Western Grey Squirrels (Sciurus griseus) are also known as California
Grey Squirrels, and are the only large grey tree squirrel in their range on the
Western Coast of the United States. Western Grey Squirrels are found in the
Pacific States from Washington to California.
Western grey squirrels are medium sized tree or arboreal squirrels. They have grey backs with numerous white tipped hairs and a white belly. The backs of their ears are reddish-brown and they have long bushy tails with bands of grey white and black, especially below.
The life span of Western grey squirrels is equivalent to that of Eastern grey squirrels; 7 - 8 years in the wild. Their bodies measure 450 - 600 mm total length, 240 - 310 mm tail length, 75 - 100 mm right hind foot, and they range in weight from 350 - 950 grams. Western grey squirrels have both a summer and winter coat, and therefore molt twice each year. The spring molt begins in May or June and the autumn molt begins in September, but the tail only molts once each year in the summer.
Western grey squirrels have four sets of whiskers located above and below the eyes, on the underside of the head in front of the throat, and on the nose. Whiskers, also known as vibrissae are touch receptors that provide the animal with information about its immediate surroundings. Western grey squirrels have very good eyesight even in dim light, and a wide field of vision. They also have a well developed sense of smell and hearing.
Squirrels have upper and lower incisor teeth followed by a gap called a diastema. The diastema is where the canine teeth would normally be found in carnivorous animals such as cats or dogs, or omnivorous animals such as monkeys. Behind the diastema are the cheek or grinding teeth which consist of premolars and molars. As with other rodent species, the incisors continuously grow to compensate for the enormous amount of wear that comes from a herbivorous diet. Young squirrels have milk teeth which are replaced by permanent teeth when they are between six and twelve months old.
Western grey squirrels are highly adapted for climbing trees and fatal falls are rare. Adaptations for climbing trees include tough curved claws, and the ability to leap considerable distances using powerful hindlimbs. Tails are used for balance when running and leaping between trees, and held over the back of a resting animal.
Juvenile squirrels are born without hair and weigh between 13 and 18 grams. Hair begins to grow on the tail and dorsum by 21 days, and on their ventrum by 42 days. Eyes open at 24 - 42 days, ears at 21 - 28 days, lower incisors erupt at 19 - 21 days, upper incisors in week 4 and cheek teeth in week 6. Weaning begins at 7 weeks and is complete by 10 weeks. Adult body mass is reached after 8 - 9 months.
Western grey squirrels are non-territorial. They have small overlapping home ranges which average 3 hectares in size, but can vary from 0.5 hectares to greater than 7 hectares. There is little difference in home range size between males and females, although males having slightly larger home ranges than females. For most arboreal squirrel species, home range size is negatively correlated with food supply and squirrel population density.
Western Grey squirrels are generalist feeders. They rely on pine cones, acorns and other nuts, some fungi, berries and occaisionally insects. Food consumption peaks in summer or autumn and decreases in winter. Autumn rates of food consumption exceed energetic needs by 32% so that the animals can increase their weight before the onset of winter. Western grey squirrels are classic scatterhoarders. They carry nuts in their jaws and bury them in various locations within their home ranges. Olfaction and memory are used in locating their caches.
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