B lack ta i l p r a i r i e dogs (Cynomys ludovic ianus) were more abundant (P < 0.01) in areas o f southwestern South Dakota heavi ly grazed by c a t t l e than in areas where c a t t l e were excluded. Results suggest tha t per iod ic exclusions or reduced c a t t l e stocking ra tes , in combination w i th cont ro l programs, help regulate p r a i r i e dog populat ion increase and expansion as indexed by burrow counts. B lack ta i l p r a i r i e dogs are abundant and widespread on the Great P la ins. Large populat ions of p r a i r i e dogs are o f ten considered pests by ranchers and range managers because they consume forage plants s i m i l a r to those eaten by c a t t l e (Hansen and Gold 1977) and t h e i r burrows can be a hazard to l i ves tock . As a r e s u l t , much money has been spent on p r a i r i e dog c o n t r o l . Some research suggested tha t b l a c k t a i l p r a i r i e dogs were most abundant in areas i n tens i ve l y grazed by l i ves tock (Koford 1958, Uresk and Bjugstad in press) . B lack ta i l p r a i r i e dogs inhab i t areas where vegetat ion height was reduced by c l i p p i n g unpalatable plants to ground leve l (Koford 1958). In tensive c a t t l e grazing has been associated wi th an increase in b l a c k t a i l p r a i r i e dog populat ion expansion. This paper presents the resu l ts o f a study which compared b l a c k t a i l p r a i r i e dog burrow dens i t ies on s i tes tha t have been i n tens i ve l y grazed by c a t t l e to adjacent s i t es where c a t t l e were excluded. The study area was located in southwestern South Dakota, on the Buffalo Gap National Grasslands. The por t ion o f the Grasslands examined was in Conata Basin, a lowland area surrounded by b l u f f s and mesas. Vegetation o f the basin was p r imar i l y buf fa lograss (Buchloe dac ty lo ides ) , blue grama (Bouteloua q r a c i l i s ) , western wheatgrass (Agropyron sm i tnT i ) , s ca r l e t globemallow (Sphaeralcea coccinea) , and p ian ta in (PTantago patagonica). METHODS Three cattle exclosures, approximately 0.2 ha each, were established in 1975 on a prairie dog town that had been grazed by both cattle and prairie dogs. These exclosures were grazed by prairie dogs only. Three adjacent sites were grazed by both prairie dogs and cattle. Utilization of forage was greater than 60 percent on sites grazed by cattle and prairie dogs. All burrows were counted in each of the 6 sites to develop an index of prairie dog population density. Aerial photographs taken in 1974 provided pretreatment burrow counts for all 6 sites. Burrow counts were made in the field, during 1978 and 1979, to determine trends in prairie dog population densities on cattle plus prairie dog and prairie dog only sites.