IBMP SUBCOMMITTEE ON ADAPTIVE MANAGEMENT OF BISON ABUNDANCE
Julie Cunningham (MFWP), Steph Gillan (CSKT), Karen Loveless (MFWP), Jim Stone (ITBC), Rick
Wallen (NPS), P.J. White (NPS), and Marty Zaluski (MDOL)
Assignment: Develop ideas for maintaining Yellowstone bison numbers near a target of 3,000.
Need: Large migrations by bison into Montana have resulted in occasional culls of 1,000+ bison when
attempts to deter these mass movements failed and there were concerns about brucellosis transmission to
cattle. Thus, managers want to implement more frequent, smaller, selective culls of Yellowstone bison to
dampen population growth and avoid possible unintended demographic and genetic effects of larger culls.
Issues and Concerns Raised by IBMP Managers (December 2010):
 Biggest issue is how to avoid large trap and slaughter events.
 What methods can we use to control population? How can we best understand when we are
approaching need for population control and “get ahead of the curve” so as to avoid major ship and
slaughter events?
 Who decides and what are the decision criteria for when to start and stop ship and slaughter
operations?
 Recognize that all of these issues are linked and also that we must move on all fronts at once if we are
to meet the twin mandates of the IBMP.
 For hunting we must look at available habitat, landowner tolerance, and risk of disease transmission.
 Need to continue modeling efforts to better understand movement as a function of bison population,
snow pack, and other drivers.
 Expand hazing and hunting opportunities. Hunting could be expanded from 44 to 144 animals. Tribes
could consider more intense hunting on the west side of the Yellowstone.
Desired Population Conditions:
 Bison abundance averages 3,000- 3,500, while maintaining 90-95% of existing genetic diversity over
the next 100 years.
 Sex ratio of about 50% males and 50% females. Age structure of about 70% adults, 10% yearlings,
and 20% calves.
 Approximately equal abundance in the central and northern breeding herds (Note: IBMP managers
could benefit from a presentation on the genetic differences and interchange between the central and
northern breeding herds, and discuss a minimum threshold to preserve genetic diversity).
 Maintain the processes of migration and dispersal.
 More than 50% decrease in brucellosis prevalence in bison
Population Modeling: NPS staff collaborated with Dr. Tom Hobbs at Colorado State University to
develop a model to guide adaptive management of the Yellowstone bison population by assimilating data
from ongoing population monitoring and designed studies of population processes. Simulations suggest
the annual removal of 200-300 bison from various age, sex, and herd classes will likely maintain the
population below 3,500 animals five years into the future. Culling could initially be focused on
seropositive females at capture facilities to help reduce the proportion of infectious bison (see below). As
brucellosis prevalence decreases, seronegative bison from various age, sex, and herd classes may need to
be culled to meet distribution and demographic goals.
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Possible Methods to Limit Abundance (see Table 1 for summary):
 Selective culling to (1) reduce the proportion of infectious bison, or (2) limit abundance based on
other distribution and demographic goals (age, herd, sex).
o Initiate selective removals of bison with a specified probability of being actively infected based
on age and quantitative serologic tests.
 FPA values are generally higher in seropositive bison that are culture positive compared to
seropositive bison that are culture negative, supporting that active infection is associated with
increased antibody production.
 Testing at capture facilities could allow for removing bison that most likely contribute to
brucellosis maintenance in the population, while keeping bison that contribute to herd
immunity which reduces brucellosis transmission.

Public and treaty harvests
o Expand hunting opportunities by increasing tolerance for bison on cattle-free public lands and
private lands with willing landowners, including year-round use in some areas.
o Additional tolerance with larger conservation areas for bison in Montana and non-traditional
harvest seasons (e.g., bulls during late winter) may be necessary to effectively use public and
treaty hunting to limit bison distribution and abundance because most bison do not migrate
outside the park until after mid-February. Otherwise, few bison will be harvested in many years.
o Coordinate bison vaccination and hunting seasons to allow a sufficient withdrawal time following
vaccination before bison may be harvested and consumed.

Transfer of bison to American Indian tribes or other conservation organizations
o Establish one or more quarantine facilities for test-negative calf and yearling bison on tribal lands
and transfer “surplus” Yellowstone bison to these facilities.
o Ship surplus untested and test-positive bison to slaughter facilities on tribal lands (e.g., Fort
Belknap)
o May need to conduct additional NEPA compliance.

Transfer bison to research facilities
o Quarantine facilities in Corwin Springs (e.g., APHIS contraception study)
o Remote vaccination research on vaccine efficacy and safety of biobullets, behavioral responses of
bison, etc.
o Diagnostics (PCR)
o Agricultural Research Service (remote vaccination, strain 82, etc.)

Contraception
o NPS staff collaborated with Dr. Paul Cross, U.S. Geological Survey, and Mike Ebinger, Montana
State University, to use an individually-based epidemiological model to assess the relative
efficacies of three management interventions (sterilization, vaccination, and test-and-remove).
Simulations suggested that sterilization of 50-100 young seropositive females per year could
achieve a large reduction in brucellosis seroprevalence, while simultaneously limiting population
growth. However, the field effort required to find the small segment of the population that is
infectious rather than susceptible or recovered may limit the utility of this approach.
o APHIS developed a research proposal to evaluate the effectiveness of a contraceptive vaccine to
reduce shedding of Brucella bacteria during the time period that a bison is actively infected with
brucellosis. The project will be conducted at leased facilities in the Gardiner basin (outside
Yellowstone National Park) using 80-100 bison of both seronegative and seropositive brucellosis
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o
o
status. The NPS issued a research permit on May 13, 2011 to transfer bison for the project to
APHIS.
Will need to comply with the Animal Medicinal Drug Use Clarification Act and complete an
Environmental Impact Statement since birth control and sterilization of bison were rejected from
in depth analysis in the Final Environmental Impact Statement for the IBMP (pages 59-60).
Representatives from Montana Fish, Wildlife, and Parks and the Confederated Salish and
Kootenai Tribes indicated they do not support the use of this technique on bison.
Natural mortalities (predation, winter-kill, etc.): Need better estimates of survival rates for various age
and sex classes in each breeding herd across a range of environmental conditions.
Management plan and coordination meetings: The NPS is developing an integrated management plan and
updated operations plan for review and comments by the other IBMP agencies. A possible approach is as
follows:
1. Conduct count/classification and complete management plan by end of July.
2. Establish annual culling objectives based on disease, distribution, and demographic goals (using
population and migration model).
3. Estimate range of possible winter-kill and predation losses, and numbers of bison migrating to park
boundaries, based on weather predictions, predator densities, etc.
4. Attend meeting in late July or August with MFWP and treaty tribes to discuss harvests.
5. Update operations plan with possible management actions for the coming winter.
6. As planned, implement disease suppression culls of likely infectious bison and vaccination of eligible
bison at Stephens Creek and Duck Creek capture facilities.
7. As planned, transfer bison to slaughter facilities and/or quarantine on tribal lands.
8. As planned, transfer bison to research projects.
9. Estimate actual hunter harvest, winter-kill, predation off-take, and management culls.
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Table 1. Evaluation of possible management actions to limit bison abundance based on acceptance, compliance, cost, and success criteria.
Management Action
Success in limiting bison
numbers
Cost
Public acceptance
Level of compliance
Selective Culling at
Capture Facilities
Depends on the extent of
migration
High
Low
Evaluated in FEIS for
IMBP
Public and Treaty
Harvests
Variable, but <200 bison
harvested per season to date
Low
Generally high
Public harvests
addressed in FIES for
IBMP and MEPA;
Treaty rights
recognized by Montana
Transfer Bison to
Tribes
Little long-term effect
High initially
(infrastructure)
Variable: strong
resistance in some
sectors and adjacent
livestock owners
USDI Secretary has
authority; May need
additional NEPA
Transfer Bison to
Research Facilities
Little effect based on the
capacity of research facilities
Low
Variable: typically
more palatable than
slaughter
USDI Secretary has
authority and evaluated
in FEIS for IMBP
Contraception or
Sterilization
Depends on the extent of
implementation. Could
feasibly have large effect if
broadly implemented or
when combined with
vaccination of other bison
Low following
initial research
and deployment
costs
Variable: low in
some sectors, but
more palatable than
slaughter
Will need NEPA
because not evaluated
in FEIS for IBMP
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Comments
Provides
opportunity for
prevalence
reduction activities
Addresses
population growth
and transmission