AppearanceAbert's squirrels are 46–58 cm long with a tail of 19–25 cm. The most noticeable characteristic would be their hair ear tufts, which extend up from each ear 2–3 cm. This gives this species a striking similarity to the Eurasian Red Squirrel, aside from its differing dark fur coloration.
They typically have a gray coat with a white underbelly and a very noticeable rusty/reddish colored strip down their back. Aberts found in Colorado rocky mountain foothills appear black all over as shown in the adjacent image.
NamingAbert's squirrel is named after Colonel John James Abert, an American naturalist and military officer who headed the Corps of Topographical Engineers and organized the effort to map the American West in the 19th century.
DistributionAbert's squirrel is confined to the Colorado Plateau and the southern Rocky Mountains of Colorado, Utah, Arizona, and New Mexico; its range extends south in the Sierra Madre Occidental to Chihuahua and Durango in Mexico. Abert's squirrel also extends a short distance into Wyoming where ponderosa pine is present. Abert's squirrels transplanted to the Graham and Santa Catalina mountains of Arizona have established stable populations. Mellott and Choate reported Abert's squirrels present in the Spanish Peaks State Wildlife Area, 43 miles southeast of the previously known Abert's squirrel range.
The distribution of Abert's squirrel subspecies in the Southwest is coincident with the disjunct ponderosa pine forests. Subspecies distributions are as follows:
⤷ ''S. a. aberti'' – northern Arizona
⤷ ''S. a. barberi'' – northwestern Chihuahua
⤷ ''S. a. chuscensis '' – New Mexico-Arizona border area
⤷ ''S. a. durangi'' – Durango
⤷ ''S. a. ferreus'' – Rocky Mountains, central Colorado
⤷ ''S. a. kaibabensis'' – Kaibab Plateau, northern Arizona
⤷ ''S. a. mimus'' – New Mexico-Colorado border area
⤷ ''S. a. navajo'' – southeastern Utah
⤷ ''S. a. phaeurus'' – Durango and extreme southern Chihuahua
BehaviorAbert's squirrel typically builds its nest in the branches of the ponderosa pine in groups of twigs infected with dwarf mistletoe. They are strictly diurnal. Abert's squirrel does not store food, as other North American squirrels do.
HabitatAbert's squirrels make almost exclusive use of ponderosa pine for cover, nesting, and food. Optimum Abert's squirrel habitat is composed of all-aged ponderosa pine stands with trees in even-aged groups, densities of 168 to 250 trees per acre , and 150 to 200 square feet per acre basal area. In optimum habitat average diameter of ponderosa pines is 11 to 13 inches , with Gambel oaks in the 11.8- to 14-inch diameter at breast height range. Optimum habitat has some ponderosa pine over 20 inches d.b.h., which are the best cone producers. Larson and Schubert reported that ponderosa pine 36 to 40 inches d.b.h. produced an average of 446 cones per tree per crop. Trees less than 24 inches d.b.h. produced fewer than 100 cones per crop.
In central Arizona, Abert's squirrel summer home ranges averaged 18 acres and ranged from 10 to 24 acres . Ranges were somewhat smaller in winter. Ramey reported that the mean Abert's squirrel home range for spring and summer was 20 acres in Black Forest County, Colorado. Subadult males had spring home ranges of about 27 acres , and adult females had somewhat larger summer home ranges than adult males. Patton reported the ranges of three squirrels as 10, 30, and 60 acres in Arizona. Hall reported the home range of an adult female as 29 acres .
In Colorado, Ramey found a density of 83 squirrels per square mile in spring 1970 but only 33 squirrels per square mile in spring 1971. In another Colorado study, Farentinos estimated 227 squirrels per square mile in fall 1970 and 317 per square mile in fall 1971.
FoodAbert's squirrels consume ponderosa pine year-round. Parts eaten include seeds, which are the most highly preferred item, inner bark , terminal buds, staminate buds, and pollen cones. Other foods include fleshy fungi , carrion, bones, and antlers. Severe weather is not always a deterrent to feeding activity. Where Mexican pinyon seeds are available, Abert's squirrels consume them in preference to ponderosa pine seeds. Gambel oak acorns may also provide substantial food for Abert's squirrels.
Ponderosa pines produce large cone crops every 3 to 4 years; cones are virtually absent about 1 year out of 4. Abert's squirrels begin eating immature seed shortly after cone development begins in late May. Seeds are eaten through the summer as the cones mature. Seeds from up to 75 cones may be eaten per day per squirrel during the months when seeds form the squirrels' major food. Seeds are disseminated from cones in October and November. Abert's squirrels continue to consume seed from late maturing cones and collect single seeds from the ground. The succulent inner bark of twigs is eaten all year, but most heavily in winter. Needle clusters are clipped from the twigs, the outer bark is removed, the inner bark is consumed, and then the twig is discarded. In winter a single squirrel consumes about 45 twigs per day. Most feed trees range from 11 to 30 inches d.b.h. After seeds have been disseminated Abert's squirrels are dependent on inner bark, which forms the bulk of the diet from November to April. The soft inner tissue of small apical buds is also a preferred item. In May, staminate buds and cones and immature ovules are consumed as available. New staminate cones are entirely consumed; only the pollen is eaten from dried cones. The bark of areas infected with dwarf mistletoe also appears to be preferred.
Fleshy fungi consumed include members of the following genera: ''Agaricus'', ''Amanita'', ''Boletus'', ''Hypholoma'', ''Lepiota'', ''Lycopedon'', ''Russula'' and ''Tuber''. Mushrooms poisonous to humans are consumed by Abert's squirrels without difficulty, including destroying angels and a species of ''Russula''.
Water is obtained mostly from food, but Abert's squirrels sometimes drink at stock ponds or other standing water .
PredatorsReynolds suggested that northern goshawks may take enough Abert's squirrels to regulate Abert's squirrel populations. Hawks prey on Abert's squirrels in central Arizona, but even though other potential predators are present, i.e., gray fox , bobcat , coyote , there is no evidence that they prey on Abert's squirrels.
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