Botta’s pocket gopher (Thomomys bottae), which is also known as the valley pocket gopher is ahighly adaptable small mammal that has found a home, among, other places, in the expanses of San Bernardino County.
Botta’s pocket gopher is a medium-sized gopher, with adults reaching a length of roughly seven to ten-and-a-half inches, including a two to two-and-a-half inch tail. Males are larger, with a weight of 5.6 to 8.8 ounces, compared with 4.2 to 7.1 ounces in the females. Coloration is highly variable, and has been used to help distinguish some of the many subspecies; it may also change over the course of a year as the animals molt. Both albino and melanistic individuals have also been reported. However, Botta’s gopher generally lacks the black stripe down the middle of the back found in the closely related southern pocket gopher. They have furlined cheek pouches.
In addition to being native to California, these creatures are present in Arizona, Nevada, New Mexico, Texas, Utah and southern Colorado and Mexico. Within this geographical area, they inhabit a range of habitats, including woodlands, chaparral, scrubland, and agricultural land, being limited only by rocky terrain, barren deserts, and major rivers. They are found at elevations up to 13,800 feet.
There are roughly 195 subspecies of the Botta’s pocket gopher, and many of these have evolved because of their geographical distribution and the differences in climate and habitat. California boasts 43 subspecies
Botta’s pocket gopher is strictly herbivorous, feeding on a variety of plant matter. Shoots and grasses are particularly important, supplemented by roots, tubers, and bulbs during the winter. An individual will often pull plants into the ground by the roots to consume them in the safety of its burrow, where it spends 90 percent of its life.
Main predators of this species include American badgers, coyotes, long-tailed weasels, and snakes, but other predators include skunks, owls, bobcats, and hawks. This species is considered a pest in urban and agricultural areas due to its burrowing habit and its predilection for alfalfa. Paradoxically, it is also considered beneficial as its burrows are a key source of aeration for soils in the region. Digging by Botta’s pocket gophers is estimated to aerate the soil to a depth of about eight inches and to be responsible for the creation of Mima mounds up to six-and-a-half feet in height. Populations of the species have been estimated to mine as much as 28 tons of soil per hectare per year, much of which is moved below ground, rather than being pushed up into the mounds. On the negative side, the species has been associated with the deaths of aspen in Arizona and creates patches of bare ground that may limit the establishment of new seedlings.
The Botta’s pocket gopher is highly adaptable, burrowing into a very diverse array of soils from loose sands to tightly packed clays, and from arid deserts to high altitude meadows. They are able to tolerate such a wide range of soils in part because they dig primarily with their teeth, which are larger and with a thicker layer of enamel than in claw-digging gophers. In comparison, gophers digging with their claws are generally only able to dig in softer soils, because their claws wear down more quickly than teeth do in harder materials.
Botta’s pocket gophers are active for a total of about nine hours each day, spending most of their time feeding in their burrows, but are not restricted to either daylight or night time. They make little sound, although they do communicate by making clicking noises, soft hisses, and squeaks.
Their burrows include multiple deep chambers for nesting, food storage, and defecation, that are as much as five feet below ground. A series of tunnels close to the surface are used for feeding on plant roots, and have shorter side tunnels for disposal of excavated soil. On the surface, the burrows are marked by fan-shaped mounds of excavated soil, with the actual entrance usually kept filled in for protection. Population densities of between 10 and 62 per acre have been reported.
Above ground traces of these burrows are sometimes called “gopher eskers.”
Outside of the breeding season, each burrow is inhabited by a single adult, with any young leaving once they are weaned. Male burrows extend over a mean area of 5,100 square feet, and those of females 3,080 square feet. The gophers aggressively defend a larger exclusive area, of up to 8,700 square feet for males and 4,200 square feet for females, around the burrow entrance.
Tunnel systems more than 450 feet in length are not rare. These ramified travelways assist the occupants in avoiding avoid predators that try to search them out; they are equally important in permitting the gopher to forage over a considerable area without exposure to undue danger. In winter, if snow covers the ground, the gophers often extend their burrows into the snow and can then forage aboveground in safety.
Although pocket gophers are active the year round, they store food to carry them over periods of scarcity, especially periods of drought when food is scarce and burrowing a difficult task. Usually, only one adult animal occupies each burrow system except for a short time in the breeding period. Associated with this solitary habit is a ferocious and seemingly fearless disposition. When two gophers encounter each other, they will fight or meticulously avoid each other. Desire for companionship seems to be completely lacking in their makeup.
In areas with sufficient food, such as agricultural land, breeding can occur year round, with up to four litters being born each year. In the north, and other, less hospitable, environments, breeding occurs only during the spring. The local habitat also affects the age at which females begin breeding, with nearly half doing so in their first year in agricultural land, but none at all in desert scrub.
Gestation lasts eighteen days, and results in the birth of a litter of up to twelve pups, although three or four is more typical. The young are born hairless and blind, and measure about two inches in length. The first, silky coat of fur is replaced by a coarser coat of grey hair as the pups age, before the full adult coat develops.
Botta’s pocket gophers are capable of breeding with southern pocket gophers, and, until the 1980s, were often considered to belong to the same species. However, male hybrids are sterile, and females have greatly reduced fertility and rarely have offspring of their own. Hybridisation with Townsend’s pocket gopher has also been reported, and it too appears not to extend much beyond the first generation.
The specific and common names of this species honor Paul-Émile Botta, a naturalist and archaeologist who collected mammals in California in the 1820s and 1830s.