The Arizona gray squirrel is a harmless rodent that co-exists peacefully with humans and other animals in a highly circumscribed habitat. Its future in the United States depends on the preservation of the canyon forests where it makes it home.
Perception Channels: tactile ; chemical
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
This species may be important as a disperser of tree seeds and the spores of mycorrhizal fungi.
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)
Sciurus arizonensis occupies mountain ranges in central Arizona, western New Mexico, and Sonora, Mexico, along the U.S. border. (Best and Riedel 1995)
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
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)
Other Physical Features: endothermic ; bilateral symmetry
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)
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); sexual
This taxon is found in the Arizona Mountain Forests, which extend from the Kaibab Plateau in northern Arizona to south of the Mogollon Plateau into portions of southwestern Mexico and eastern Arizona, USA. The species richness in this ecoregion is moderate, with vertebrate taxa numbering 375 species. The topography consists chiefly of steep foothills and mountains, but includes some deeply dissected high plateaus. Soil types have not been well defined; however, most soils are entisols, with alfisols and inceptisols in upland areas. Stony terrain and rock outcrops occupy large areas on the mountains and foothills.
The Transition Zone in this region (1980 to 2440 m in elevation) comprises a strong Mexican fasciation, including Chihuahua Pine (Pinus leiophylla) and Apache Pine (P. engelmannii) and unique varieties of Ponderosa Pine (P. ponderosa var. arizonica). Such forests are open and park-like and contain many bird species from Mexico seldom seen in the U.S.. The Canadian Zone (above 2000 m) includes mostly Rocky Mountain species of mixed-conifer communities such as Douglas-fir (Pseudotsuga menziesii), Engelmann Spruce (Picea engelmanni), Subalpine Fir (Abies lasiocarpa), and Corkbark Fir (A. lasiocarpa var. arizonica). Dwarf Juniper (Juniperus communis) is an understory shrubby closely associated with spruce/fir forests. Exposed sites include Chihuahua White Pine (Pinus strobiformis), while disturbed north-facing sites consists primarily of Lodgepole Pine (Pinus contorta) or Quaking Aspen (Populus tremuloides).
There are a variety of mammalian species found in this ecoregion, including the endemic Arizona Gray Squirrel (Sciurus arizonensis), an herbivore who feeds on a wide spectrum of berries, bark and other vegetable material. Non-endemic mammals occurring in the ecoregion include: the Banner-tailed Kangaroo Rat (Dipodomys spectabilis NT);Desert Pocket Gopher (Geomys arenarius NT). In addition, there is great potential for restoring Mexican Wolf (Canis lupus) and Grizzly Bear (Ursus arctos horribilis) populations in the area because of its remoteness and juxtaposition to other ecoregions where these species were formerly prevalent.
There are few amphibians found in the Arizona mountain forests. Anuran species occurring here are: Red-spotted Toad (Anaxyrus punctatus); Southwestern Toad (Anaxyrus microscaphus); New Mexico Spadefoot Toad (Spea multiplicata); Woodhouse's Toad (Anaxyrus woodhousii); Northern Leopard Frog (Lithobates pipiens); Chiricahua Leopard Frog (Lithobates chiricahuensis VU); Madrean Treefrog (Hyla eximia), a montane anuran found at the northern limit of its range in this ecoregion; Boreal Chorus Frog (Anaxyrus woodhousii); Western Chorus Frog (Pseudacris triseriata); and Canyon Treefrog (Hyla arenicolor). The Jemez Mountains Salamander (Plethodon neomexicanus NT) is an ecoregion endemic, found only in the Jemez Mountains of Los Alamos and Sandoval counties, New Mexico. Another salamander occurring in the ecoregion is the Tiger Salamander (Ambystoma tigrinum).
A number of reptilian taxa occur in the Arizona mountains forests, including: Gila Monster (Heloderma suspectum NT), often associated with cacti or desert scrub type vegetation; Narrow-headed Garter Snake (Thamnophis rufipunctatus), a near-endemic found chiefly in the Mogollon Rim area; Sonoran Mud Turtle (Kinosternon sonoriense NT).
The Arizona gray squirrel (Sciurus arizonensis) is a tree squirrel, in the genus Sciurus, endemic to the canyons and valleys surrounded by deciduous and mixed forests in eastern Arizona and northern Mexico.
It is threatened by habitat loss. The only other large squirrel that is within its range is Abert's squirrel, which has ear tufts and lives in pine forests. Although they act and look like other gray squirrels, the Arizona gray squirrel is actually more closely related to the fox squirrel.
Sciurus arizonensis is a member of the order Rodentia and the family Sciuridae. It is distinguishable from Sciurus aberti by its longer flatter skull, broader rostrum, and having only one molar instead of two. S. arizonensis also has smaller ears with no tufts and a red/black stripe on the underside of their tail. Some sexual dimorphism can be seen in these squirrels, but it varies with some populations having larger males, and other populations having larger females.[3]
Sciurus arizonensis or the Arizona gray squirrel can be found in parts of Arizona, New Mexico and Sonora, Mexico.[3] They live in the mountains[4] at mid-elevations in riparian habitats, usually broadleaf riparian habitats.[5] The Arizona gray squirrel has had no recent expansion or reduction in the size of their range in New Mexico, though there has been some population decline. This is due to habitat loss and the introduction of Abert’s squirrel, which has in some cases outcompeted the Arizona gray squirrel for resources.[5]
The Arizona gray squirrel's diet consists mainly of pine cones, acorns, and other nuts. They also eat seeds and berries.
Arizona gray squirrels have large variations in their diet, which has led to reproduction rates that vary year by year. Not all females breed each year, which can be seen by a lack of placental scarring. The timing of Arizona gray squirrel mating correlates with the prime time for flowers, which are a high energy food source for the energetically expensive costs of mating.[3] Because mating is so energetically expensive, optimal reproduction timing is very important to ensure that offspring and parent will survive. This timing can differ between sexes and is largely dependent on the environmental change present in their habitat, which can often be fluctuating throughout the year and from year to year.[6] Differences in the parental investment and a lack of food are responsible for shifts in male and female ranges. The opposite sexes have ranges that overlap with each other and during good mating conditions or season these ranges will expand and overlap more.[7] These squirrels have been observed in mating chases with many males chasing one female.[3] An important conservation strategy for the survival of the Arizona gray squirrel is to protect their nesting habitat. This means maintaining large trees with closed canopies that allow access to resources and protection from predators.[3]
The Arizona gray squirrel (Sciurus arizonensis) is a tree squirrel, in the genus Sciurus, endemic to the canyons and valleys surrounded by deciduous and mixed forests in eastern Arizona and northern Mexico.
It is threatened by habitat loss. The only other large squirrel that is within its range is Abert's squirrel, which has ear tufts and lives in pine forests. Although they act and look like other gray squirrels, the Arizona gray squirrel is actually more closely related to the fox squirrel.
