The impact prairie dogs have on livestock grazing on Western rangeland has been a confounding issue for both conservationists and ranchers, and part of the problem has been a lack of data that clearly measure the effect. A collaboration between scientists at Colorado State University and the USDA Agricultural Research Service, published in the November issue of the journal, "Frontiers in Ecology and the Environment," has for the first time quantified these impacts in terms of cattle weight gains and dollar amounts.
Prairie dogs play an important role in maintaining the diversity of grassland species, including the preservation of the endangered black-footed ferret. Ranchers typically are wary of prairie dogs because they can reduce the weight gains of livestock by feeding on the same grasses, according to researchers who collaborated on the study. However, the study found that the effect prairie dogs have on livestock weight gains depends on the size of prairie dog colonies on the pastures. Only the largest colonies reduced the estimated value of livestock weight gains, the study found.
"There has never really been an impartial body of evidence that can be used by both ranchers and conservationists which details, in weights and dollar amounts, the effects of prairie dogs on cattle grazing on the same pastures," said Mike Antolin, a professor in the Department of Biology at Colorado State and co-author of the study.
Using the data established by the study, a land manager can take these findings into account by decreasing the amount of livestock grazing in a pasture when the number of prairie dogs increases, thereby ensuring that livestock better retains their value at market.
For example, pastures with 20 percent of the area occupied by prairie dogs reduced the estimated value of the livestock weight gain by $14.95 per steer (about 5.5 percent); whereas livestock weight gain in pastures where prairie dogs occupied 60 percent of the area was reduced by $37.91 per steer (about 13.9 percent), the study found.
"It would be hard to quantify a noticeable change in the weights of livestock coming from pastures where prairie dogs occupy less than 5 percent of the area," said Jim Detling, a Colorado State biology professor who collaborated on the study.
The study is part of long-term studies of pastures, prairie dog colonies and livestock spearheaded by Rangeland Scientist Justin Derner of the USDA, Agricultural Research Service, Central Plains Experimental Range, or CPER, located in the north-central Colorado plains near Nunn, Colo. The research site was established in the late 1930s after the Dust Bowl to research improved management practices of fragile grasslands. The CPER works in collaboration with the NSF-funded Shorgrass Steppe Long Term Ecological Research project at Colorado State University.
"The research we’ve conducted doesn’t unilaterally show prairie dogs are bad for cattle but doesn’t unilaterally show that prairie dogs are benign to cattle," Antolin said. "There are still going to be arguments about prairie dog management practices, but this research provides data that are useful for both sides of the issue."