Walnuts are a favorite food of Arizona Gray Squirrels, and when they find an abundance, the squirrels soon stain their faces, paws, and undersides a distinct brownish-orange from walnut juice. Other foods eaten may include fungi, acorns, juniper berries, pine seeds, and tree flowers and buds. This species is quiet and secretive and rarely seen. It is not very common and has a limited geographic distribution. Within its range, Arizona Gray Squirrels prefer broadleaf forests along rivers, which commonly occur in canyon bottoms.

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This species occurs in south-western U.S.A. (Arizona and New Mexico) and adjoining Mexico (Sonora), with three disjunct population segments: western and southern mountains of central Arizona high country (below Mogollon Rim) and a few localities in western New Mexico, isolated mountain ranges in southern Arizona, and southern Arizona mountains extending into northern Sonora. Found between 1,120 and 2,700 m asl in elevation.

Sciurus arizonensis occupies mountain ranges in central Arizona, western New Mexico, and Sonora, Mexico, along the U.S. border. (Best and Riedel 1995)

occurs (regularly, as a native taxon) in multiple nations

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Central and southeastern Arizona (southern and western slopes of the Mogollon Plateau from north of Sedona, Coconino County, to Blue, Greenlee County, and many isolated mountain ranges to the south, including the Prescott, Bradshaw, Pine, Mazatzal, Sierra Ancha, Santa Catalina, Rincon, Santa Rita, Patagonia, Pajarito, and Atascosa mountains); west-central New Mexico (watersheds of the San Francisco and Gila rivers in Catron County, Pinos Altos Mountains in Grant County); northeastern Sonora, Mexico (Sierra de los Ajos, Sierra Azul, Sierra de la Madera, Sierra Patagonia, Sierra de Pinitos, and mountains northeast of Cucurpe) (Hoffmann et al., in Wilson and Reeder 1993, Best and Riedel 1995); 1120 m to above 2700 m (Best and Riedel 1995).

Known commonly as the Arizona gray squirrel, Sciurus arizonensis is gray in color throughout most of its upper body. Patches of yellow are sometimes present behind the ears. The tail is black dorsally and yellow to brown ventrally. The two sides of the tail are separated by white edging, and the underparts of the squirrel also are white. The squirrel's gray pelage darkens during the winter, and its underparts and feet are often stained from walnut juice (see Food Habits). Total body length for the species, including the tail, averages 21 inches. (Best and Riedel 1995) (Cockrum 1992)

Length: 57 cm

Weight: 706 grams

Sexual Dimorphism: None

Length:
Range: 455-574 mm

Weight:
Average: 655g
Range: 527-884 g

See Best and Riedel (1995).

Habitat and Ecology

Systems

• Terrestrial

In Arizona, S. arizonensis occurs in dense, mixed-broadleaf communities of riparian-deciduous forest. Usually, the species is restricted to elevations of 1,500 to 1,900 meters above sea level. Favored habitats are groves of old cavity-prone Arizona sycamores and other large deciduous trees. In New Mexico, the squirrel is confined to deep canyons with water, where black walnuts and acorns are abundant. In Mexico, the squirrel occupies riparian forests at lower elevations than does its Arizona cousin. (Best and Riedel 1995) (Cockrum 1992) (Findley 1987)

Terrestrial Biomes: forest ; mountains

Comments: Hardwood and mixed oak and pine forests. Found in river valleys and canyons. Found where black walnuts and acorns are abundant. Also in cottonwood and sycamore groves. Makes leaf nests in trees.

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Sciurus arizonensis may feed on a wide variety of vegetable material, including nuts, fruits, bark, berries, flowers, and fungi. The actual breadth of the diet depends on the availability of food sources and the particular geographic range of the animal. In New Mexico, S. arizonensis feeds almost exclusively on walnuts, supplemented by roots. In Arizona and Mexico, the gray squirrel eats walnuts, but also acorns, juniper berries, hackberries, pine seeds, and fungi. The diet of these squirrels is more varied on a seasonal basis as well. In late summer and early autumn, the Arizona- and Mexico-based squirrels take in insects and other animal matter. Walnuts are a staple for S. arizonensis regardless of geographic range, and several individuals often harvest these nuts in the same tree. Another dietary habit shared by all members of the species is the consumption of flower parts in late winter and early spring. This seasonal food source is thought to be linked to reproductive activity (see Reproduction). (Best and Riedel 1995)

Comments: Mast, especially walnuts and acorns, pine seeds, flowers, buds, fungi, and other vegetation. May also eat insects.

Populations seem to fluctuate, but more information is needed.

The onset of breeding activity in the Arizona gray squirrel is correlated with flower emergence and the inclusion of flower parts in the diet. It is theorized that the flower parts contain vitamin A and other vitamins that stimulate reproductive activity. Estrus occurs in females in April and early May. Mating chases also occur during this time, with several males pursuing a single female. Not all females breed each year. Gestation usually lasts about two months, and the litter size ranges from two to four offspring. (Best and Riedel 1995)

Sexual activity apprently extends from January to June. Juveniles taken in mid-August suggest births in mid-June. No evidence of second annual litter or fall litter (Hoffmeister 1986).

The population of Arizona gray squirrels in the United States is fairly small, a situation that may be connected to competition from Sciurus aberti, a hardier squirrel and a close relative. The United States Department of the Interior, Fish and Wildlife Service classifies the Arizona gray squirrel as a "Category 2" species, which is reserved for taxa that may be eligible for threatened or endangered status. In Mexico, S. arizonensis has suffered severe habitat loss due to logging and the clearing of forests for agricultural use. The squirrel is rare in Mexico and is considered a threatened species in the that country. (Best and Riedel 1995)

IUCN Red List of Threatened Species: data deficient

United States

Rounded National Status Rank: N4 - Apparently Secure

Rounded Global Status Rank: G4 - Apparently Secure

Near Threatened.

Population

Population Trend

Major Threats

Conservation Actions

This species may be important as a disperser of tree seeds and the spores of mycorrhizal fungi.

Comments: Sciurus arizonensis may be conspecific with S. nayaritensis (Hoffmeister 1986). Scirurus nayaritensis and S. arizonensis may be subspecies of S. niger (see Best and Riedel 1995). Hoffmeister (1986) examined geographic morphological variation and concluded that S. arizonensis is best treated as monotypic (though a somewhat variable unit). Thorington and Hoffman (in Wilson and Reeder 2005) recognized arizonensis, nayaritensis, and niger as distinct species and recognized three subspecies of S. arizonensis (arizonensis, catalinae, and huachuca).