National Park Service


Date of this Version



Natural Resource Report NPS/AGFO/NRR 2014/883 / NPS 165/127182, November 2014: x, 64 pages

Published by the United States Department of the Interior, National Park Service, Natural Resource Stewardship and Science, Fort Collins, Colorado

Also available at:

Please cite this publication as: Licht, D. S. 2014. Restoration of Bison (Bison bison) to Agate Fossil Beds National Monument: A Feasibility Study. Natural Resource Technical Report NPS/XXXX/NRTR—2014/XXX. National Park Service, Fort Collins, Colorado.


United States government work. Public domain material.


Executive Summary

Agate Fossil Beds National Monument is a 3,057-acre park located in western Nebraska. The unit is comprised of northern mixed-grass prairie vegetation, typical of the Northern Great Plains. Weather, fire, and grazing are generally considered to be the ecological drivers of prairie ecosystems and critical for prairie health. However, grazing has essentially been absent since the 1960s. In 2014, a Department of the Interior report explicitly listed the park as a high priority for bison restoration. This report evaluates the feasibility, management options, benefits, and challenges of restoring bison to Agate Fossil Beds National Monument.

A potential bison pasture encompasses about 2,676 acres within the park, essentially the area east of Highway 29. Assuming 2,676 acres are available to bison, a forage intake rate of 2.667%, a natural sex and age structure for the herd, an average bison weight of 1,000 pounds, and an allocation of 33% of annual plant productivity to bison consumption, the park could support 166 bison in the fall in a normal-precipitation year including calves, or about 136 yearlings and adults. Using the same assumptions the dry year carrying capacity is 129 animals and the wet year carrying capacity is 219 animals (including calves). Changes in other assumptions and objectives result in different modeled carrying capacities ranging from 52 to 443 animals, demonstrating the latitude available to management. Using the assumptions listed above, if the portion of the park that encompasses the visitor center, park housing, and a private in-holding is excluded from the bison pasture (an area of about 300 acres) then the carrying capacity is reduced to about 147 bison in the fall.

If bison were restored to the park they would occur in a closed system absent of natural predation to affect population growth. Assuming a starting population of 40 yearlings (at a 50:50 sex ratio), the herd would reach carrying capacity about 9-11 years later. Numerous anthropogenic options are available to manage the herd size; however, the most conventional and feasible consists of the park periodically rounding up and transferring live animals to other entities such as Native American tribes. This approach is used by many NPS units with bison. Tradeoffs exist between the frequency of the removal operations and the quantity and age-sex classes of the animals removed in a cull. For example, assuming a goal of a long-term average population of 166 bison in the fall, an annual cull of 70% of the yearlings (about 23 animals) would maintain the herd at that level as would a cull conducted every third year that removed 40% of all age and sex classes (removing about 81 animals total). The greater the duration between culls the greater the variability in herd size, e.g., a cull every fifth year that removes 60% of the herd results in a population that fluctuates between 99 and 202 animals. Other considerations in selecting a culling strategy include ecological objectives, bison genetic goals, available funding and infrastructure, drought, and availability and desires of the recipients of the bison.

The conservation of bison genetics is a high priority within the NPS. Frequent smaller culls better conserve bison genetics as the population does not experience the deep nadirs caused by the removal of large numbers of animals necessitated by less frequent culls. The larger the herd the better genetic diversity is conserved, all else being equal. Genetic diversity could be better conserved if an Agate Fossil Beds herd was managed as a metapopulation with other NPS herds. The park could also choose to manage bison in partnership neighbors, one of whom owns about 5,000 acres. Such a partnership would greatly increase the size of the herd, ecological function, and genetic conservation.

The potential benefits of restoring bison to Agate Fossil Beds National Monument include:

1) restoring a native species to the park,

2) restoring an ecological process to the park that enhances the conservation of biodiversity,

3) improving visitor experience and understanding,

4) benefitting local communities via increased tourism,

5) restoring a Native American ethnographic and cultural resource,

6) contributing to meeting DOI and NPS bison goals,

7) establishing a metapopulation that contributes to agency and global conservation of bison genetic diversity,

8) establishing a genetically pure bison herd (assuming the needed technology is completed),

9) establishing a satellite herd that provides redundancy in case of a catastrophe to another NPS herd(s),

10) being a repository for Yellowstone National Park or other park bison, if needed.

The challenges to bison restoration at the park include the cost and potential impacts of bison-associated infrastructure and maintenance, the need to hire staff with natural resource expertise, and the need to foster support within the agency and with stakeholders. Depending on the location of the bison pastures the park may also need to address private inholdings within the park administrative boundary, impacts on paleontological resources, issues associated with a county road, and impacts to the park administrative areas and structures. The small size of the park makes a well-designed prescribed fire program and an active vegetation monitoring program especially important to assure park goals are being met.

This feasibility study primarily provides a scientific evaluation of restoring bison to Agate Fossil Beds National Monument. Ultimately a full evaluation that considers other concerns and impacts (e.g. cultural resources) would need to be conducted as part of an environmental assessment and management plan. This report tries to facilitate that process wherever possible by analyzing and presenting a range of values. An environmental assessment would also need to consider action alternatives that were not fully vetted here, such as introducing cattle in lieu of bison for purposes of restoring the grazing process. From an ecological and conservation perspective there would be many benefits to restoring bison to the park, and it would be very feasible.