Population Recovery of Black-Tailed Prairie Dogs following Control with Zinc Phosphide

Abstract

This study evrlluted the efficacy of 2% zinc phosphide grain bait as a control agent for black-tailed prairie dogs (Cynomysludovicignus) and the rate at which prairie dogs returned to treated areas. Visual counts of prairie dogs closely corresponded to actual population trends and were chosen as the technique to evaluate changes of prairie dog numbers. Treatment of al1 of 2, and portions of 5, prairie dog colonies with zinc phosphide grain bait between 30 July and 25 August 1978 resulted in an average of 85% (range 65 to 95%) reduction in prairie dog numbers. Rest results were obtained in the 2 colonies treated totally. The 2 colonies treated along the perimeter had the lowest percentage decrease in numbers of prairie dogs and were among the treatment types with the fastest population recovery. Prairie dogs returned to pretreatment levels within 1 year posttreatment at 1 colony. After 2 years posttreatment, 3 other colonies were approaching pretreatment population levels. Three to 5 years posttreatment appeared to be needed to obtain pretreatment numbers in the 2 colonies treated totally. Control of black-tailed prairie dogs (Cynomys ludovicianus) is often considered economically feasible because it is thought to provide more forage to livestock. Marsh (1967) considered a 90% reduction in rodent populations necessary to achieve satisfactory relief from economic damage. In general, studies have found grain baits treated with strychnine or zinc phosphide to be effective at reducing prairie dog numbers to levels considered efficacious (Tietjen 1976, Sullins 1977,1980a,b, Tietjenand Matschke 1982). There is little information available, however, to indicate how rapidly prairie dogs return to treated areas following substantial population reductions. Deer mice (Peromyscus maniculatus) invaded treated areas so rapidly as to negate any economic benefits of control (Gashwiler 1969, Pank and Matschke 1972, Sullivan 1979). The rate of population recovery following control with toxicants is important in the assessment of the cost/ benefit ratio of such projects (Collins et al. 1984). The purpose of this study was to evaluate the efficacy of zinc phosphide grain bait as a control agent for black-tailed prairie dogs and to determine the rate of population recovery in treated areas.