is no simple carrying capacity figure for any wildlife species,
and the number is in constant flux. The truth is, we need
to think outside the box; Yellowstone National Park is drawn
like a box, and it neither reflects the ecosystem nor the
needs of the creatures that are part of that ecosystem.
The tremendous influence natural variations have on sustainable
population levels must be taken into account when contemplating
carrying capacity. Weather patterns such as wet seasons,
times of drought, harsh winters or milder winters impact
populations. Predator-prey relationships also alter the
picture. Carrying capacity is wrongly being considered only
for the Park, within a political boundary invisible to wildlife,
rather than being extended to adjacent public lands (i.e.
Gallatin National Forest) from which buffalo are systematically
A figure of 3,000 buffalo, cited in the Interagency Bison
Management Plan, is frequently touted as a carrying capacity.
It is not. Rather than being based on available habitat
or sound science, this figure is politically derived.
A National Academy of Sciences study conducted in 1998 determined
that “even at 3,500 bison, little or no evidence exists
to indicate that forage quantity or quality is inadequate.”
The report goes on to say that even if the buffalo population
has enough forage to maintain itself above 3,000 animals,
natural weather factors that prevent buffalo from accessing
that forage, such as deep snow, will cause them to migrate
to lower elevations, and out of the Park.
The 3,000 buffalo constraint is simply being used to make
it more convenient for buffalo to be managed, at the expense
of the wild nature and genetic integrity of America’s
last wild and unfenced herd. Further, the Park Service has
a clear statutory mandate for noninterventionist wildlife
management. In other words, natural factors are intended
to regulate the size, distribution, movement patterns, and
habitat use patterns of wildlife within our parks.
What is known for certain is that, due to yearly killing, over 3,500 buffalo have been slaughtered in the ten years since the Interagency Bison Management Plan has been in effect. When buffalo migrate beyond the Park and enter Montana, Department of Livestock officials take charge. Instead of wildlife biologists, brand inspectors control wild buffalo, and biologists don't have a chance to evaluate restoring natural populations in the ecosystem.
The overpopulation argument is made for buffalo, elk, and other ungulates. The park is said to be overgrazed, yet for at least the past century, there's arguably been no better place in the United States to witness wildlife than Yellowstone National Park. It is now, and for decades has been, America's wildlife Serengeti. The notion that the Park is overpopulated and the buffalo population unsustainable is simply not true.
Montana has a grand opportunity that would be the envy of
the entire country; Instead of driving a policy to kill
America’s last wild buffalo for reasons that have
little to do with disease or population control, Montana
could be the only state to boast a truly wild, free-roaming
herd of buffalo. Buffalo are the icon of the West, and Montana
should consider celebrating them as its national mammal.
Montana can end the buffalo slaughter that began in the
19th century once and for all. Montana has the wisdom and
national support to make it happen.
(See our Overpopulation
Fact Sheet for more info)
Plumb et al, Carrying capacity, migration, and dispersal in Yellowstone bison.
May 2009- While this paper places too much emphasis on so-called social and political factors in limiting the abundance and distribution of the population, it does take a hard look at the capacity of Yellowstone National Park alone to sustain wild buffalo. Their scientific modeling suggests buffalo "have not reached a theoretical food-limited carrying capacity of 6200 in Yellowstone National Park." (PDF- 11 pages, 782 kb)
Taper et al, The Phenology of Space: Spatial Aspects of Bison Density Dependence in Yellowstone National Park.
October 2000- This paper capitalizes on a unique opportunity provided by the record of the bison population inhabiting Yellowstone National Park and the Yellowstone ecosystem. This population has been intensely monitored for almost four decades. There does not appear to be another comparable data set in existence for a very large highly gregarious herbivore (G. Caughley pers. comm. to MM). The Yellowstone population has a long historical record with some information dating back to 1860 (Meagher 1970, 1973). Further, these wild bison herds have been the subject of long-term detailed and continuous ecological study since 1963. (PDF- 113 pages, 2.6 MB)