Rodents (Order: Rodentia)

Squirrels (Sciuridae Family)

Ground Squirrel; Photo courtesy of Gerald and Buff Corsi © California Academy of SciencesThree species of squirrels are found at Quail Ridge; one of these is largely terrestrial, whereas the other two are principally arboreal. California ground squirrels (Spermophilus beecheyi) are one of the few diurnal mammals at Quail Ridge. These squirrels are about 40-50 cm (16-20 inches) in length, with a tail that is longer than 50% of the combined head and body length. The back is gray with white specks, and the local subspecies (S. b. douglasii) has a darker patch between the shoulders. The belly is buff colored. Ground squirrels are found in open areas such as meadows, and are a significant agricultural pest in California. Ground squirrels are frequently seen “sitting up” on their hind legs; this vigilance behavior increases their ability to detect potential predators. When threatened by predators, ground squirrels give alarm calls that warn other squirrels of danger; these calls may be confused with those of birds. California ground squirrels have evolved immunity to the venom of western rattlesnakes. In populations sympatric with rattlesnakes, adults are relatively immune, while juveniles and populations outside the range of rattlesnakes are susceptible to venom.

Western Gray Squirrel; Photo courtesy of Tom Greer © 2004 Tom GreerArboreal sciurids include the Sonoma chipmunk (Tamias sonomae) and the western gray squirrel (Sciurus griseus). Sonoma chipmunks are diurnal, have a reddish dorsum, and can be recognized by a series of dark and light stripes that extend from their nose to their rump. California appears to be a hotbed of chipmunk speciation, and species here are notoriously difficult to distinguish; however, as no other chipmunks occur in the area, chipmunk identification is easy at Quail Ridge. These chipmunks occur in chaparral and grassland habitats and are rarely seen. Western gray squirrels have a smoky gray coat with a white underside and a long bushy tail. They may be distinguished from California ground squirrels by their white belly and bushier tail. These squirrels can be seen foraging among oak or pine trees and on the ground in oak woodlands. Evidence of their presence in an area is nests made out of leaves, sticks, and bark high up in trees, and chewed pine cones.

Pocket Gophers (Geomyidae Family)

Botta pocket gopher; Photo courtesy of Dr. Lloyd Glenn Ingles © California Academy of SciencesBotta pocket gophers (Thomomys bottae) are primarily subterranean, and they have many adaptations to their fossorial lifestyle, such as extremely small eyes and ears, a short tail, and long claws for digging. These animals are brownish to light gray above and gray to white underneath. Their burrows are much more visible than the actual animals; burrows are indicated by piles of fine soil with an opening plugged diurnally with dirt. Botta pocker gophers live in open habitats, such as grassland.

Pocket mice (Heteromyidae Family)

The San Joaquin pocket mouse (Perognathus inornatus) has been captured only once at Quail Ridge. This species weighs 7-12 g (0.25-0.42 ounces) and has an orange buffy pelage and short ears. It can be distinguished from other small mammal species at Quail Ridge by having external fur-lined cheek pouches that can be stuffed with food, which is transported to the burrow for later use. The pocket mouse generally is found in grasslands.

Rats and Mice (Muridae Family)

Old World Rats and Mice (Subfamily Murinae)

Considered vermin to most, house mice (Mus musculus), black rats (Rattus rattus), and Norway rats (R. norvegicus) were introduced to North America early in the exploration of the continent and have been very successful in a variety of habitats. House mice will occupy any human structure with shelter and food, and they are very effective at colonizing many native habitats as well, such as riparian corridors in the Central Valley. They are not prevalent at Quail Ridge, but if found they can be distinguished from other rodents by their small size, naked (hairless) and scaly tail, and a pungent smell. Additionally, the upper incisors are notched in side view, unlike other small rodents in California. These species are remarkably rapid breeders, and they do compete with native small mammals, so should be euthanized if encountered.

The two rat species are in the size range of the woodrat (e.g., 100-350 and 200-500 g (3.53-12.35 and 7.06-17.64 ounces) for the black and Norway rats, respectively), however, unlike the woodrat, these two species do not have hairy tails; they are naked and scaly. Black rats are smaller than Norway rats, and the tail in the former is longer than the head and body length, whereas it is generally somewhat shorter in the latter species. To date neither of these species have been documented at Quail Ridge, but it seems inevitable that one of them (most likely the black rat) will arrive; they should be eradicated on sight, as they are prolific breeders, voracious nest predators, and strong competitors to native rats and mice.

New World Rats and Mice (Subfamily Sigmodontinae)

The smallest sigmodontine rodent at Quail Ridge is the western harvest mouse (Reithrodontomys megalotis). These animals are tiny (typically 9-12 g (0.32-0.42 ounces) at Quail Ridge) and have pale gray to brownish dorsal pelage with a grayish ventrum. Hairs in the ears, on the feet, and around the rostrum often are tinged with orange coloration. These mice can be distinguished from all other species at Quail Ridge by their grooved upper incisors. Harvest mice are particularly common in grasslands and chaparral.

Three species of deer mice (genus Peromyscus) may occur at Quail Ridge, although only two have been documented to date. The deer mouse (Peromyscus maniculatus) is brownish dorsally (although color may range from yellowish brown to gray; juveniles typically have gray pelage) and white ventrally. The tail is bicolored and generally shorter than the combined head and body length (about 90%). Adult deer mice Deer Mouse; Photo courtesy of William Leonard © 2005 William Leonard(excluding pregnant females) typically weigh 14-20 g (0.49-0.71 ounces) at Quail Ridge. This is one of the most widely ranging mammal species in North America; it is found in almost all habitat types throughout the continent. At Quail Ridge, it is more plentiful in riparian areas (such as Decker Canyon) than in drier habitats. A larger species is the brush mouse (Peromyscus boylii), which is one of the most abundant small mammal species at Quail Ridge. Brown dorsally and white ventrally, brush mice can be distinguished from deer mice by the larger body size – adults (excluding pregnant females) weigh 23-30 g (0.81-1.06 ounces) – a tail that is longer than the combined head and body length, a tuft of hair at the end of the tail, and an orangish stripe on either side of the body,. Their hind foot typically is shorter than the ear. Brush mice typically are found in chaparral and oak woodland areas. The third species is the pinyon mouse (Peromyscus truei). Pinyon mice have not been documented at Quail Ridge, although they occur at the nearby Cold Canyon and McLaughlin Reserves. Pinyon mice can be difficult to distinguish from brush mice. The most reliable character is ear length; pinyon mice have very long ears (as long or longer than the hind foot), while brush mice have ears that are approximately 70-80% of hind foot length. Pinyon mice tend to be found in woodland habitats.

The largest member of this group is the dusky-footed wood rat (Neotoma fuscipes); these animals, part of a group often referred to as pack rats, construct large stick houses, which may be either on the ground or more than 2 m high in trees. Grayish brown dorsally and grayish to whitish below, woodrats are clearly distinguished by the presence of dusky patches of fur on the feet. Dusky-footed wood rats are found in riparian, oak woodland, and chaparral habitats, and seem to be particularly abundant at Quail Ridge.

Meadow mice and Voles (Subfamily Arvicolinae)

The California vole (Microtus californicus) is a coarse brownish above and gray-brown to whitish below. The tail is less than 1/3 the length of the head and body, and the ears are barely visible. California voles inhabit grassy meadows at Quail Ridge and construct runways through tall grass. They are largely herbivorous, switching to seeds in summer when green vegetation dies. Voles are important prey for some raptors, especially white-tailed kites, which are virtually vole specialists.

Species Accounts

Mammals Page

Photo Credits: Title, Mule Deer (Mike Benard), Ground Squirrel (Gerald and Buff Corsi), Western Gray Squirrel (Tom Greer), Botta pocket gopher (Dr. Lloyd Glenn Ingles), Deer Mouse (William Leonard). For more pictures see:

This page last updated: June 24, 2005  

Contact: Dr. Virginia Boucher
John Muir Institute of the Environment
109 The Barn, University of California, Davis, CA 95616
Phone: 530-752-6949; email:

Site designed and maintained by Shane Waddell
Website Technical Questions: