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Common NameEastern Gray Squirrel, black squirrel, Carolina gray squirrel, cat squirrel, migratory squirrel, timber squirrel, silvertail - The word squirrel is etymologically derived directly from the Latin word for squirrel, sciurus.

Scientific NameSciurus carolinensis - The generic name is derived from the Greek words skia, meaning shadow, and oura, meaning tail, combined as skiouros which became sciurus in Latin. Carolinensis is a Latinized form of Carolina.

 

The Eastern Gray Squirrel is indigenous to North America east of the Mississippi River, though it has emigrated outside this range and has been introduced into the West and Canada.  It was introduced into Great Britain in 1876 at Woburn Abbey in Bedfordshire and other places and has since spread throughout the British Isles, displacing the native red squirrel.  From Great Britain, the "grey" squirrel made its way into Italy and other European countries and was introduced into South Africa by Cecil Rhodes, where it has thrived, and into Australia, where it has not.

 

The gray squirrel gets its name from the color of its fur, which ranges from grizzled dark to pale gray. The so-called black squirrel is also a gray squirrel, with melanism accounting for the darker appearance, the darker color being more common in northern ranges; it has been shown that the black animals have 18 percent less heat loss at -10 degrees C and a 20% lower basal metabolic rate. The pelage (coat) of the gray squirrel has an inner layer of short fur for warmth and an outer layer of "guard hairs" that protect the fur; the long hairs on the tail are the basis for the common name silvertail.

 

The tail is an important appendage, as it is used as a shield when fighting, as a blanket when cold and as a shade when hot, the latter providing the basis for the name for the squirrel in Greek: skia oura meaning shadow tail.  The tail is also used as a means of communication, signaling anger, excitement, fear or curiosity. It has striped coloration on young squirrels, becoming a single solid color at maturity.  Most importantly, the tail is a means of steering and balancing when running and jumping between branches in trees.

 

Gray squirrels are well adapted to their arboreal habitat. They have excellent vision that is accentuated by the depth perception that the parallax of their eyes enables. Their strong legs are capable of leaps in excess of eighteen feet at treetop elevations. They can ascend and descend a tree trunk of any girth, as the sharp rear claws dig into the bark in any direction, the back legs being capable of a rotation of one hundred and eighty degrees. If they fall, their tails provide parachute-like air resistance to slow their descent.

 

As squirrels spend most of their time in trees, they have evolved three different types of dwellings: winter and summer drays and dens.  Drays are made out of leaves and other forest detritus. The winter dray is a robust affair constructed of branches and leaves located in the main fork of a tree high enough to evade terrestrial predators but low enough to escape the ravages of severe weather. The summer dray is generally a more flimsy affair and may be only a platform of leaves about thirty feet off the ground. The den is the most secure of the three, consisting of a hole about three inches across leading to a cavity at least twelve inches deep in a mature tree with decaying heartwood.  The drays and dens are normally collocated in the same stand of trees to allow movement among them according to food supplies and predators. One can approximate the number of squirrels in the area by tallying two squirrels for every three nests.  Since squirrels get adequate hydration from the foods they eat, they do not need to descend from the trees to drink, minimizing their exposure to predators.

 

Squirrels are not dimorphic; both sexes are the same size and have the same coloration.  Males compete against each other to mate with the females, a process that involves a chase that ends when the female decides to accede to the emotive male; copulation lasts less than thirty seconds. Breeding occurs between December and February and again from May to June, the female producing one litter of 2 to 4 young in late winter (sheltering in the den) and a second litter in midsummer (sheltering in the dray). The young are raised solely by the female; the worst fights among normally playful and docile squirrels occur when males approach the nests of lactating females. After the mating season, the testicles of the male squirrels shrink in size from seven grams to one gram so they look like they have been castrated.  This is the genesis of the myth that the more aggressive red squirrels castrate the more prolific gray squirrels.

 

Gray squirrels have a very high metabolism, maintaining a body temperature of about 101 degrees F.  To do this, they need to eat about their own weight in food every week. During the late summer and fall, they consume about a third more than required for sustenance to fatten up for the winter. They preferentially feed on the nuts, flowers and buds of oak, hickory, pecan, walnut and beech trees. However, squirrels move extensively around their home ranges according to the availability of food, generally consuming only one type of food at a time. Their diet extends to a wide variety of trees and flowers, including the seeds and catkins of gymnosperms such as cedar, hemlock and pine.  They are omnivorous and they will eat insects, bones, bird eggs, fledglings, frogs, and fungi (as in the picture above).

 

One of the more notable aspects of the behavior of the gray squirrel is the practice of "scatter hoarding."  Unlike most other small mammals, the gray squirrel does not store food in a centralized location like the den or the dray. Rather, food is stored in the form of buried nuts, not in the location where they are found, but in remote, shallow, individual holes dug with the forefeet and covered with dirt to a depth of about inch below the surface. One postulated reason for this behavioral anomaly is that it prevents competing animals from raiding their food supply. It has been observed that they will consciously conceal their activities from other squirrels, to the extent that burials will be faked by carrying out the motions without actually caching the nut.

 

During the winter, squirrels are most active about 2 hours before dawn and two hours before dusk, engaged mostly in the recovery of nuts. There is some scientific controversy concerning the degree to which squirrels remember the location of the nuts they bury versus serendipity with possible sensual directivity.  In one study, scientists buried nuts independently of the squirrels in the same area where they had buried their own. Both varieties were located and removed by the squirrels with approximately equal likelihood, with an overall recovery rate of about 85 percent. However, it is the predominant belief that they use a combination of memory and smell to locate buried nuts. This is supported by the observation that squirrels will burrow under deep snow in order to get within olfactory range of the buried food.

 

An interesting aspect of the scatter hoarding behavior is the relationship between gray squirrels and oak trees. There are two groups of oak trees, red oaks with high fat and high tannin acorns (and leaves with pointed lobes) and white oaks, which are lower in fat and tannin (with round-lobed leaves).  Red oak acorns remain dormant throughout the winter whereas white oak acorns germinate almost immediately. Accordingly, squirrels store red oak acorns and eat white oak acorns. Alternatively, they may store a white oak acorn, but only after biting off the end of the nut that contains the embryo to prevent germination.  .

 

Large mass movements of gray squirrels have been observed historically to occur in September. These movements are known as emigrations vice migrations, as the squirrels permanently move to new environs.  In the early colonial period, when the eastern forests were more extensive, this behavior was much more prevalent. In the 1840's John Audobon noted the "wandering habits and  singular and long migrations" of squirrels and believed they were a different species which he named S. migratorius whence the common name migratory squirrel derives. As emigrations occur in September when food is plentiful, questions arise concerning causation.  The predominant theory is that variances in oak tree acorn production, known as masting, create surges in the squirrel population that become manifest as the more numerous squirrels begin searching for nuts to bury for the winter the year following the mast year, when few acorns are produced. When they find the paucity of nuts, they instinctively "emigrate" to a more bountiful area.