Thomomys talpoides (Richardson, 1828)
Northern Pocket Gopher
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Basis for Listing
Northern pocket gophers are found in North America from southern British Columbia south through the Sierra Nevada range and east through the plains of Canada, Colorado, eastern Nebraska, South Dakota, North Dakota, and the extreme northwestern corner of Minnesota (Verts and Carraway 1999). They have the largest distribution of any species in the family Geomyidae. However, Minnesota is at the eastern edge of the species' range, and the northern pocket gopher has been documented primarily in Kittson County, with one additional occurrence in Marshall County. It was listed as a special concern species in Minnesota in 1984 given its limited distribution in the state, and the potential for persecution due to its similarity to the plains pocket gopher (Geomys bursarius), which is viewed as a pest species in agricultural areas. Since no northern pocket gophers have been documented in Minnesota since 1991, elevating the species' status to threatened is currently being considered.
Northern pocket gophers, like other pocket gophers, are rarely seen, as they spend most of their time underground. Pocket gophers are named for their external fur-lined pouches that are used to carry food. The northern pocket gopher is a medium sized, stocky rodent with a short neck, small, flattened head, small ears, small eyes, large-clawed front feet, and visible incisors. It has brown to yellowish-brown short, soft fur with pale underparts. Adult northern pocket gophers weigh between 60-160 g (2.1-5.6 oz.) and have a total body length of 165-260 mm (6.5-10.2 in.). They resemble other pocket gopher species however, the only other pocket gopher that occurs in Minnesota is the plains pocket gopher. Northern pocket gophers are smaller than plains pocket gophers, and they have smaller forelimbs and smooth or only faintly grooved upper incisors (MacMahon 1999). Adult plains pocket gophers weigh 120-250 g (4.2-8.8 oz.), have a total body length of 225-325 mm (8.9-12.8 in.) (MacMahon 1999; Zimmerman 1999), and have definitively grooved upper incisors.
The northern pocket gopher is present in a variety of open habitats throughout its range. Suitable habitats include agricultural fields, meadows, grasslands, lawns, and partially wooded areas (MacMahon 1999). The species is absent in closed canopy forests due to the need for ground cover vegetation as a food source (MacMahon 1999). It prefers thick, well-drained soils but is more tolerant of other soil types than other pocket gopher species, and it can be found in rocky soils or soils with a high clay content (MacMahon 1999). In Minnesota, both pocket gopher species inhabit the clayey soils near the Red River, but plains pocket gophers are believed to out-compete northern pocket gophers in lighter, sandy soil areas elsewhere in the state.
Biology / Life History
Northern pocket gophers are active year-round. They are territorial and solitary except during the breeding season. The breeding season for the northern pocket gopher is geographically variable but occurs sometime in the spring between March and June (MacMahon 1999; Verts and Carraway 1999). Gestation lasts 18-20 days after which a litter of 4-7 young is born (MacMahon 1999). The young are weaned after 40 days but stay with their mother until 6-8 weeks of age, and are not fully-grown until 3-6 months of age (MacMahon 1999; Verts and Carraway 1999). Only 1 litter is produced each year. The lifespan of a northern pocket gopher may be up to 6 years under ideal conditions, but is more likely 1.5-2 years in the wild (MacMahon 1999). Predators of this species include owls, hawks, badgers (Taxidia taxus) and other weasels (Mustela spp.), foxes, coyotes (Canis latrans), skunks, bobcats (Lynx rufus), and snakes.
Conservation / Management
The northern pocket gopher is widely distributed in North America, however they have been documented in only two counties in extreme northwestern Minnesota. These locations constitute the eastern range limit of the species in the United States. Based on trapping records, northern pocket gophers appear to have declined in the state. The major causes of the decline are thought to include habitat loss, persecution by humans, and competition with the more common plains pocket gopher. Much of the habitat for this species has been converted to farmland, which destroys underground burrows. Compounding this problem is the view of pocket gophers as unwanted pests in agricultural areas because of the mounds of soil they create in fields and pastures. Mounds and runways cause potential damage to livestock and machinery and may lead to reduction of crop yields. Because of this, pocket gophers are controlled by poisoning and trapping, and some counties still carry a bounty of $0.70 to $2.00 per pocket gopher. Unfortunately, no distinction is made between the more common plains pocket gopher and the rare northern pocket gopher. In 1993, over 33,000 pocket gophers were turned in for bounties in counties where northern pocket gophers are known to live. Unfortunately, there is no record of which species were collected.
Conservation Efforts in Minnesota
Surveys for northern pocket gophers have been conducted by the Minnesota Biological Survey for several years. Known populations should be monitored periodically to determine changes in distribution and abundance and additional surveys should be conducted to assess the statewide distribution of the species.