Bison Impacts and Monitoring

Why monitor the bison?

The House Rock bison herd on the Kaibab Plateau that migrated onto the North Rim of Grand Canyon National Park has adapted to various habitats; grazing and wallowing in park meadows, stampeding through dense forests, and occasionally venturing along the rim of the canyon. Concerns of ecological impacts and effects to archeological sites have increased over the years as these bison have begun to congregate around natural water sources and change their migration behaviors to stay within park boundaries for longer periods throughout the year. Park researchers and collaborators have been monitoring the impacts of this herd on the natural and cultural resources of the North Rim and are establishing a feasible reduction plan.


What do the studies show?

Population Size and Migration:


Aerial surveys with collaborating agencies have shown that this herd is steadily increasing and is currently estimated at a size of 400-600 animals, which has the potential to grow to an estimated 1,200-1,500 individuals within the next 10 years. GPS tracking of individual bison has resulted in the conclusion that these animals have changed their migration patterns between House Rock Valley Wildlife Area (U.S. Forest Service property designated for bison management) and Grand Canyon National Park and they have not returned to House Rock Valley since 2009, staying almost entirely within park boundaries.

Two bison walking through a forest, near a spring. One of these animals wears a bright orange GPS collar.
Collared bison on the North Rim of Grand Canyon National Park, 2017. (NPS camera trap photo)

Bison Behavior:


Camera traps deployed at North Rim water sources have documented the physical disturbance of natural resources and have been utilized to map out bison density on the North Rim to better understand interactions with other wildlife species. Determent of bison by fencing around favored water sources has proven unsuccessful.

A bobcat crouches and watches bison at a muddied water source in a grassy meadow.
Wildlife interaction at a disturbed water source on the North Rim of Grand Canyon National Park, 2017. (NPS camera trap photo)
A herd of thirty bison lay in wallows and trample through spring that has been fenced.
A herd of bison using a fenced off water source on the North Rim of Grand Canyon National Park, 2017. (NPS camera trap photo)

Impacts on Vegetation:

Vegetation research conducted around the water sources on the North Rim shows that as bison activity increases, soil disruption also increases. Soil disruption is not only a catalyst for the introduction of exotic species, but it has hindered the growth in height, abundance, and diversity of native plant species.

A large bison wallow at the edge of a forest is littered with invasive plants.
Invasive mullein growing in the disturbed soil of a bison wallow in Grand Canyon National Park, 2015. (NPS photo)

Effected Water Quality:

The drinking water in Grand Canyon National Park comes from Roaring Springs, fed by rain and snowmelt on the North Rim. Monitoring has indicated increased levels of E. coli bacteria in standing water associated with bison grazing areas. Large ungulate herds are known to cause significant damage to water sources through contamination and soil compaction. Park experts suggest that the ongoing damage inpacts to water quality by the House Rock bison herd on the Kaibab Plateau may be far worse than current research shows.

A herd of thirty bison stand in water source. The edge of the water is muddied and compact while the surrounding grass is trampled and littered with bison feces.
Soil compaction and water contamination by bison herd on the North Rim of Grand Canyon National Park, 2017. (NPS camera trap photo)

Threats to Archeological Sites:

Park archeologists have found significant threats to culturally rich areas of the North Rim from the ongoing impacts of the House Rock bison herd on the Kaibab Plateau. Research shows that these bison follow migratory patterns in search of water and resources. In doing so, the herds trample through archeological sites causing damage to artifacts and cultural features found on the surface and buried underground. This is apparent in the wallows and bison trails surrounding and within survey sites.

Large wallows and deep game trail in grassy meadow near forest's edge.
Large wallows and deep game trail in meadows on the North Rim, 2012.

In the next three to five years, the National Park Service will reduce the size of the House Rock bison herd on the Kaibab Plateau through capture and relocation, and lethal culling. The Environmental Assessment, Finding of No Significant Impact and other documents can be found on the NPS Planning Environment and Public Comment (PEPC) website.

Operational details of herd reduction are being worked out and more information, including volunteer opportunities, will be announced at a later date through a news release. This website
www.nps.gov/grca is the best source of up-to-date information. If, after browsing the information below, you are unable to find the answers to your questions email them to us at: e-mail us.

Related information:

Prepared by Desiree Espericueta, Wildlife Technician, Grand Canyon National Park (February 2018).