Family SCIURIDAE
Introduction
Squirrels are distinguished from the only other Australian rodent family, the Muridae, by their external form, in particular a tail bushy to the base and by skull differences, notably the presence of premolar teeth and a pronounced supra-orbital spine (Watts & Aslin 1981). The skull is broad and the eyes are large and well separated. Globably there are some 260 species, found in all regions except Madagascar and southern South America. The family is represented in Australia by two introduced species, Sciurus carolinensis Gmelin, 1788 and Funambulus pennantii Wroughton, 1905.
Both species are essentially herbivores, but their diet includes some animal material. In its native North American forests and in Great Britain, Sciurus carolinensis feeds predominantly on acorns and nuts favouring hickory nuts, but utilising a wide range including pecan, walnut, hazel and beech. In spring, buds and flowers, especially pollen-rich male flowers of hardwoods, are eaten. Berries, fungi and bark are included in the diet and browse may be taken when food is scarce. In Great Britain, these squirrels strip the bark of trees, apparently in the search for sweet sap, particularly in plantations of beech and sycamore. They can cause considerable damage. Their numbers are controlled by shooting or poisoning.
In India and Pakistan, Funambulus pennantii is a common and widespread commensal, found in homes, gardens and roadside trees. It is completely diurnal and generally arboreal. In particularly arid parts of its range, thick foliage and the moist microclimate of trees, particularly in orchards, provide shelter from excessive climatic conditions.
In the desert biome of northwest India it is found most frequently in rocky and ruderal areas but it is uncommon. In Australia, it has not adapted to natural environments and is restricted to suburban and/or plantation areas close to the original release sites. In Perth, the population still occupies an area of only about 30 km2; in Sydney the area occupied was smaller. Funambulus pennantii shelters in introduced trees or buildings and 'natural' food availability is limiting. At Como High School, Perth, the population of F. pennantii decreased during school vacations when additional food was unavailable. The population density of F. pennantii was highest in areas of Perth Zoo that had the highest density of fruiting trees and nest trees and that were closest to a supply of supplementary food.
Predation in the wild is apparently low (varanid lizards are reported predators). In Australia, introduced mammalian predators do not seem to be a major problem, but corvids and diurnal raptors harass squirrels. Predation of Funambulus is by captive hawks and brolgas at the Zoo and by rats, cats and Nankeen Night-herons. Perhaps the greatest predation was by man; active population culling by Zoo staff is used to limit populations and there may be some mortality during and consequent upon annual pruning of palm trees. Road casualties are another human-based cause of mortality.
The native habitat of Sciurus carolinensis is dense hardwood forests, particularly those of oak, hickory and walnut, but in Australia the species was found only in suburban parks and gardens. It never became established in natural forest and healthy populations seemed to depend on being fed by humans. In North America, the species encounters some competition from the Fox Squirrel, Sciurus niger. In the United Kingdom, S. carolinensis has been implicated with a dramatic reduction in range of the European Red Squirrel, Sciurus vulgaris.
The flea, Orchopeas howardi, is specific to Sciurus carolinensis with which it was introduced to England, but is not recorded from Australia, although other fleas, mites and lice have been reported. Viruses (foot and mouth disease, leptospirosis, mange), coccidiosis and shock disease are reported for S. carolinensis.
Economic Significance
Neither species has economic significance in Australia, except by causing minor damage to garden plants and as a tourist attraction (Funambulus in Perth Zoo, formerly at Taronga Zoo, Sciurus formerly at Ballarat Gardens). Funambulus pennantii is considered a potential pest species in Western Australia and has been a Declared Animal (Vermin) in that State since 1973. A few Funambulus, inadvertently translocated, have been found (and destroyed) in remote areas, as far as 140 km from Perth. Funambulus pennantii is a common commensal in northern India, but does not seem to be a major problem. In the United States, Sciurus carolinensis is the third most important game animal, with millions being taken annually for meat and pelts. In the United Kingdom, S. carolinensis is declared vermin because of its damage to forests (particularly hardwood plantations) and its presumed replacement of the indigenous S. vulgaris.
There is a potential pet trade in Funambulus pennantii and because of the zoo population in Melbourne, there is a possibility a feral population might be established there.
General References
Walton, D.W. & Richardson, B.J. (eds) 1989. Fauna of Australia. Mammalia. Canberra : Australian Government Publishing Service Vol. 1B 827 pp.
Watts, C.H.S. & Aslin, H.J. 1981. The Rodents of Australia. Sydney : Angus & Robertson xii 321 pp. 16 pls