Tamias evolved by the early Miocene, but no fossils of T. sonomae are known. Over a large area of northwestern California, the range of T. sonomae overlaps that of T. ochrogeys, T. siskiyou, or T. senex.
Some sources still place the Sonoma chipmunk in the genus Eutamias.
Tamias is from the Greek tamias meaning storer or distributor. The specific epithet sonomae apparently refers to Sonoma Co., where the type specimen was obtained.
Best (1993)
Perception Channels: tactile ; chemical
The sonoma chipmunk's small range and the very small number of studies on its key habitats and forage resourses makes it difficult to determine its status. More research is needed to determine whether human activities or land use are a threat to this species. Nonetheless, it should be noted that several other Tamias species in the western United States may be in jeopardy becuase of human environmental disturbance. In fact, Tamias minimus atristriatus, of central New Mexico, evidently became extinct around 1980 when its limited habitat was lost to residential development. Nowak (1991)
IUCN Red List of Threatened Species: least concern
Other species in the genus Tamias that also prefer rugged or brush-covered land have been known to damage agricultural crops by eating planted seeds and young plantings. Fruit trees have also been damaged by Tamias species in some areas. Nowak (1991)
The skins of another species in the Tamias genus, T. sibiricus, are used to some extent in the fur industry. Also, the sonoma chipmunk may be an important disperser of seeds and the spores of mycorrhizal fungi in the habitats in which it lives. Nowak (1991)
The sonoma chipunk has not been extensively studied and therefore little is known about its food habits. Nonetheless, considering its habitat, T. sonomae probably eats seeds and leaves of chaparral plants. Common plants within the sonoma chipmunk's range include whitethorn, chokecherry, serviceberry, and silk tassel. It is reasonable to assume that T. sonomae follows the food habits of other species within the genus Tamias. Other species within this genus are known to eat the fruits and seeds of various trees and herbs. The foliage and flowers of some herbs are also eaten, as are the tender buds of woody plants. Mushrooms, insects, bulbs, and birds' eggs are also consumed at times.
Best (1993), Nowak (1991)
NW California, from San Francisco Bay north to Siskiyou Co. (USA) Hall (1981), Wilson and Reeder (1993)
Biogeographic Regions: nearctic (Native )
Tamias sonomae requires habitat with trees, shrubs, logs, snags, and litter. It occurs in chaparral and open areas in redwood forests and the lower and drier forests of Ponderosa pine. It also lives in areas characterized by Douglas fir, black oak, and laurel. Elevationally, it lives in areas from near sea level to 1800 meters in elevation. Best (1993), California Wildlife Habitat Relationships Systems (1997), Nowak (1991)
Terrestrial Biomes: savanna or grassland ; chaparral
Length: 25-125 g Tail: 220-227 mm
Hind foot: 33-37 mm
Ear (length from notch): 15-23 mm
Cranium (greatest length): 36.6-39.7 mm
Cranium (breadth): 15.0-16.5 mm
Baculum: 3.03-3.30 mm
Males and females are externally similar; there is no apparent sexual dimorphism. The Sonoma chipmunk has five black longitudinal back stripes separated by four dull gray or brownish stripes. In contrast to other western American chipmunks, however, the back stripes are not clearly demarcated (this lack of clearly demarcated stripes is believed to help camouflage the sonoma chipmunk in its chaparral habitat). The remainder of the upper parts are reddish brown in color, except for a small patch of black fur immediately behind each eye and whitish stripes on either side of each eye. The sides of the body are rusty in color and the ventral surface is creamy white. The tail is quite bushy and follows the color of the body both ventrally and dorsally. The fur is soft and dense, and it becomes slightly woolly in the winter. There are two molts each year, giving rise to a summer pelage (July-September) and a winter pelage (November-June), the summer pelage being brighter than the winter pelage.
There are two recognized subspecies of T. sonomae, T. s. alleni and T. s. sonomae (the first occupying the southern most part of range of this species). T. s. alleni is slightly smaller than T. s. sonomae, and its pelage is darker.
The skull of the sonoma chipmunk is long and narrow, the zygomatic breadth averaging 54% of the greatest length of the skull. The rostrum is deep, the nasals are separated at the tips by a small median notch, and the braincase is long and inflated. The incisive foramina are short. The dental formula is 1/1, 0/0, 2/1, 3/3, for a total of 22 teeth. The upper incisors are recurved, with a sharp-angled notch in the occlusal surfaces, and the cheek teeth are relatively small. The baculum has a thin shaft and a low keel that extends 10% of the length of the tip. The tip is 27-31% of the length of the shaft. The angle formed by the tip and shaft is 130 degrees, and the distal end of the shaft is slightly compressed laterally.
Best (1993), Ingles (1965), Nowak (1991)
Other Physical Features: endothermic ; bilateral symmetry
Females breed once per year in the spring. However, females from low elevations may enter estrus five or more months before females from high elevations. The gestation period is 31 days, and lactation lasts 39-45 days. Litters consist of three to five (usually four) young, and females alone raise the litter. They stay with the young and suckle them, at least at night, for at least three weeks after the young emerge. Weaned young remain together for some weeks after the mother no longer associates with them. The testes of adult males enlarge during the breeding season, during which the males are said to have scrotal testes (December-June). In late March, the testes of adult males reach 13-16.5 mm in length. The age at sexual maturity for males or females is unknown.
Best (1993), Nowak (1991)
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); sexual
The Sonoma chipmunk (Neotamias sonomae) is a species of rodent in the squirrel family Sciuridae. It is endemic to northwestern California in the United States.[1] Members of Neotamias are characterized by having 2 premolars.[2] N. sonomae has 2 subspecies: N. s. alleni and N. s. sonomae.[3]
The Sonoma chipmunk is only found in California, north of the San Francisco Bay. Most of its range is within Sonoma and Marin counties.[3]
Sonoma chipmunks are found in areas of forest or chaparral. They can be found in forests of sticky laurel, Ponderosa pine, Douglas fir, spruce, redwood, and black oak. They are generally associated with coniferous forests. The chaparral that Sonoma chipmunks inhabit is characterized by sagebrush plains.[2] Sonoma chipmunks are found in elevations from 0 to 1800 m.[3] These chipmunks typically live on the ground and make burrows in the ground, but they can climb and may make nests in trees.[2]
The Sonoma chipmunk has a total body length (including tail) ranging from 220-264mm. Tail length ranges from 100-126mm, hind foot (pes) length is 34-39mm, and ear flap (pinna) length is 15-19mm.[3] These chipmunks have 5 black/brown stripes running the length of their body with white stripes in between.[2] The rest of the dorsal and ventral parts of the body range from tawny to cinnamon to gray. The tail is edged in white. The belly is grayish white. Sonoma chipmunks have 2 molts per year, having a summer and winter pelage. The winter pelage is generally slightly darker and duller than the summer pelage. N. s. alleni is smaller and darker than N. s. sonomae. There is no distinct sexual dimorphism.[3]
There are 2 other species of chipmunks found in the geographic range of the Sonoma chipmunk: the yellow-pine chipmunk and the Townsend's chipmunk. The yellow-pine chipmunk will be smaller and less reddish than N. sonomae and will lack a white-edged tail. N. sonomae can be distinguished from the Townsend's chipmunk by having longer ears, tail, and legs, being paler, and having a bushier tail.[3]
The skulls of Sonoma chipmunks have the distinct post orbital process that is found in all sciurids.[2] The skull has a deep rostrum, a long braincase, and small incisive foramina.[3] The incisors are curved and pincer-like, and the molars are simple and cuspidate. The dental formula for N. sonomae is 1.0.2.31.0.1.3 × 2 = 22.[2]
Sonoma chipmunks typically forage on the ground or climb along small branches in brush.[3] They eat seeds, fruits, herbs, buds of woody plants, as well as insects and bird eggs. Food is collected in their cheek pouches and stored in their burrows.[2] These chipmunks will find elevated places to eat and rest so they can watch the surrounding area for predators. Sonoma chipmunks have high-pitched, bird-like alarm calls that are distinct from other chipmunks and are emitted in response to potential threats. Females are usually the ones to make alarm calls. These alarm calls likely evolved due to kin selection, as the chipmunks nearby that hear the alarm calls are typically related to the individual making the alarm call. When an alarm call is heard, the chipmunk will quickly move along a direct path to a covered, protected area and become still.[3] These chipmunks undergo torpor in winter but arise periodically to eat from their food cache, since they do not accumulate fat stores.[2]
Sonoma chipmunks breed once per year, anywhere from February to July, but most often in April to May. There is occasionally a second breeding season for females if their first litter is lost. Gestation lasts for 28–36 days.[2] 3-5 young are produced per litter, but it is usually 4. The babies are weaned after approximately 3 weeks, and the mother stops associating with them after they are weaned. The juveniles stay together for a few more weeks after their mother leaves. After this, the juveniles disperse.[3] Males disperse in a larger range than females. Juveniles reach sexual maturity within one year, and the lifespan of these chipmunks is around 64 months.[2] Females have higher survivorship and live longer than males. There is a 1:1 ratio of males to females when the juveniles disperse in spring. By the end of the year, this ratio favors females due to the higher risk of mortality in the wider ranging males. However, the ratio again becomes 1:1 by the fall of their second year of life, as first-year adult females have a high risk of mortality during their first breeding attempt. Over time, the ratio will once again favor females.[3]
Sonoma chipmunk, juvenile (left) and adult (right) The Sonoma chipmunk (Neotamias sonomae) is a species of rodent in the squirrel family Sciuridae. It is endemic to northwestern California in the United States. Members of Neotamias are characterized by having 2 premolars. N. sonomae has 2 subspecies: N. s. alleni and N. s. sonomae.
