Black-Tailed Prairie Dog Colony Dynamics in South Dakota Over a 10-Year Period

Between 1968 and 1978, aerial photography was used to monitor distribution of blacktailed prairie dog (Cynomys ludovicianus) colonies on a 400-square mile area in South Dakota, including parts of Buffalo Gap National Grassland, Pine Ridge Indian Reservation, and Badlands National Monument (now Badlands National Park). Aerial photographs were taken of the study area in 1968 and annually from 1974 through 1978 at a scale of 1:20,000 (1968) and 1:15,840 (19741978). Prairie dog colonies were identified on the photographs, outlined, and the outline transferred to USGS topographic maps for colony size measurements. This technique reliably detected changes in prairie dog colony numbers, size and distribution. Although there was limited use of prairie dog rodenticides early in the study, the land area occupied by prairie dog colonies increased by approximately 28.4% over the 10-year period. Between 1968 and 1974 area occupied by prairie dog colonies increased from 1154 ha (1.4% of the area) to 5890 ha (7.1%). By 1978, prairie dog colonies occupied 14023 ha (16.9% of the area). The number of colonies increased from 110 in 1968 to 344 in 1974 and 508 in 1978, with many colonies being assimilated during colony expansion. Prairie dog colony expansion rates were significantly lower on the Badlands National Monument (BNM) than on the Buffalo Gap National Grasslands, private lands, and Pine Ridge Indian Reservation. The BNM is ungrazed by livestock (cattle), while most other rangelands in the study are a grazed annually by livestock at moderate to high stocking rates. Standing vegetation around prairie dog colonies in the National Monument was noticeably greater than around colonies elsewhere in the study area, suggesting that vegetation impacts from annual livestock grazing significantly increased colony expansion rates outside the BNM. Modifications to the grazing regime may improve rangeland condition, particularly during drought years when the rangeland is under stress, and could slow or eliminate prairie dog colony expansion.