In a new large-scale study of wild bison genetics, a team of scientists funded by the U.S. National Park Service and led by the Wildlife Conservation Society (WCS) has identified practical actions to maintain the genetic health of bison herds on federal lands, setting a foundation for the successful long-term conservation of wild bison. Findings indicate that increasing the actual or effective size of existing herds, establishing large herds, or the careful exchange of individual bison between herds, is needed to maintain the genetic diversity of wild bison.

Findings of the study helped lay a foundation for the new U.S. Bison Conservation Initiative announced today by Secretary of the Interior David Bernhardt. The cooperative initiative will coordinate conservation strategies and approaches for wild American bison over the next 10 years. “Interior is uniquely positioned to lead the way for shared stewardship of this iconic American species,” said Secretary Bernhardt. “This 10-year plan will guide our collaboration with states, tribes, private conservationists and managers across public lands to advance conservation efforts and honor iconic wild bison.”

Most bison herds on federal lands are projected to lose genetic diversity without some form of genetic management. Genetic diversity underpins the ability of species to adapt to changing environmental conditions, and strengthens resilience to future environmental challenges such as outbreaks of new diseases.

Cynthia Hartway, a biologist with the Wildlife Conservation Society and lead author on the study said: “Plains bison are an iconic species, important both culturally and ecologically. This study is unique in that multiple state, federal and non-profit groups recognized the potential threat that genetic diversity loss posed to bison, and came together to investigate and ensure we’re doing all we can for their long-term conservation and survival.”

North American plains bison (Bison bison bison) once numbered in the tens of millions with a range that extended from northern Mexico to central Canada. By the end of the 1800s, a combination of commercial hunting, novel diseases, and systematic extermination had driven plains bison to the brink of extinction. By 1900, fewer than 1,000 bison remained, with under 100 animals remaining in the wild. WCS’s Bronx Zoo helped save the species from extinction thanks to reintroduction efforts in the early 1900s. Today an estimated 20,000 plains bison live in conservation herds managed by Tribes, non-profits, and government agencies across North America, with over half living on U.S. Department of Interior lands. Most of these herds are fenced and relatively small, with little to no natural movement of individuals between herds. Small, isolated populations are more vulnerable to genetic diversity loss through the process of genetic drift. 

To evaluate the current genetic diversity within herds living on public lands and to determine whether coordinated genetic management is necessary to maintain diversity, the scientists worked with the U.S. National Park Service, the Fish and Wildlife Service, Parks Canada, Arizona Game and Fish, Utah Division of Wildlife Resources, and Alaska Department of Fish and Game to gather and analyze genetic data from more than 1,800 bison from 16 herds within the U.S. and two from Canada. They then projected how current conditions (current herd sizes with little to no exchange of bison between herds), and alternate management actions (including the coordinated exchange of bison between herds), affect the genetic diversity of herds over time. They found that increasing the actual or effective size of herds and periodic transfers of bison between genetically unrelated herds can conserve genetic diversity into the future.

Study co-author Brendan Moynahan, a Science Advisor for the National Park Service, said: “This cooperative research demonstrates how diverse partners can come together to directly address the important conservation issues faced by federal bison managers. Working together, we’ve set the stage to not only more effectively conserve bison genetic diversity, but to also support the ecological and cultural restoration of the wild American bison.” 

Co-author Lee Jones from the U.S. Fish and Wildlife Service said: "Building on a century of bison conservation success through innovative partnerships, this new research provides a solid, science-based foundation for restoring gene flow among the Department of Interior’s bison conservation herds."

WCS plans to extend the project to examine additional conservation herds from throughout the United States, Canada, and Mexico, and WCS’s Bronx Zoo is currently working to establish a large herd of bison for rewilding programs. Cynthia Hartway: “This project provides a great framework for developing partnerships across political and social boundaries that can ensure the genetic health of not just individual herds, but the long-term survival of wild bison as a whole, and fostering broader ecological and cultural restoration of bison.”

The study titled “Long-term Viability of Department of the Interior Bison Under Current Management and Potential Metapopulation Management Strategies” was conducted in partnership with the U.S. National Parks Service can be found here. The study was published by the U.S. Department of the Interior and authors include Cynthia Hartway (Wildlife Conservation Society), Amanda Hardy (National Park Service), Lee Jones (US Fish and Wildlife Service), Brendan Moynahan (National Park Service), Kathy Traylor-Holzer (International Union for the Conservation of Nature), Blake McCann (National Park Service), Keith Aune (formerly of Wildlife Conservation Society), Glenn Plumb (International Union for the Conservation of Nature).