or just off-white. Their bushy tails have several uses; they serve for balance while running, as a rudder when jumping, as a signal flag when communicating and as a blanket that they wrap around for warmth when sleeping. The eyes are large surrounded by a light white or off-white coloured ring. Placed on the sides of the head they give the squirrel a wide field of vision. There are touch sensitive whiskers (vibrissae) on the head, feet, and the outsides of the legs. Squirrels are extremely agile when moving through the trees and have prehensile limbs and long sharp claws for gripping. Their incisors grow continuously and are worn back down with use. Although not common white albinos and melanistic black forms also occur in some populations.

Size

Total Length 50 cm; weight 600g '

Dental formula

 I C P M = 22

Distribution and habitat

Native to the hardwood forests of North America, the Grey squirrel was introduced into South Africa by Cecil John Rhodes. At the turn of the 19th century he released squirrels on Groote Schuur estate in Cape Town. By the 1970’s their range had extended as far as Swellendam in the Western Cape. Their distribution is patchy and discontinuous being closely associated with oak trees and pine plantations, and expands and contracts with the establishment and removal of the trees. They are also found in vineyards and deciduous fruit orchards where pine trees have been planted as windbreaks. Readily available water is also an important requirement. Grey squirrels are unable to utilize fynbos vegetation, and this serves to buffer its spread. Most of the indigenous trees do not bear fruit or berries suitable for their food requirements. To date their range remains confined to the south-western Cape and in most cases the squirrels will only expand their range by introduction new plantations.Restricted to pine and oak plantations, as well as suburban gardens in the south-western Cape. Natural distribution is North America.

General Behaviour

Grey squirrels are solitary, except when a female is accompanied by her young. They are diurnal and may be seen at anytime of the day but are generally most active in the early morning and later in the afternoon. Although it is an arboreal (tree dwelling) species, squirrels spend a lot of time foraging on the ground. They rest in dreys, a spherical nest, constructed in the branches of the trees. These nests are normally about the size of a soccer ball and made up of twigs, shredded bark, leaves and any other soft materials such as string, paper and rags. It is thickly lined with dry grass, moss and fur and is very well insulated. Squirrels will also make use of tree holes that they line with leaves and other soft litter. Tree squirrels do not hibernate, however, in cold weather they will stay in their nests only leaving every few days when it is necessary to find food.

When threatened the individual will flatten its body on the side of the tree trunk away from the threat and remain completely still until it is safe to move again. The alarm call is a rapid scolding “kuk-kuk-kuk”.

Food

Squirrels are primarily vegetarian, with acorns and pine seeds making up most of their diet. When unavailable they will eat other nuts and seeds as well as fruit, young shoots and buds, and flowers. They will also eat insects, fungi, bird’s eggs, nestlings and small vertebrates if they are available. Grey squirrels hoard acorns, pine nuts and other seeds by burying them safely in the soil. Squirrels will poach nuts from another’s larder, this leads to squirrels bury hundreds of nuts in a season and scattering their stores. Many seeds are never retrieved and results in inadvertent tree-seed dispersal and squirrels acting as inadvertent reforesters. This long co-evolution of tree-squirrels with many of the forest tree species, has resulted in these trees producing such abundant crops of nuts that many buried nuts are never recovered and are left to germinate.

Reproduction

The gestation period is about 45 days. The young are born in the Western Cape during two main periods spring (August/November) and summer (December/February). The average litter size of the gray squirrel is 3. The young are born naked and blind and only open their eyes at about 4 weeks old. Fur begins to appear after about 2 weeks and the young will remain in the nest until they are 5 – 6 weeks old. Weaning starts at about 7 weeks and is completed by the time the young are 10 weeks old. The adult size is reached at about 9 months. Females may have 2 litters annually.

Life span

6-7 years.

Conservation

Other than its introduction to the Cape Peninsula, the Grey squirrel has also been introduced in the UK and Europe. In the UK and Northern Italy the indigenous Red squirrel is listed as near threatened due to exclusion by the Grey squirrel. While it is regarded as an invasive alien in South Africa, the Grey squirrel is currently not problematic as its distribution is limited to commercial plantations and urban gardens. The Grey squirrels along the Oak-lined Government Avenue in Cape Town are a major tourist attraction and hardly a minute goes by in the day without someone photographing one of them.

Text by Denise Hamerton