 Bison
are the largest mammals in Yellowstone National Park.
They are strictly vegetarian, a grazer of grasslands and
sedges in the meadows, the foothills, and even the
high-elevation, forested plateaus of Yellowstone. Bison
males, called bulls, can weigh upwards of 1,800 pounds.
Females (cows) average about 1,000 pounds. Both stand
approximately six feet tall at the shoulder, and can
move with surprising speed to defend their young or when
approached too closely by people. Bison breed from
mid-July to mid-August, and bear one calf in April and
May. Some wolf predation of bison is documented in
Canada and has recently been observed in Yellowstone.
Yellowstone is the only place in the lower 48 states
where a population of wild bison has persisted since
prehistoric times, although fewer than 50 native bison
remained here in 1902. Fearing extinction, the park
imported 21 bison from two privately-owned herds, as
foundation stock for a bison ranching project that
spanned 50 years at the Buffalo Ranch in Yellowstone's
Lamar Valley. Activities there included irrigation,
hay-feeding, roundups, culling, and predator control, to
artificially ensure herd survival. By the 1920s, some
intermingling of the introduced and wild bison had
begun. With protection from poaching, the native and
transplanted populations increased. In 1936, bison were
transplanted to historic habitats in the Firehole River
and Hayden Valley. In 1954, the entire population
numbered 1,477. Bison were trapped and herds
periodically reduced until 1967, when only 397 bison
were counted park wide. All bison herd reduction
activities were phased out after 1966, again allowing
natural ecological processes to determine bison numbers
and distribution. Although winterkill takes a toll, by
1996 bison numbers had increased to about 3,500.
Bison are nomadic grazers, wandering high on
Yellowstone’s grassy plateaus in summer. Despite their
slow gait, bison are surprisingly fast for animals that
weigh more than half a ton. In winter, they use their
large heads like a plow to push aside snow and find
winter food. In the park interior where snows are deep,
they winter in thermally influenced areas and around the
geyser basins. Bison also move to winter range in the
northern part of Yellowstone.
 Bison
are enjoyed by visitors, celebrated by conservationists,
and revered by Native Americans. Why are they a
management challenge? One reason is that about half of
Yellowstone's bison have been exposed to brucellosis, a
bacterial disease that came to this continent with
European cattle and may cause cattle to abort their
first pregnancy after exposure to Brucella bacteria. The
disease has few population level effects. Outside the
park wild bison from the Yellowstone population have not
been known to transmit brucellosis to a visitor or to
domestic livestock. The State of Montana believes its
"brucellosis-free" status may be jeopardized if bison
commingle with cattle. The risk of Yellowstone bison
transmitting brucellosis to nearby livestock is very
low. However, if livestock are infected, ranchers can be
prevented from shipping livestock out of state until
stringent testing and quarantine requirements are met.
Some elk in the Greater Yellowstone ecosystem also carry
the disease.
Most Yellowstone wildlife move freely across
administrative boundaries set a century ago. Bison
however, are not always welcome outside the park.
Managers have tried to limit bison use of lands outside
the park through public hunting, hazing bison back
inside park boundaries, capture, testing for exposure to
brucellosis, and shipping them to slaughter.
The NPS, U.S.D.A. Forest Service, U.S.D.A. Animal and
Plant Health Inspection Service, and the State of
Montana completed an Environmental Impact Statement for
the Interagency Bison Management Plan for the State of
Montana and Yellowstone National Park in November 2000.
Alternatives considered ranged from: allowing bison to
freely range over a large portion of public land inside
and outside the park; managing bison like elk and other
wildlife through controlled hunting outside park
boundaries; and attempting to eradicate brucellosis by
capturing, testing, and slaughtering infected bison at
numerous facilities constructed inside the park.
Additional options included purchase of additional
winter range; attacking brucellosis with a safe and
effective vaccine for bison; and quarantine of animals
at appropriate locations such as Indian Reservations or
other suitable sites outside Yellowstone.
State and Federal Records of Decision were signed in
December 2000. The purpose of the IBMP is to maintain a
wild free-ranging bison population and to address the
risk of brucellosis transmissions to protect the
economic interest and viability of the livestock
industry in Montana. The principles of the Interagency
Bison Management Plan include the following concepts:
- The State of Montana is responsible for managing
bison when they leave the park and is the lead
agency when conducting capture operations in the
western Special Management Area
- National Park Service is responsible for all
actions conducted within the park and is responsible
(currently) for keeping bison from leaving the park
in the area of Reese Creek along the northern
Special Management Area
- Abundance and distribution of bison are
monitored throughout the year
- When bison move beyond an established tolerance
area the following procedures are implemented to
enforce spatial and temporal separation between
bison and cattle:
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- All cattle within and near special management
zones adjacent to YNP are vaccinated
- Vaccinate eligible bison (initially calf and
yearling animals)
- An Adaptive Management strategy is incorporated
for systematically increasing tolerance of bison on
low elevation winter range outside of Yellowstone
National Park:
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Steps towards
greater tolerance
for bison outside Park
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Steps toward a fully implemented
bison
vaccination program
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| Step 1. Minimum tolerance
outside Park; up to 100 bison allowed outside of
park if test negative |
Step 1. Vaccinate bison at
capture pens |
| Step 2. Moderate
flexibility to tolerate bison outside park (at
the discretion of the Montana State
Veterinarian); remote vaccination of eligible
bison outside Yellowstone NP may be implemented
in place of capture |
Step 2. Remotely vaccinate
bison in Zone 2 of Special Management Areas when
the State of Montana chooses to tolerate
untested bison outside park and hand vaccinate
bison at capture pens |
| Step 3. Maximum tolerance;
up to 100 bison allowed outside of the park
(untested) |
Step 3. Remotely vaccinate
bison in both the Special Management Areas and
inside Yellowstone National park as well as hand
vaccination of bison at capture pens |
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