Thomomys talpoides (Richardson)
Northern pocket gopher
Description.—The pocket gopher is a fossorial animal, being but slightly less adapted to an underground existence than the moles. The body is stout, the legs short and the head broad. The tail is short, sparsely haired, cylindrical and blunt-ended. The fur is soft and dense. The eyes are small and the ears tiny and naked. The incisor teeth are external, being separated from the mouth cavity by a furry strip of skin. Like the pocket mouse and kangaroo rat, the pocket gopher possesses external, fur-lined cheek pouches. The openings of these begin just below and posterior to the nostrils, sweep out and down in a semicircle, and end at the chin posterior to the base of the lower incisors. They extend laterally to the shoulders and easily accommodate a fifty-cent piece.
Fig. 95. Northern pocket gopher (Thomomys talpoides yelmensis), from two miles southwest of Tenino, Washington, January 28, 1941. (Fish and Wildlife Service photo by Victor B. [Scheffer], No. 1133.)
The family Geomyidae is composed of eight genera, so similar in appearance that the name "pocket gopher" is applied to all of them. The family is confined to North and Central America. Three genera occur in the United States but only one, Thomomys, occurs in Washington. Thomomys is restricted to western North America where it ranges from central Canada south to the southern edge of the table land of Mexico.
Several hundred kinds of Thomomys have been described and as systematic work with this genus has been continued, more and more kinds, originally thought to be species, are found to intergrade and to be only subspecies. All of the 17 kinds of pocket gophers occurring in Washington belong to a single species.
The pocket gopher is principally nocturnal or crepuscular but sometimes it is active at midday, especially if the day be dark and cloudy. Pocket-gopher activity is indicated by fresh mounds of earth on the surface of the ground. Rarely, an observer may see movement of plants as the gopher molests the roots of the plants, or even see the head and shoulders of an animal that partly emerges from an open burrow. The ordinary gopher mound consists of less than a cubic foot of earth. The earth is forced up from a single opening and usually is pushed out in one direction. In consequence it forms in a fan-shaped pile about the opening, and the last load forms a circular plug above and to one side of the burrow opening. When so much earth has been forced out of one opening that expulsion of additional loads of earth is overly difficult, the burrow is extended slightly to one side, or even extended into the newly formed mound, and another fan formed. Usually not more than three coalesced fans form a mound, but where the soil is exceedingly soft and fluffy, hundreds of fans may form a composite mound and the one mound may include a cubic yard of earth. Large composite mounds probably are formed gradually over a period of weeks or even months.
The earth in a fresh gopher mound is usually "scratched," and gives the appearance of having been sieved. Pebbles weighing more than 100 grams are included in material ejected from burrows. The entrances to the burrows of gophers are usually solidly plugged with earth. The plug may be from a few inches to more than a foot in length. At times a burrow entrance may appear to be open, but in such cases investigation will usually reveal it to be plugged some distance back—sometimes several feet.