Ground Squirrel and Prairie Dog Control in Montana

The Columbian ground squirrel (Spermophilus columbianus), Richardson ground squirrel (Spermophilus richardsoni), and blacktail prairie dog (Cynomys ludovicianus) cause millions of dollars of loss to Montana agriculture each year. Montana's ground squirrel and prairie dog control programs are based upon local organization and operation with technical assistance being provided by the Montana Department of Livestock Vertebrate Pest Control Bureau. The results of field research programs using zinc phosphide, Compound 1080 and strychnine grain baits to control these species are reported. INTRODUCTION Montana, the fourth largest state, has a great deal of variation in topography and climate. In the western portion of the state, roughly defined by the Continental Divide, ranges of timbered mountains are divided by relatively temperate valleys. Glacier National Park and part of Yellowstone Park are found in the western third of Montana. As one travels east of the Divide, smaller mountain ranges are interspersed among the beginnings of the great prairie. Along the Canadian border grainfields grow on table-top flatlands. The rugged Missouri River Breaks and Yellowstone River Valley cut across sparsely populated rangeland in central and eastern Montana. Montana's variety in topography and climate leads to variety in field rodent species. The western intermountain valleys are home for Columbian ground squirrels (Spermophilus columbianus). The Richardson ground squirrel (Spermophilus richardsoni) is found east of the Continental Divide and mostly north of the Yellowstone River. The blacktail prairie dog (Cynomys ludovicianus) lives on rangeland in the eastern two thirds of Montana. Some other species which are indigenous to Montana but rarely cause enough damage to warrant control are the thirteen-lined ground squirrel (Spermophilus tridecemlineatus), the golden-mantled ground squirrel (Spermophilus lateralis), and the whitetail prairie dog (Cynomys gunnisoni). The Uinta ground squirrel (Spermophilus armatus) is found in a small area of extreme southwestern Montana. DAMAGE Ground squirrel and prairie dog damage to food, fiber, and natural resources in Montana is widespread and locally severe. A 1973 survey of USDA Committees for Rural Development, Conservation Districts and other local agricultural groups listed more than $6.5 million economic loss due to damage by these species (Seyler, 1973). The loss was distributed as follows: $1.2 million-Columbian ground squirrel; $4.7 million-Richardson ground squirrel; $0.7 million-prairie dogs. Types of damage frequently seen are: destruction of range and pasture forage, destruction of cultivated crops (most commonly cereal grains), and damage to harvesting equipment. Another type of damage which may be significant but is not well defined in Montana is erosion enhancement. STATE RODENT CONTROL PROGRAM Prior to 1975, Montana's field rodent control programs were administered and supervised primarily by the federal government through the USDA Bureau of Biological Survey and USDI Fish and Wildlife Service. By 1970, however, the federal field rodent control program in Montana was terminated except for the sale of grain baits, gas cartridges and other control materials. The Montana State Legislature, at the request of agriculture producers and recommendation of the Governor's Advisory Council on Rodent and Rabid Skunk Control, enacted legislation giving the Montana Department of Livestock authority to administer and supervise rodent control programs. The Department of Livestock Vertebrate Pest Control Bureau has three district biologists, each serving one third of the state. The biologists' duties are divided among predator, rabid skunk and field rodent control programs. The primary objectives of Montana's field rodent control programs are: 1) Rodent damage assessment; 2) aiding in the implementation and operation of locally operated control programs; 3) public information and education; 4) evaluation of present control methods; and 5) research and development of new control methods. Damage Assessment The collection of scientifically sound economic loss data is as important as it is difficult. Techniques are available for assessing vegetation loss on a given site with exclusion cylinders (Sauer, 1977) and for determining the loss of livestock production due to ground squirrel damage to range forage (Howard, Wagnon and Bentley, 1959). The difficulty arises, however, when trying to establish the economic loss to agriculture on an area-wide basis. Extrapolation of data collected on one site to an entire county or region cannot be done without knowing the precise distribution and