Basic Life History
There are several species of tree squirrels (order Rodentia, family Sciuridae) native to the United States, but the most widely distributed are the Eastern Gray squirrel (Sciurus carolinensis) and the Fox squirrel (Sciurus niger). Other squirrels are the Western Gray squirrel, Red squirrel or Pine squirrel, Douglas squirrel, Southern Flying squirrel, Northern Flying squirrel, Alberts (or tassel-eared) squirrel and the Arizona Gray squirrel.
The squirrel most common in northern Virginia is the Sciurus carolinensis, the Eastern Gray squirrel. Sciurus is Greek for animal that sits in the shade of its own tail, carolinensis refers to the fact that the animal was first observed and named in the Carolinas.
Gray squirrels are definitely the most frequent wild friends visiting our backyards. On one hand, they are intelligent, inquisitive, very handsome and interesting to watch; on the other hand, to some people, they are destructive, aggressive, annoying and very persistent. Some even call them tree rats and, indeed, both squirrels and rats are members of the rodent family. Squirrels are diurnal, meaning daytime creatures. Regardless of how you feel about them, they are the most fascinating wild creatures that almost everyone can observe and enjoy.
The Eastern Gray squirrel is a handsome, slim and tree climbing animal, usually measuring 18-20 inches in length. About half of the animals length is its luxurious, bushy tail. The tail is used to balance, regulate body temperature, and as a signaling device. Two upper and two lower prominent, orange incisors characterize Gray squirrels, like all rodents. These teeth are rooted in the very back of the jaw, and are ever-growing
Adults usually weigh about 1 to 1-1/2 pounds. The sides and back of the animal are covered with hair banded with black and brown and tipped in white. The undersides of the squirrel are white, often tinted in brown or rust. The bushy tail is banded in black and brown and has a white tip. The overall appearance of the animal is salt and pepper. However, gray is not always gray! Gray squirrels can also be black and some pure white. Melanistic animals are more common than albinistic. A litter of gray squirrels may well also contain black squirrels.
Gray squirrels can have two litters a year, one in late winter and a second one in summer. Juvenile females less than nine months old virtually never enter breeding conditions in the year of their birth. Females 9-15 months old usually produce only one litter, but dominant adult females 2 years old and older reproduce at the beginning of the season, rear their offsprings and may produce a second litter. If food is scarce and crops are poor, fewer adults and even fewer yearlings produce young. When the female goes in heat, she is usually chased in hot pursuit up and down trees by often as many as a dozen males. After the female has conceived, she becomes solitary and very territorial, chasing off other squirrels from the area of her den. Squirrels prefer tree cavities as denning sites, but if these are not available, squirrels build leaf nests that are also called dreys. Squirrels also enjoy man-made nesting boxes. These boxes should be 18 to 28 inches high and about 12 inches square, with a 3-inch hole near the top of the front and a small drainage hole on the bottom of the box. They should be placed 20 to 30 feet above ground.
Gestation of the Eastern gray squirrel is between 40-45 days. The female gives birth to a litter of 2 to 4 youngsters. Newborns are about 4 ½ inches long and weigh only 15grams (½ ounce). They are pink, naked, except for little whiskers, and totally helpless. Their eyes and ears are sealed. After about a week of nursing, the babies can double in weight. After two weeks, some hair is grown and at one month, their ears open and the lower incisors appear through the gums. Their eyes finally open between 4 and 5 weeks. They are now fully furred and weigh between 3 to 4 ounces and measure about 10 inches overall, 4 ½ inches of which is the tail.
When 6 to 7 weeks old, they make the first unsteady attempt at moving around. At this time, they may venture to the edge of the nest and start to nibble on tender buds, leaves, and insects, or anything else they can reach.
When 2 months old, they are able to crack nuts and acorns. After the teeth emerge, the squirrel begins to eat hard objects, such as tree branches, nuts and other wood to satisfy the need to gnaw and keep the incisors worn down and chisel-sharp.
It is not unusual for squirrel mothers to build another nest after the one inhabited is becoming infested with fleas. She will carry the baby by grasping it at the belly with her mouth; the baby will wrap its feet around her neck and head for the ride to the new den. A squirrel mother is very attentive and a good mother in the nest. She nurses her babies for 9 10 weeks. She will not bring food to the nest like some bird mothers do. For the first few days that they leave the nest, the young are retrieved by the scruff of the neck. When 10 to 12 weeks old, baby squirrels are weaned and are able to fend for themselves, eating solid food. At this time, the mother squirrel is ready to breed again and is being chased by a dozen or so admirers and preparing another nest for the late litter that will be born in mid-July to August. She no longer has contact with her first litter. Female squirrels seem to develop quicker than males and leave the nest earlier. Even after juvenile squirrels are fully-grown, they are easy identified by a less luxurious tail.
The main or primary foods making up the bulk of the diet are tree seeds (acorn, pine or spruce cones, nuts) and fruit. Hickory nuts are their favorite even if its not energy efficient cracking the hard shells. Fallen acorns that are sprouting will have the embryo nipped out before being buried. Acorns that will sprout in the spring are just buried. Young squirrels appear to learn how to handle cones and seeds by trial and error, but the process improves if they are able to observe experienced squirrels handling these foods. Youngsters from the winter litter devour insects and greens and they use claws and teeth to remove pieces of bark to search for ants, beetles, spiders, and larvae. Insects are a great source of protein and squirrels consume as many as they can find.
In late summer, their diet begins to change and they begin caching nuts in the ground. They will dig nuts up after other food becomes scarce and will stop retrieving cached food as soon as fresh vegetation is available in early spring. Contrary to common belief, squirrels do not remember where they buried nuts. Studies show that they recover nuts by smell and not memory, and the nuts that are retrieved are not necessarily the nuts they buried. A squirrels sense of smell is very strong and it can sniff out a buried nut under a foot of snow.
Gray squirrels do not hibernate. However, during inclement weather, they may not leave their nest for several days. Males often den together to share body warmth. They can be inactive for two weeks, losing some weight, but not starving to death. Once they come out after the weather improves, they are ravenous and will very actively seek food. Birdfeeders are raided and even suet hanging in trees for woodpeckers and other birds is a great favorite. Squirrels also enjoy fungi, lichens, pinecones, fruit, berries, mushroom, corn and other grain. The squirrel may occasionally eat bird eggs and chew on bones and deer antlers for calcium, phosphorus and other minerals the animal may need. About 10 % of a squirrels diet is animal matter when available during the season.
The life span of the gray squirrel in the wild is one year, with 25 percent living longer. Most squirrels killed on roads are youngsters. Not yet street smart and eager to gather nuts and acorns in late summer and fall, they run across roads and get hit by cars. In captivity, gray squirrels have lived as long as 20 years. Biologically, they should have a life span of at least 12 years, but most dont live longer than 6 years if they survive the dangerous first year of their life. Squirrels have natural predators, such as hawks, owls, snakes, foxes, and bobcats. House cats also prey on young squirrels. In addition, accidents and parasites take a toll on some of the squirrels. Humans with cars as well as hunting and trapping cause many deaths in the squirrel population. However, a squirrels greatest danger is malnutrition. Not sufficient food kills the largest number of squirrels having made them susceptible to disease. Summer litter squirrels face a winter with less fat reserves and less food buried than squirrels born earlier in the year.
More on Squirrel Nests
There are three types of squirrel nests or dreys used by squirrels: winter dreys, summer dreys, and tree dens. While in the nest, squirrels roll up in a ball and use their tail as a cover.
Tree dens are holes or cavities in the main trunk of trees, which have been left by branches falling away or have been made by birds, such as woodpeckers. Some dens occur in dead trees, but most in live trees.
Both winter and summer dreys are conspicuous twig and leaf nests built in trees. They are usually built in the top fork of a tree or in the crotch of a limb near the trunk. Most nests are generally globular in shape, but may vary depending on the supporting base. A single entrance usually faces the main trunk or the nearest limb that provides access to the nest. They have to withstand high winds and inclement weather and have to be secure against predators.
The winter dreys are by far the most elaborate. The entrance to the drey is usually not noticeable. They are waterproof with the outer coarse layer of interwoven twigs, which the squirrels usually remove from the tree in which the drey is built. There is an inner lining consisting of moss, bark, leaves, fur, feathers, lichen and any man-made material they can find. Dreys used by females to rear young, tend to be very well padded. Winter dreys persist in trees for several months until they get blown apart.
Summer dreys are much simpler, mostly twigs and leaves on saucer shaped platforms on exposed branches on which squirrels rest during hot weather. Summer dreys usually fall apart quickly after squirrels abandon them.
Squirrels are very vocal creatures. Their barking, chattering, screaming, buzzing, mewing, purring and assorted chucks are part of squirrel talk. Also, the flushing and flickering of the tail, and stomping of the feet, the way they walk and raising hair on the bodies in conjunction with the vocalization is part of squirrel communication. There are several known calls. One announces the available food; a similar one is given by females in breeding. The alarm sound is the most common one we hear often when there is danger in the area. Usually, hawks or cats in the area are the cause.
Squirrels, like most mammals, tend to have many parasites including ticks, fleas, mites, lice, chiggers, tapeworm, threadworms, ringworm and mange. These can lead to disease, and in extreme cases, death. Another insect causing visible effects on squirrels is the bot fly, or warble fly. The adult flies lay their eggs in a squirrel nest. After hatching, bot fly larvae create their own nests, forming cysts and getting oxygen by piercing through the squirrels skin. This causes a swelling on the body of the squirrel. When left alone, the larvae will leave the squirrel, usually during fall months, to pursue the next stage in its development.
Squirrels are quick and nimble animals. They can run, climb, and jump among branches and twigs of the larges trees. When startled on the ground, they scramble up the nearest tree, traveling quickly from tree to tree, never missing a foothold. Squirrels travel in lanes in trees, called travel lanes which they mark by scent. Squirrels will travel from pole to pole along electrical and telephone wires, on trees and houses, often for many city blocks without setting foot on the ground. The typical squirrel home range varies from one to seven acres.
Problems with Humans
At times, squirrels will den in barns, garages, attics and chimneys. This usually involves females entering buildings to establish nests. They will seek any opening while searching for a den site. They will often enter chimneys (if not capped) or attics through unscreened windows or openings left by loose or rotten boards. After the babies are born and old enough to be moved, the mother will move the babies to a natural denning site. Attics and chimneys get very hot and uncomfortable; at that time, the mother will move her youngsters. Complaints about squirrels digging up bulbs and eating fruit and vegetables, and raiding bird feeders are common. There are various gadgets, repellents and methods to alleviate these problems. Having large tree branches hanging over the roof, uncapped chimneys, and openings in the attic, rotten or debilitated latticework on eves of a house, will invite unwelcome guests.
Squirrels and bird feeders
Natural History of Squirrels, John Gurnell, Johnson Nature Series, Squirrels, A Wildlife Handbook, by Kim Long; Furbearing Animals of North America, Leonard Lee Rue III; Information from various sources provided by squirrel researcher Vagn Flyger of Silver Spring, Maryland.