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Photo Courtesy of Utah Division of Wildlife Resources
Abert's Squirrel
Sciurus aberti
NatureServe conservation status
Global (G-rank): G5
State (S-rank): S3
- Reason: There are 10 occurrences of this species in Utah, two of these being historical. It is restricted in Utah to the Abajo and La Sal mountains of San Juan and Grand counties. The species is dependent upon virgin or mature stands of ponderosa pine and thus is threatened by timber harvest, especially clear-cutting, as well as by forest fires. Seemingly it requires hypogeous fungi found in mature ponderosa pine forest as its principal food source.
External links
General information
Often called the tassel-eared squirrel, Abert's squirrel, Sciurus aberti, occurs in ponderosa pine forest habitat in parts of Arizona, New Mexico, Utah, and Colorado. In Utah, the species is very narrowly distributed, occurring only in the southeastern corner of the state, primarily in the Abajo Mountains.
Abert's squirrels depend heavily upon ponderosa pine trees for food, as ponderosa pine seeds, bark, buds, and flowers compose the bulk of their diet. In addition, fungi that grow in association with mature ponderosa pine trees are a major food item during the summer. The species mates in late April or May, and females give birth to a litter of two to five young about forty days after mating.
Abert's squirrels are active during the day throughout the year. Because of their dependance on ponderosa pine trees, logging could pose a threat to the Abert's squirrel.
Phenology
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).
Species range
his species occurs in Utah only in the Abajo and La Sal mountains of San Juan and Grand counties. Boschen (1986) surveyed 38,760 acres inhabited by this species in San Juan County. Before discovery of this species in the La Sal Mountains, Pederson et al. (1976) estimated: "Due to its habitat requirement of ponderosa pine, this subspecies [Sciurus aberti navajo, no longer recognized as valid] is limited to roughly 100,000 acres of this vegetative type on the Monticello Ranger District [in San Juan County]."
Migration
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.
Habitat
Populations occur exclusively in mature stands of ponderosa pine (Durrant 1952). Pederson et al. (1976) reported: "Ponderosa pine is found on the Blue Mountains and Elk Ridge at an elevation of 7,500 feet (2,275 m) to 9,500 feet (2,881.6 m). This tree species prevails on the bench lands surrounding the higher rocky slopes. Aspen (Populus tremuloides), spruce (Picea spp.), and the fir (Abies spp.) complex are found in the north slopes of this area."
Food habits
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
Ecology
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).
Reproductive characteristics
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).
Threats or limiting factors
Logging, especially clear-cutting, of the ponderosaa pine habitat of this species is the principal threat in Utah. Pederson et al. (1987) found that clear-cutting negatively affected the population of this species on study areas in San Juan County. They recommended: "To minimize long-term [negative] effects on [Abert's] squirrels timber should be harvested in small, selective blocks (<20 acres) rather than in large-scale areas (>50 acres) by clear-cut methods commonly employed by management agencies."
References
- Biotics Database. 2005. Utah Division of Wildlife Resources, NatureServe, and the network of Natural Heritage Programs and Conservation Data Centers.
- Burt, W. H. and R. P. Grossenheider. 1980. A field guide to the mammals. Houghton Mifflin Company, Boston. 289 pp.
