Yellowstone bison are managed differently than other wildlife that migrate or disperse outside the park because the Secretaries of Agriculture and Interior and the Governor of Montana signed a court-mediated agreement in 2000 that provided guidelines for limiting bison abundance and distribution in Montana.
The state of Montana allows some bison to migrate outside Yellowstone National Park and occupy suitable winter range near the park boundary, and tolerance on additional range may occur in the future. However, mass migrations of many hundreds of bison out of the park have, at times, upset state and local governments and many private landowners and cattle operators.
Yellowstone bison have been chronically exposed to the non-native disease brucellosis that can be transmitted to cattle and cause abortions. As a result, bison are not allowed to move unimpeded into cattle-occupied areas in Montana.
Brucellosis is a non-native disease that was likely introduced to bison and elk in the greater Yellowstone area by cattle some time before 1917. It is detrimental to Yellowstone bison because it induces abortions and reduces pregnancy rates.
Also, the risk of brucellosis transmission to cattle devalues bison as wildlife outside Yellowstone National Park, limits tolerance for their migration to essential low-elevation winter ranges in Montana, and prevents relocations elsewhere to enhance conservation of the species.
Wildlife managers in the greater Yellowstone ecosystem would certainly like to eradicate or substantially suppress this non-native disease, but the reality is that eradication or even a substantial reduction of brucellosis in bison and elk is not attainable at this time without taking extremely intrusive management actions that would drastically affect their demography and behavior, and infuriate a large portion of the American public.
Future planning efforts will consider whether or not brucellosis suppression will continue as part of the management of Yellowstone bison.
Cattle operations in the Gardiner and Hebgen basins of Montana vaccinate all calves and most adults with vaccine strain RB51, which is the best available vaccine for bovine brucellosis.
Strain RB51 vaccine reduces abortions and further transmissions from vaccinated cattle that subsequently become exposed to, and infected with, brucellosis bacteria.
However, the vaccine does not protect cattle from being infected after exposure to infectious amounts of bacteria deposited by infectious bison or elk. Thus, vaccinating cattle will not eliminate the potential for brucellosis infection from wildlife.
Eradication of brucellosis is not feasible at this time due to our limited understanding of wildlife immune responses to disease suppression actions such as vaccination, the absence of an easily distributed and highly effective vaccine, limitations of current diagnostic and vaccine delivery technologies, potential adverse consequences (e.g., injuries, changes in behavior) to iconic wildlife species from intrusive disease suppression activities, and chronic infection in elk which are widely distributed and could re-infect bison.
Even a substantial decrease in brucellosis prevalence will be difficult in the coming decades given current technology and existing conditions.
- the absence of an easily distributed and highly effective vaccine (e.g., 10-15% reduction in infection; short duration of immune protection; cannot vaccinate in second-half of pregnancy);
- limitations of current diagnostic and vaccine delivery technologies (inconsistent vaccine hydrogel formulation; short rifle range; no rapid diagnostics for live animals);
- effects of bison nutrition, condition, and pregnancy/lactation that lessen protective immune responses;
- bison mating behavior, migration patterns, and hunting seasons that make it difficult to treat sufficient females each winter to have a lasting effect on brucellosis suppression;
- potential adverse consequences (e.g., injuries, changes in behavior) to wildlife and visitor experience from intrusive brucellosis suppression activities (e.g., capture, remote vaccination);
- our limited understanding of bison immune responses to brucellosis suppression actions such as vaccination; and
- chronic infection in elk which are widely distributed and would almost certainly re-infect bison.
During the court-mediated negotiations that led to the Interagency Bison Management Plan, the state of Montana requested that the National Park Service (NPS) implement an in-park brucellosis vaccination program as a stipulation for the state to consider providing greater tolerance for bison on suitable public lands outside the park. The state offered to adaptively adjust their tolerance for bison in exchange for a progressively more comprehensive vaccination program to reduce the brucellosis infection rate in Yellowstone bison.
- Increased winter habitat available outside the park for migratory bison.
- Increased availability of year-round habitat outside the park for migratory or dispersing bison.
- Decreased abortions due to a non-native disease.
- Reduced transmission of the disease among bison.
While NPS policy does not specifically mention vaccination, policy describes actions for “animal population management.” The use of vaccines for wildlife management and conservation purposes is not a new practice in National Park Service units. Contraceptive vaccines have been used in a variety of national park units since the 1970's.
Units have conducted vaccination programs on free-ranging wild animals to control abundance of horses (Assateague Island National Seashore), feral donkeys (Virgin Islands National Park), Tule elk (Point Reyes National Seashore), and white-tailed deer (Fire Island National Seashore).
- The NPS may intervene to manage populations of native species when such interventions will not cause unacceptable impacts to the population or to other components and processes of the ecosystem.
- The NPS may manage exotic species if control is prudent and feasible, and the species interferes with natural processes and the perpetuation of native species
- Vaccination of bison would be considered intervention that does not cause unacceptable impacts to the bison population or ecosystem since the aim of the program is to cause a decrease in the abundance of an exotic or non-native disease.
Current bison management plans do not propose to eradicate brucellosis from bison. Thus, implementation of vaccination does not mean the NPS will eventually implement test-slaughter or contraception to eradicate brucellosis in bison.
Implementation of test-and-slaughter at present would eliminate two-thirds of the bison population and result in major, adverse effects to population demographics, sustainability, genetics, and ecological processes.
Contraception is still experimental in bison and some tests resulted in permanent infertility. Thus, its use on free-ranging bison to decrease the prevalence of brucellosis is not appropriate at this time. Research by the U.S. Department of Agriculture Animal and Plant Health Inspection Service (APHIS) is ongoing.
Reinfection of bison by elk would likely occur in the future.
The NPS is currently spending $1.2 million per year to implement the Interagency Bison Management Plan, with little tolerance for untested bison outside of Yellowstone National Park in Montana.
The cost of implementing remote delivery vaccination was estimated at $300,000 per year, or about $9 million over 30 years, which would be a 20% increase over current expenditures.
Economic approaches could be used to evaluate whether additional investment in bison management to reduce the already low risk of outbreaks in cattle (primarily from elk) is economically justified. The socioeconomic benefits and costs of various brucellosis management approaches need to be estimated and compared with each other and to the costs of an occasional brucellosis outbreak (and the costs of developing an effective vaccine for domestic livestock) to determine the level of management that is socially acceptable and achievable at a reasonable cost.
In the 2000 IBMP decision, the NPS agreed to work with other agencies to maintain the population of Yellowstone bison near a guideline of 3,000 and evaluate whether to vaccinate free-ranging bison inside Yellowstone National Park for brucellosis using a remote delivery method that did not involve capture. There was no commitment in the 2000 IBMP to actually implement remote vaccination—only to evaluate the safety, efficacy, feasibility, and likely effectiveness of the idea. The 2000 IBMP did assume that improvements in vaccines, delivery technology, and diagnostics would occur in the near future. However, anticipated progress with vaccines, delivery methods, and diagnostics has not occurred and is not expected in the near future.