Mammalogy class field trip to Wind Cave National Park, April 1, 2005

Wind Cave Park in winter.

This field trip was attended by Lee McDowell and Valerie Janis. Conservation biology instructor Steve Platt and Mammalogy class instructor Jim Taulman were also present. Wind Cave wildlife biologist Dan Roddy and botanical ecologist Marie Curtin provided us with a very thorough presentation of the ecology of several of the mammal species at the park and the state of the grassland forage that sustains the herbivore grazers and browsers. Currently Wind Cave protects and supports populations of some 450-500 bison, 150 mule and white-tailed deer, 60 pronghorn antelope, and an enlarged population of some 800 elk, as well as about 2000 acres of prairie dog towns.

Wildlife Biologist Dan Roddy explains aspects of ungulate ecology to Lee, Steve, and Valerie.

Marie described the three main vegetation issues currently being addressed through research and monitoring at the park: 1) protection of hardwood species that serve as important nutritional browse for ungulates, 2) control of noxious and introduced weeds that tend to outcompete native grasses, and 3) enhancing the vigor of native grasses in order to provide abundant resources for the grazing mammals here.

Of the 20% of the plants in the park that are exotic, many of those are troublesome or noxious weeds. Four of the eight thistle species are non native plants. Canada thistle is a particularly problematic species that park biologists have had some success controlling with the stem gall fly, a host specific insect parasite. Leafy spurge is treated with a specific flea beetle that attacks it and consumes leaf tissue. Other non native weeds, such as spotted knapweed are attacked by the stem mining weevil and other biological insect control parasites.

Botanist Marie Curtain describes a project in which some 45 acres have been fenced to protect an aspen grove that was in danger of being overbrowsed and eliminated.

The capacity of the park to support its ungulate population (the bison, pronghorn antelope, mule deer, white-tailed deer, elk) as well as other important herbivores like the black-tailed prairie dog, is determined by sampling grasses during summer and estimating total grassland forage availability.

Woody browse important to ungulates at the park.

About 31 million pounds of foods are provided by the grasses in the park during the growing season, but hot all of that is available to the wildlife there. Ecologists know that it is important to allow about half of the grasses to remain ungrazed in order to maintain adequate ground cover and allow the grass species to reproduce and sustain the health of the grassland community. And about half of the forage available for grazers may be lost to various environmental factors, such as insect infestation, damage by trampling, or hail storms or other weather.

A summer hail storm on the prairie will cause damage to grasses and even may harm birds and other wildlife.

So only about 25% of the grassland forage produced each summer is available to be eaten by the mammal populations in the park. This quantity of food amounts to about 10,000 animal use months (AUM), a unit that allows evaluation of the ability of the park’s grassland to feed the animals living there.

Research ongoing at the park will determine the number of AUMs of forage needed by individual animals of each of the grazing species in the park. That will allow accurate estimation of the carrying capacity of the park for each species. It has already been determined that a bison requires about 1.2 AUM of forage and there are currently in the range of 450-500 bison in the park. If biologists decide that the park has more bison than it can support, individuals will be sold to tribes or individuals with other private herds.

Bison cow and calf at the park.

The Wind Cave bison have been tested genetically and determined to be a pure population; they have no ancestral history of interbreeding with domestic cattle, as do most other bison herds in the United States. The only other pure bison herd is the one maintained at Yellowstone National Park. Wind Cave also attempts to promote the continuation of this pure bison pedigree as it allocates surplus animals to be raised in private herds.

In addition, the bison herd is currently in excellent health. The last known case of Brucellosis was found in 1984 and the herd has been disease free since then.

Dan and Marie told us about the situation with chronic wasting disease (CWD) in the deer and elk herds in and around the park. Apparently the disease was first detected in an elk population brought to the Casey ranch adjacent to the park, where the first elk with CWD were detected in the late 1990s. All 250 elk in that herd were killed and their carcasses burned and buried. Since then about 3 additional wild elk have been found with CWD. Research conducted in the park on deer by Kristin Schuller, a graduate student at South Dakota State University, looked at tissue samples from almost 100 animals and found about 4% of those deer to be infected. As long as CWD incidence does not rise above those levels, which are about normal in other studied deer and elk populations elsewhere, the disease probably is not a significant threat to local deer and elk populations.

The elk population in the park has grown to about twice the size that is desired. Since CWD has been found to occur in local elk, even though the incidence is low, elk cannot be live shipped to other areas. The best strategy for dealing with this large population is currently being studied and a management plan will be created with professional and public input.

Looking like part of the grassland, this porcupine travels cross country to another forest patch.

We also discussed the role of prairie dogs at the park and in the shortgrass prairie ecosystem. While prairie dogs clearly clip and eat much of the grass around their burrows, this clipping also invigorates grasses to grow and produce a more nutritious shoot. The same effect is seen in suburban lawns that are mown regularly.

Dan discusses the role of prairie dogs in the grassland ecosystem with Valerie, Steve, and Lee. Valerie is planning on doing a study of prairie dog ecology and habitat use on the Pine Ridge reservation for her master’s thesis.

Prairie dogs provide a wide range of ecological benefits to the grassland and are an essential component of the shortgrass prairie ecosystem. Their burrows provide needed refuges and nesting habitat for a diverse community of species, such as burrowing owls, snakes, amphibians, insects, and others. In addition, prairie dogs are an important food resource for such predators as raptors, badgers, coyotes and foxes, black-footed ferrets, and snakes.

Prairie dogs provide valuable ecological benefits to the shortgrass prairie community.

The Wind Cave National Park biologists understand the role of prairie dogs in the South Dakota grasslands and are developing a management plan to address the proper way to allow this species to live in harmony with the other herbivores in the park.

Sunset over Wind Cave National Park.

Our visit with biologists Dan Roddy and Marie Curtin was very enjoyable and instructional. This park is providing an example of how to properly manage our native wild mammals in South Dakota on a sustainable basis and with retention of grassland health and productivity. Research is being conducted on a continuing basis to better understand population dynamics of mammal species occurring here and to provide for their habitat and food requirements.

Oglala Lakota College has acquired a small herd of bison and is attempting to apply proper management techniques in a bison recovery project. The expertise and experience available at Wind Cave National Park can help to ensure the success of the effort at OLC.

Bison being released into the Oglala Lakota College bison pasture near Kyle, SD.