Family Sciuridae - Squirrels


MAMMALS OF THE EASTERN UNITED STATES (Whitaker and Hamilton) - Gray, red, fox, flying squirrels and chipmunks all avoid competition by subtle variations in habitat and food preference. The fox and gray squirrel are most similar in size and habits, but are separated geographically, or ecologically, with the fox preferring more open land and the gray, the more closed, dense woods. The smaller red squirrel prefers conifers and uses more den sites than the fox squirrel. Flying squirrels are nocturnal and use much smaller cavities than the fox or gray squirrels. Chipmunks are primarily terrestrial. When the gray and fox do compete, the gray squirrel often replaces the larger fox squirrel.

A nut with a single, smooth-edged elliptical opening at one end is the sign of a flying squirrel. A ragged edge is made by red squirrels, and a nut with two or three smooth-edged holes was done by mice. Finally, a completely fragmented shell can only be made by gray or fox squirrels.

NATURAL HISTORY (10/89) - In 1800's and 1900's, squirrel migrations were common. In 1823, they consumed fields of corn, 3 to 4 per ear. One party killed over 19,000 in a week's time. Fox and red squirrels and chipmunks were seen with the grays. This was a response to food supply. In spring, they eat tree buds, tree flowers, and early seeds, this for energy and Ca and Na (including tombstones), summer they add mulberries, black cherries. In late summer food is scarce and by late July, they lose weight, resorting to inferior mushrooms. In fall, acorns and other nuts appear. But oaks and hickories had erratic mast years, causing these migrations. Tree squirrels eat stored food over winter, ground squirrels hibernate, chipmunks do both. Chipmunks keep a large underground store in their burrows and also have smaller scattered surface stores for last resorts. Gray squirrels tend to bury each nut separately.

Gray squirrels use their jaws like a crowbar; they insert their lower incisors into a hole they have gnawed and snap off chunks of hickories shell, baby grays start their hole near the top of the nut, red squirrels make one hole on each side to get at the kernel, and flying squirrels and chipmunks clean nuts the way we clean pumpkins, removing the top third of the nut and scooping out the insides.

Squirrels definitely prefer hickories; they have twice the calories than acorns. Shagbark has large nuts with thin shells, mockernut has larger nuts with thick shells, and pignuts are small nuts with thin shells (but there is large variation among species and individual trees). Squirrels know each tree; they eat largest nut shagbarks with thinnest shell first, then others. The longest distance traveled from nest to nuts was 250 yards. More of the large, thick-shelled nuts were buried. Winter homes were established by mid-September. The green husks are always removed before caching. Some squirrels use the same cache location and same tree for winter nesting (in this study, the group was made up of an adult female and male and several sub-adults.)

Maryland mammalogist and gray-squirrel authority Vagn Flyger (formerly of U. of Maryland). In 1889, 30 squirrels were released in England and have dominated local indigenous species. They can have five or six nests due to flea problems. This article says they find buried nuts by smell.

Best example of migration was in 1842 when a half a billion grays crossed the Great Lakes area with millions dying due to drownings, predation and disease. Other migrations were reportedly miles wide.

This report says 95 % nut recovery rate.

NATURAL HISTORY (10/94) - This report says up to 74 % of nuts not recovered in mast years. Gray squirrels are opportunistic feeders, including buds of leaves, flowers, spring twigs, insects and an occasional egg.

Red oak acorns cached, white oak eaten, often cached nuts have tip (embryonic tip) of nut nipped off first (especially white oaks). Red oak acorns are rich in fats (18 to 25 %) but laced with 6 to 10 % tannins. White oaks are 5 to 10 % fat and < 2 % tannins. Red oaks germinate in spring, white soon after they fall. Tannins are a natural insecticide, repelling many insects, maybe squirrels. Weevils lay eggs in spring (destroying up to 60 %of the crop of individual trees) nuts which in fall are never cached but eaten on the spot (high protein weevil and all). Many squirrels, jays, and grackles consume the top of red oaks. This is where the weevil is found. It also is opposite the more tannic embryonic tip, which remains viable and is buried.

West Virginia Magazine (10/97) - Unlike other members of the squirrel family such as chipmunks and ground hogs, tree squirrels (fox, gray and red) donít hibernate. Since they mate as early as January, it makes sense to have your food gathered before this time-consuming activity. Fox and gray mate from Jan until March with litters of two to five kits (ave of three) with a gestation period of 45 days. Newborn are 2" and weigh 2 oz., opening their eyes at four to five weeks and weaned at eight weeks. In May, they come out of the tree cavities and stay with the mother for four or five weeks before scattering. Another June mating results in a second litter in July or early August. (only in years following a good mast crop or mild winter)

Gray squirrels weigh 1 1/2 lbs. Fox squirrels weigh 2 lbs. Red squirrels are smaller, with a delayed breeding season of about a month and gestation period of 36 days. Grays prefer mature oak-hickory forests with dense understories. Fox squirrels frequent more open woods and wooded stream bottoms. Thereís a difference between the acorns of the white vs red oak groups. Acorns from the white group (leaves have rounded edges), which mature in one season, germinate in the fall that they drop. Once they germinate, they are inedible to squirrels. So squirrels will eat them first, or, at least "nip" them on the embryonic end so that they wonít germinate. Acorns of the red oak group (with sharp leaf edges), take two years to mature and germinate in the spring after they fall. Thus, they are more often cached away, or "planted" for later retrieval.

BLUE RIDGE COUNTRY (3-4/97) - Summer nests are lined with shredded bark, grass moss and ferns. These cool habitats also are free of mites and ticks that infest permanent tree cavities. If the kit survives the first year, the expected life span is seven years. Like all rodents, their curved incisors grow continuously. For squirrels, this rate is six inches a year. Fall mass migrations were well-documented. An 1842 migration was 130 miles long and 150 miles wide, numbering half a billion squirrels.

National Geographic-Nov,1995 - Order Rodentia, meaning "to gnaw", 18" long-half that being tail, weighing12-26 ounces, both male and female looking alike. Fertile for only one day, females bear a litter between Feb and April. And sometimes another in midsummer. Gestation of 40-44 days, three to five newborns nursed for up to ten weeks. Live 15 - 20 years in captivity, but only a year or so in the wild. 577,211 killed over six months in New York in hunting season. Males have a larger range of up to seven acres. A group of squirrels can attack another group for unknown reasons.

AUDUBON NATURALIST SOCIETY class with Rob Gibbs (3/95)

- Squirrels and apes are the only common diurnal mammals (other than Man).

- gray squirrels tend to dig up own scented buried nuts.

- fox squirrels, being larger than grays, need more mature woods.

- flying squirrels prefer hickory

- gray squirrels break nuts (strong jaws)

- flying squirrels make round hole on top, removing top third.

- chipmunk makes jagged edges, but gnawed all around.

- mice make several holes.

- red squirrels make a hole on each side.

- deer mouse are usually found above 2000'. They donít dig holes.

- the wood rat is also known as a pack rat.

- meadow voles/shrews walk in the snow, whereas mice tend to hop like squirrels.


Data from Brookside Nature Center brochure

Southern flying Squirrel (Glaucomys volans)

Size is ten inches including four-inch tail, weighing 2-3 ounces. Found throughout eastern US forests, replaced in New England by the northern flying squirrel (G. sabrinus). Nests in cavities, preferring hickories(occasionally makes leaf nest - drays). Eats nuts, berries, insects, fungus, occasional bird eggs, small birds and carrion. Breeds in February, gestation 40 days, with a litter born in April and a second in July under favorable conditions. 2-4 per litter (usually three). Altricial young. First flight at seven weeks, mature (breeds) at 7-11 months. Life span of 5 years. Can glide over 100 feet. Often more common than diurnal gray squirrels.

Stokes Nature Guide --- Animal Tracking and Behavior - Diurnal. Home range of several acres, but with much overlap since no territorial protection. Leaf nests in summer, tree cavities in winter. Two broods per year possible (mating Dec/Feb and June/July). Gestation period is 45 days with three per litter the average. Tree cavities are used and protected by females. Young are on their own after 4 months. Males have no role in raising young.