Rodent Communities in Active and Inactive Colonies of Black-tailed Prairie Dogs in Shortgrass Steppe

Black-tailed prairie dogs (Cynomys ludovicianus) alter shortgrass-steppe landscapes in ways that are expected to affect other mammals. I sampled rodent populations at 31 sites on the Pawnee National Grasslands, Colorado, including 18 active colonies, 6 colonies that had been unoccupied for .6 years (inactive), and 7 grassland sites without prairie dogs (controls). Rodents were livetrapped for 4 consecutive nights at each site between May and August 2004 to estimate relative abundance. I also measured vegetation and habitat characteristics. Northern grasshopper mice (Onychomys leucogaster) and 13-lined ground squirrels (Spermophilus tridecemlineatus) were captured on most ( 87%) of the sites and comprised 40% and 34% of individuals captured, respectively. Species richness ranged from 1 to 6 species, but most sites had only these 2 species. Grasshopper mice tended to be more abundant on colony sites than on controls, although differences were not statistically significant. Ground squirrels were least abundant on active colonies, and most abundant on inactive colonies, followed by controls. Habitat types did not differ in their abundance of any other species or in total rodent abundance; however, active colony area influenced total rodent abundance, with small colonies supporting fewer individuals. Controls supported the most rodent species, in part because these sites consistently had taller grass, which presumably provided habitat and food for less common species (Chaetodipus hispidus, Perognathus flavus, and Reithrodontomys megalotis). In shortgrass steppe, active colonies provided habitat for grasshopper mice, which may be involved in maintenance and spread of plague, but did not support consistently higher rodent species richness than the surrounding grasslands.