Identifying destructive rodents

Throughout Lake County many landowners are reporting damage to range, pasture and lawns by rodents of various types. Conditions have been favorable to the increase in populations of voles, pocket gophers and Columbian ground squirrels. Each species can be identified by the damage they cause.

Voles, also called meadow mice or field mice, are compact rodents with stocky bodies, short legs and short tails. They usually are brown or gray, though many color variations exist. Voles may cause extensive damage to orchards, ornamentals and tree plantings due to their girdling of seedlings and mature trees, which usually occurs in fall and winter. The most easily identifiable sign of voles is an extensive surface runway system with numerous burrow openings. Runways are one to two inches in width. Vegetation near well-traveled runways may be clipped close to the ground.

Pocket gophers are the rodents that leave soil mounds on the surface of the ground. Unlike ground squirrels, which have open holes leading to their tunnel system and are often seen outside their holes, pocket gophers spend almost all their time in their sealed underground tunnel systems. The mounds they create are usually fan shaped and tunnel entrances are plugged, keeping intruders or predators out of the burrows. Pocket gophers can cause considerable damage to agricultural land, as well as lawn and gardens, but there are several effective ways to control and prevent the destructive results of their prolific burrowing.

Columbian ground squirrels are easily distinguished from other Montana ground squirrels by their larger size and distinctive coloration. An average adult weighs more than a pound. Its head and body measure 10 to 12 inches in length and the tail is three to five inches long and tends to be bushy, particularly when excited. Reddish brown fur is found on the nose, forelegs and hindquarters. The back and upper limbs are mottled gray and brown. Columbian ground squirrels don’t cause damage during the fall and winter because they hibernate for six months each year and are usually active between late March and August. Ground squirrels dig large burrows, leaving a hole 5 to 6 inches in diameter with large mounds of soil surrounding the entry hole.

For all three rodent species, a variety of control methods need to be employed to effectively reduce their population. Depending on the location of the rodent infestation and resources available, an integrated control approach can include such things as habitat modifications, flood irrigation, repellents, mechanical control, trapping and toxicants. If you are experiencing rodent problems, contact the MSU Lake County Extension Office for control suggestions by calling 676-4271 or email

– Jack Stivers is the Lake County Extension Agent for Montana State University

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