On Mogollon Plateau, Arizona, breeds mostly late April-May. Young are born in June and early July. Litter size is 2-5. Gestation lasts about 40 days. Young are weaned at about 10 weeks, out and about in August. (Hoffmeister 1986).
Basically solitary late spring through fall, nonterritorial (Hall 1981). Average home range in Arizona was estimated at 7.3 ha during summer and fall, 2.0 ha in winter; 18-45 ha in uncut forest in another study. Most of time may be spent in limited area of home range (Hall 1981). Populations seem to fluctuate widely over time. In Arizona, density was estimated at 30/sq km, 2.5-5/sq km, and 30-65/sq km. Feeding by squirrels appears to have neglible effect on ponderosa pine growth (Hall 1981).
Locally Migrant: N
LongDistance Migrant: N
A female followed for one year had a home range of 14 hectares (Hall 1981). Male sciurids typically have substantially larger home ranges than females.
Mainly ponderosa pine forests at elevations of 1800-3000 m. On Kaibab Plateau, optimum habitat consists of relatively open stands of pure pine where trees larger than 15 cm DBH predominate (Hall 1981). May also extend into mixed conifer and upper pinyon-juniper woodland. When active, spends more time on ground than in trees (Arizona, Hall 1981). Builds bulky nests high in pines (nests infrequently in cavities in oak or cottonwood tree. Appears to use several alternate nests (Hall 1981). Nests usually are close to the trunk and more than 10 m above ground (Hall 1981). In northern Arizona, nests were in the crowns of large ponderosa pines, most often on the east to south side of the bole, mostly 10-15 m above ground; tree chemistry appeared to play a role in nest-site selection (Snyder and Linhart 1994).
Feeds primarily on Ponderosa pine: seeds, inner bark (when seeds are scarce), terminal buds, and staminate flowers. Also feeds on fungi (may be important in summer diet), carrion, bones and antlers. May bury single pine cones in shallow pits; apparently does not store food in large caches
Active throughout the year. Diurnal activity begins shortly before sunrise; squirrels return to nests before sunset. In Arizona, most active during the first 4 hours after dawn in summer; midday rest period followed by late afternoon feeding (Hall 1981).
Length: 58 centimeters
Weight: 908 grams
NatureServe. 2010. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. (Accessed: January 14, 2011 ).
Recently park staff have been asked why there seem to be fewer Abert's squirrels (Sciurus aberti) in Rocky Mountain National Park than there were in the past. In answering this question it is important to remember that these shy, often difficult to observe squirrels have very large natural fluctuations in their populations due to food availability. Recent droughts in the area of the park may have resulted in less food available for these specialized feeders. Also, Abert's squirrels have very large home ranges and only occur in mature ponderosa pine (Pinus ponderosa) stands, so increases in human encroachment can cause decreases in Abert's squirrel numbers. Finally, anecdotal evidence suggests that Abert's squirrels are less able to recognize cars as predators than other squirrel species, and are often killed on roads.
Abert's squirrels are one and a half to two pound grayish, reddish, or black squirrels with white undersides. They are most easily distinguished from other squirrels by their prominent ear tufts that are more prominent in the winter and may almost disappear in the summer. Their head and body is about 12 inches long, and their tail is about nine inches. They may live seven to eight years in the wild, although there is little real data on life span.
Ponderosa pine trees provide not only a home but also most of the Abert's squirrel's diet in Rocky Mountain National Park. During the summer they eat the needles, seeds, buds, and male and female cones from these trees. Because they are the only squirrel that does not make food caches, they must be active all year around. During the coldest parts of the winter they will leave their nests for short periods of time to nibble through the ponderosa pine's bark to get to the inner sap conducting layer. When possible, they also eat mushrooms and other fungi, and occasionally they will eat mistletoe, insects, carrion, antlers and bones. They either nest in witches' brooms (misshapen balls of twigs caused by dwarf mistletoe) or make ball-shaped nests, one to three feet in diameter, out of twigs lined with moss, bark, leaves, fur, lichens, and similar materials about 20 to 40 above the ground. Abert's squirrels breed in April or May, carry their young for about 40 days, and usually give birth to three or four babies. Except when breeding or caring for young, they are solitary.
While population numbers may fluctuate from year to year, these fascinating and charming squirrels are in no danger of disappearing from Rocky Mountain National Park.
Abert's squirrels are unique mammals found anywhere in the monument where there are enough Ponderosa pine trees to supply their nutritional needs. Identified by their dark gray backs with a red-brown patch, white bellies, and long fluffy white tails the most destinctive feature of Abert's squirrels are their big tufted ears. Abert's squirrels feed on the cones, buds, and twigs of Ponderosa pine trees as well as fungus and tree sap. With no apparent fear of heights, they can often be seen high in trees scurrying from branch to branch looking for food.
Feeding Habits Abert's squirrels favorite food is the cones of the Ponderosa Pine. They will turn the cone slowly, much like you may rotate an ear of corn as you eat it, peeling away the cone scales to reach the meaty seeds. The new buds and inner bark of the Ponderosa are also quickly consumed by the squirrel. You may think this would be bad for the Ponderosa, however, Abert's also eat ectomycorrhizal fungi. A byproduct of this feeding activity spreads the spores of the fungi around. As it turns out this fungi is very beneficial to the survival of the Ponderosa and the Abert's squirrel serve a vital function in the proliferation of the fungi. The relationship between plant and animal is very interesting and complex.
The eating habits of Abert's squirrels also prove beneficial to mule deer. When the squirrels eat the buds and shoots of the Ponderosa pine they chew off whole twigs. The uneaten portion they drop to the ground many feet below. You can tell where Abert's squirrels have been active by the debris below the Ponderosa pines. The mule deer seem to relish this tree-top treat and quickly consume the messy Abert's trash.
Abert's squirrels build nests high up in Ponderosa pine trees. The nests look similar to a large, messy bird nest. The Abert's collect plant materials including pine duff to line their lofty abode and create a warm, snuggly home. Here, in late spring or early summer, female Abert's give birth to their tiny, pink hairless babies. Young Abert's emerge from these sanctuaries by August and begin to collect food for the winter along side their parents.
In early spring, just as the sap begins to flow in the trees, Abert's squirrel have an interesting addition to their diets. You can often spot an Abert's squirrel clinging to the side of a boxelder tree licking the bark, and the gooey sap below, with their tongue. Boxelder trees are members of the maple family, and have a sweet sap similar to maple syrup. Abert's Squirrels may have developed a sweet tooth by eating this high-energy treat, if only for a short period in the early spring.
In summer, Abert's Squirrels shed their distinctive tasseled ears and their thick winter coat. Since an Abert's ears are still somewhat larger than other squirrel's ears, they still have a very unique appearance. When baby Abert's Squirrels emerge from the nest in late summer, they can easily be distinguished from their parents because they will already have the ear tufts they will continue to wear through the long winter months.