Prairie dogs, livestock and forage research in the broader context
We have received some questions recently about our research project on prairie dogs in the Thunder Basin National Grasslands and, in particular, why University of Wyoming (UW) is interested in forage quality relative to black-tailed prairie dogs, Cynomys ludovicianus. These questions have come from a recent UW press release that shared some preliminary results that, in 2016, forage quality was found to be higher on prairie dog colonies.
Some folks have expressed concern, and today, I want to just put that single preliminary result into the larger context of our research project. To do that, I need to look at prairie dogs from the agricultural and conservation perspectives and then tell you about our broader questions that we want to answer to ultimately help you.
From an agricultural perspective and as the readers of this publication are well aware, prairie dogs are herbivores and consume the same grass that is needed for livestock. Diet overlap estimates between prairie dogs and cattle has been estimated at about 75 percent, with prairie dog diets being comprised of more than 80 percent grasses. It is suggested that 265 to 335 prairie dogs consume as much grass as one cow.
Moreover, prairie dogs may also simply prune the vegetation at times just to open up the vegetation structure, so they can see predators. As we all are able to very easily see, prairie dogs reduce vegetation on rangelands.
A study from eastern Colorado also indicated that yearling steer weight gains decreased by five and 13 percent when prairie dog colonies comprised 20 and 60 percent of a pasture. Another study, from Oklahoma, did not show a reduction in steer weight gains associated with prairie dog induced reductions of forage, but that study has been criticized for problems with the statistical analysis used.
Studies from the southern portion of black-tailed prairie dog range have shown that cattle preferentially graze on the edge of colonies potentially because of higher forage quality in the colony but higher forage quantity outside of the colony. In other words, prairie dogs and associated forage dynamics can influence livestock distribution.
From a conservation perspective, black-tailed prairie dogs are a wildlife species that is of conservation concern. Current estimates suggest that this rodent only occupies about 10 percent of its historical range today. Moreover, many other wildlife species rely on prairie dogs as a food source or on the habitat that it structures. In 2009, Fish and Wildlife Service reviewed a petition to list prairie dogs under the Endangered Species Act, but it was determined that such protection was not warranted. I also anticipate that black-tailed prairie dogs will be petitioned again in the future.
Wyoming is pretty important for that remaining 10 percent of occupied habitat, and I have heard estimates that Wyoming has about 40 to 50 percent of the remaining black-tailed prairie dogs in the country.
Further complicating the conservation perspective, black-tailed prairie dogs in eastern Wyoming are interspersed within sagebrush habitat that is important for sage grouse. Many questions about how these two wildlife species exist with different habitat structure needs come to mind. In other words, the low structure of prairie dog colonies is not suitable for sage grouse nesting or screening cover and expansion of prairie dogs will have an impact on other wildlife such as sage grouse.
With all of that in mind, we here at UW have been approached by stakeholders in the Thunder Basin, including ranchers, asking for a holistic understanding of prairie dog effects on forage and habitat. Some of the momentum for this is also related to the role of the Forest Service in managing for multiple use.
In other words, as we currently sit today, livestock and prairie dogs will interact on the Thunder Basin National Grassland. That is a guarantee, and thus, we need to understand all we can about that interaction. This public land situation is obviously quite different from management on private land where landowners have more options for managing prairie dogs.
Moreover, much of the research that exists has been done in either Montana, South Dakota or Colorado, but we want to provide producers and managers with local information to guide local decision making. For example, forage quality and quantity has been already studied on National Grasslands in Montana and South Dakota, with the conclusion that reductions in forage quality and quantity changes varied by grassland type and precipitation. The study can be found at naldc.nal.usda.gov/naldc/download.x?id=58171&content=PDF. The authors concluded that the effects of prairie dogs, at certain times and locations, enhanced forage digestibility and nitrogen content with no effect on forage quantity.
At other locations there were negative effects or neutral effects. As the Wyoming Extension range specialist, I say, well, that is great for Montana and South Dakota, but does it happen the same way in Wyoming? Maybe it does, and maybe it doesn’t.
We are currently measuring much more than just forage quality, including forage quantity, grass height, vegetation obstruction, bare ground, litter, plant species composition including shrubs and invasive species and soils characteristics. By collecting this information in Wyoming, we hope to inform you as to when prairie dog densities are not a problem, when they are potentially becoming a problem and the potential consequences for livestock production.
For example, I am aware of colonies that look like a parking lot, but I have also seen colonies with a lot of forage. So, is that a function of prairie dog density, size of the colony, age of the colony, etc.? We need that information, so we can then extrapolate the effects on livestock production relative to the expansion of colonies and the potential consequences. If 10 percent of a one-section pasture is populated by prairie dogs, what is the effect on livestock production capability? What if that increases to 25 or 50 percent of that one section pasture? Then what?
Moreover, by understanding forage quality and quantity, we can then calculate not only the percent crude protein available but also the pounds of crude protein available or lost depending on prairie dog characteristics. Finally, by measuring the physical structure of the vegetation, we can determine other potential consequences.
For example, is grass height too short for cattle consumption? Or, what is the effect on sage grouse habitat if prairie dogs continue to expand? This is important within the larger sage grouse conservation world because, as we all know, livestock are often cast as the problem. However, our research is currently indicating that the extensive livestock grazing in this area is not reducing structural features important to sage grouse, but prairie dog herbivory and expansion seems to reduce grass height and visual obstruction.
It is our hope here in the UW College of Agriculture and Natural Resources to generate research that matters to people out in the state. Our prairie dog-livestock research aims to take a very holistic assessment of this issue and provide details about the intricacies of this complex social and ecological issue. The forage quality component of the project is only one very small part of a much larger project that involves ranchers and other stakeholders.
Finally, getting this information has been quite challenging due to prairie dog expansion and required us to control prairie dogs at certain times. Please contact me any time with thoughts or concerns at firstname.lastname@example.org. Check out my blog ‘Rangelands4u’ at wyoextension.org/rangelands4u.