Thomomys mazama 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Mammalia Rodentia Geomyidae

Scientific Name: Thomomys mazama Merriam, 1897
Common Name(s):
English Western Pocket Gopher, Mazama Pocket Gopher, Puget Sound Pocket Gopher
Taxonomic Notes: Thomomys mazama was regarded as a subspecies of T. monticola in some older literature.

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2016
Date Assessed: 2016-08-18
Assessor(s): Cassola, F.
Reviewer(s): Amori, G.
Contributor(s): Hammerson, G.A. & Linzey, A.
Listed as Least Concern because its range is much greater than 20,000 km², it occurs in several protected areas, and its population is unlikely to be declining fast enough to qualify for listing in a more threatened category. There are major threats identified for this species, and its range is fragmented so it may become threatened in the future if threats continue.
Previously published Red List assessments:

Geographic Range [top]

Range Description:This species has a relatively limited distribution along the Pacific coast of the United States from Washington to northern California (Hafner et al. 1998). The overall range is comprised of multiple disjunct population segments (Verts and Carraway 2000).
Countries occurrence:
United States (California, Oregon, Washington)
Additional data:
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:The total adult population size is unknown but likely exceeds 100,000, with the great majority in Oregon. In Washington, most surviving populations are small (<100) and appear to be isolated from other populations (Stinson 2005). The total of all remaining populations of T. mazama in Washington may be between two thousand and five thousand individuals.

Based on 1,394 specimens, Verts and Carraway (1998) mapped roughly 200 collection sites in the central portion of the range in Oregon. About 27 populations remain in Washington (Stinson 2005). In Washington, additional surveys are needed to document remnant populations in the rapidly developing areas on historical prairies of Thurston and Pierce counties, as well as in other regions of the state (Stinson 2005).

Densities of up to 60/hectare have been reported (Verts and Carraway 2000) for this species.
Current Population Trend:Decreasing
Additional data:
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:It is found in open grassy areas, including pastures, prairies, savannas, and open early seral woodlands and forests (Verts and Carraway 2000, Stinson 2005). This species is fossorial, inhabiting deep, humic volcanic soils (Patton, in Wilson and Ruff 1999). In this species, gestation lasts about 28 days. Females produce one litter of four to six young each year. Young are born in March-June. Pocket gophers are primarily solitary. Predators include owls, coyotes, and bobcats. Pocket gophers are ecologically important as prey items and in influencing soils, microtopography, habitat heterogeneity, diversity of plant species, and primary productivity (Huntly and Inouye, 1988). Diet includes roots, tubers, bulbs and some surface vegetation. Forages from underground burrows. May also forage on the surface of the ground at night or on overcast days. Collects food in cheek pouches and stores it in underground storage chamber.
Generation Length (years):1-2

Threats [top]

Major Threat(s): In Washington, habitat loss to succession, agriculture, and development has eliminated most of the prairie habitat of this species in the south Puget Sound region, and habitat continues to be lost to residential development and other human uses (Stinson 2005). Existing habitat is being degraded by heavy grazing of pastures and the invasion of Scotch broom and other weedy non-native plants (Stinson 2005).

Stinson (2005) reported the following additional information for Washington populations of Thomomys mazama. Pocket gophers may not persist in residential areas due to persecution by trapping, poisoning, and predation by cats and dogs. Gravel mining affects gopher habitat on some private lands. Most occupied habitat on public lands is affected by non conservation uses including military training and recreation. Gopher populations at airports can be affected by the development of airport-related facilities and businesses, and the management of airport grassland. The small size and isolation of most remaining populations of Mazama pocket gopher put them at risk of local extinction, and without increased protection, all but T. m. melanops in Olympic National Park could go extinct. Historically, local gopher populations probably exchanged genetic material by individuals occasionally dispersing through intervening oak woodlands and forest; prairie patches where gophers went extinct would eventually be recolonized. Today, these prairie patches are increasingly surrounded by roads and suburbs that are inhospitable to dispersing gophers. Populations that become extinct are unlikely to be recolonized without reintroductions.

Conservation Actions [top]

Conservation Actions: At least several occurrences of the western pocket gopher are in national parks and other protected habitats.

Errata [top]

Errata reason: This errata assessment has been created because the map was accidentally left out of the version published previously.

Citation: Cassola, F. 2016. Thomomys mazama (errata version published in 2017). The IUCN Red List of Threatened Species 2016: e.T21810A115163696. . Downloaded on 20 September 2018.
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