Sciurus carolinensis – (Eastern) Grey Squirrel

In winter, in the northern parts of their range, they shelter in tree holes and tree crevices, insulated with leaves and other soft materials. Otherwise, they will nest in “outdoor” spherical leaf nests, 12” to 19” in diameter. These loose, leafy nests are built high up in mature deciduous trees, with the main entrance near the tree’s trunk. To discover where a squirrel may be nesting, follow one who is carrying leaves, twigs and/or shredded bark.

Behaviour:
I don’t think of squirrels as migratory, so this story really piqued my curiosity: Legend has it that in the early 1800’s there was an intense grey squirrel migration, with up to a billion animals moving into new territory, swaths a mile wide. When encountering a river, to make their passage across, the squirrels would float on pieces of bark and hoist their tails up for sails! Today, surplus and scarcity of acorns in any given year may instigate mass migrations of Eastern Grey Squirrel.

S. carolinensis is diurnal, with their day starting at sunrise and ending just a little after sunset. The home range of each individual is fixed. Within this range he or she acquires food, gains protection and locates a place to den. Ideally, this range would be several wooded acres, more for males, less for females. Not territorial creatures, these home ranges overlap significantly. Defense is reserved for females during breeding season.

The social group, consisting of all squirrels with overlapping ranges, has a hierarchy of dominance based on age and sex, with older males at the top. With this hierarchy very little aggression occurs. If you witness aggression, it could be a young squirrel attempting to establish a home range near its birthplace and within that of an older squirrel. In this case, the local hierarchy is being redefined.

Aggression for dominant squirrels takes the form of tooth chattering, sometimes audible, and forward and back tail waving. General alarm is also displayed as tail waving. On the ground, dominant squirrels will also jump towards, run at or chase others, often resulting in the two, classically, spiraling up a tree.

Squirrels have highways in the trees, efficient routes that they use regularly. When they pause, sniff and rub the sides of their face on a limb, they may be leaving scent marks to keep track of one another.

Life Cycle:
Mating/breeding occurs from December to February and again from June to July. The mating ritual begins with a pre-chase, the male following the female (who is giving off a scent) at a comfortable pace. The male will stop and sniff as he follows. Sometimes he gets close enough to sniff her directly. When the female is in full estrus the early morning mating chase begins. As many as ten males will chase a single female, all repeatedly calling “chuck”, among the trees. Females only mate on their home range, but males will travel out of their range at the sound of her chucks! There are occasional outbursts of aggression from both the female and among the males. One can determine who is who by the social hierarchy. In this case, the estrous female is in lead, followed by the older, most dominant males, with the younger males bringing up the rear.

Young are born in a tree den that is aggressively defended by the mother from all other squirrels, including the father. Gestation is 45 days, with an average of 3 young per litter. The infants are born hairless, with eyes and ears closed. As mammals, they gain their nourishment from mother’s milk. Four to five weeks after birth they make short trips out of the den, fully furred, with eyes and ears open. Weaning occurs at 8-9 weeks old and they are on their own when they disperse from their mother’s home range around 4 months of age.

Ecology:
One particularly heavy, cold winter I discovered many black-stained holes in stark-white snow under a large walnut tree. The holes did not extend into underground tunnels, but were only up to a foot deep and the size of a grey squirrel’s circumference. This is consistent with what I now read, that these squirrels do not store their food in large underground caches. Instead, they dig a shallow hole in the forest floor where they place and cover only one food item. They will also use tree cavities to store somewhat larger caches.

Apparently, Grey Squirrels are very adept at relocating their buried nuts. This may be due to scent marking the nut at the time of burial – pushing the nut down into the dug hole with their nose before covering it over with earth. The low percentage of “lost” nuts will germinate to become — seedlings … then saplings … join the understory … and finally reach the canopy as mature trees — a significant contribution to forest regeneration.

To protect their own hardwood community from an over-abundance of hungry squirrels, nut trees have evolved a sporadic crop pattern. Most years are lean, then once every 2-7 years all the trees throughout their range suddenly produce an abundance, referred to as a bumper or “mast year” crop. The lean years establish a low population of squirrels that then cannot make use of the abundance offered during the following mast year. I’ve been wondering what signals mast crops? Could it be the specific chemical levels injected into the soil by means of squirrel urine?

Threats:
Squirrels are often roadkill victims, especially the young ones in search of a home range.
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When settlers first arrived on Turtle Island Grey Squirrel was so numerous as to be considered a significant threat to their agricultural crops. Some states declared a bounty on them, and this, along with the continuous and universal deforestation, caused such a drop in this species’ population there arose concern that Sciurus carolinensis would become extinct! With grey squirrel adaptation to urban environments, and with a decrease in farming, resulting in old field succession towards forest recovery, Eastern Grey squirrel has made a successful comeback.