Thomomys mazama
western pocket gopher

Thomomys mazama is found in the Pacific Northwest of the United States. Populations occur in Washington, Oregon, and California (Verts and Carraway, 2000).

Thomomys mazama usually occupies a narrower array of niches than other species of Thomomys. Thomomys mazama is found in a variety of soil types in prairies, meadows, orchards, and abandoned farms. They are not frequently found in dense forest. Common vegetation in the habitats of T. mazama includes bracken fern, Douglas fir, perennial grasses, red sorrel, and western strawberry.

Thomomys mazama is highly fossorial. It is adapted for this mode of life with heavily muscled shoulders and head tapering to relatively narrow hips. It has short limbs with five toes on each of the four feet. The toes on the front limbs have much longer curved claws than the hind limbs. The eyes and ears are small. The skull is flattened dorso-ventrally and has wide spreading zygomatic arches. The mandibles are heavy (Verts and Carraway, 2000).

The dorsal pelage of T. mazama exhibits a large range of colors in various subspecies. It is a shiny iridescent black in the subspecies T. m. niger. In T. m. tumuli and T. m. pugetensis it is blackish brown. The fur is dark brown in T. m. fuscus and T. m. louiei; reddish brown in T. m. hesperus, T. m. mazama, T. m. helleri, and T. m. melanops; reddish tan in T. m. couchi and T. m. tacomensis; light yellowish brown in T. m. nasicus, T. m. premaxillaris, and T. m. glacialis; and light brown in T. m. oregonus and T. m. yelmensis. The nose and face are dusky or black. The chest often has white splotches. The tip of the tail is lighter colored, usually buff, white, or light gray and may be almost naked.

Male T. mazama are generally larger than females. The total average length of T. mazama is 204 mm for females and 213 mm for males. The average tail length is 62 mm for females and 64.5 mm for males. The baculum is commonly used to differentiate between juveniles and adults. It is long and slender. The minimum length to be classified as an adult is 21-22 mm, but it can reach a length of about 26 mm. The dental formula for T. mazama is i 1/1 c 0/0 p 1/1 m 3/3 with a total of 20 teeth. The premolars are figure eight shaped. Chewing is propalinal (Verts and Carraway, 2000). (Verts and Carraway, 2000)

There is little information on the mating behavior of T. mazama. Individuals seem to rely on encountering each other through normal daily movement (Scheffer, 1938).

Mating has not been observed in captivity for T. mazama, but reproductive behavior can be inferred from individuals taken in from the wild. The females produce one litter per year during the October to June breeding season. The average litter size is five. The period of gestation is about one month and depends on environmental factors. Under extreme stress, one or more embryos may be reabsorbed (Scheffer, 1938).

Thomomys mazama leads a fossorial life, spending most of its time in burrow systems it constructs or finds unoccupied. These burrows are 3.8-4.4 cm in diameter and are generally 10-15 cm below the surface. A vertical tunnel goes to deeper burrows that include the nest. Crescent shaped mounds of earth are formed when earth is excavated and lie at the surface. Nests are about 25 cm in diameter and 15 cm high and are lined with dry grass and root cuttings. Feces are left in nearby waste chambers. Individuals are generally solitary and are found together in burrows only during mating season. Thomomys mazama forages underground by snipping off roots while in their burrows. They sometimes forage above ground at night. They stay close to the openings of their burrows while they load their cheek pouches with vegetation before quickly going back underground. They repeat this process throughout the night. They do not eat while on the surface (Verts and Carraway, 2000).

The average home ranges of T. mazama are 97 square meters for females and 108 square meters for males (Witmer, 1996).

Grasses compose the largest portion of the diet of T. mazama annually. Woody plants such as Ponderosa pine were consumed mostly in the winter. Roots were eaten mostly in the autumn and spring and compose a large portion of the diet during these periods. Forbs are preferred when many food sources are available. In general, consumption of various species of plants corresponded to their abundance (Verts and Carraway, 2000).

Anti-predator adaptations are primarily behavioral. Thomamys mazama lives underground and emerges only briefly at night to forage. If threatened it retreats underground (Verts and Carraway, 2000).

Thomomys mazama may play an important role in the aeration, mixing, and drainage of soil. They also contribute to the distribution and succession of plant species and communities. They are a source of food to many mammals and birds. Their burrows are used and inhabited by many other species. Their ecological importance is suggested by the fact that there is an ecological equivalent to the gopher on almost every continent (Witmer, 1996).

Thomomys mazama can cause the failure of forest plantings because they eat the roots, leaves, and stems of the seedlings. This has led to efforts to control and eliminate gopher populations with repellents and toxins (Witmer, 2000).

As of 1998 T. mazama was listed as a candidate species by the Washington Department of Fish and Wildlife and as a species of concern by the U.S. Fish and Wildlife Service but was not included in lists of threatened species from the Oregon Department of Fish and Wildlife or the California Department of Fish and Game (Verts and Carraway, 2000).

There are many subspecies because they are easily isolated by rocky, wet, or very compact soil; by frequent agricultural plowing of the land; or by dense forest (Whitmer, 1996).