Yellowstone National Park is a sanctuary for the American bison, an iconic species. The park hosts the largest free-ranging bison population on public land, a conservation success story after their near extinction in the late 19th century. In 1902, the Yellowstone bison population dwindled to roughly two dozen. Through protection efforts, their numbers have rebounded, with estimates ranging from 3,500 to 6,000 in recent years. This population is unique, as it is the only place in the contiguous United States where bison have continuously lived since prehistoric times without reintroduction.
Bison Habitats and Movements
Bison in Yellowstone National Park utilize diverse habitats and exhibit seasonal movements. Key areas include the Lamar Valley, Hayden Valley, Pelican Valley, and the West and Central Plateaus. The Lamar Valley, often called the “Serengeti of North America,” and Hayden Valley are well-known for frequent bison sightings. These valleys offer grazing areas, especially during warmer months.
Seasonal changes trigger migrations for bison. Movement is influenced by snow depth and forage availability. As spring arrives, bison migrate to higher summer ranges, including the Mirror and Pitchstone Plateaus.
Distribution can also be affected by factors like rutting season and biting insect populations. For instance, herd groups may shift from Hayden Valley in July when biting insects are prevalent. The two primary breeding herds, northern and central, utilize parts of the park, though some intermixing occurs.
Managing Yellowstone’s Bison Population
Managing Yellowstone’s bison population is complex, involving multiple agencies. Goals include sustaining a free-ranging population while addressing brucellosis, population size, and migration beyond park boundaries. Brucellosis is a bacterial disease transmissible to cattle, and its presence in some Yellowstone bison has led to management challenges. Scientific advancements and changes in cattle operations near the park have reduced the perceived risk of transmission, with no cases directly linked to bison since 1998.
Collaboration among federal, state, and tribal agencies is key to this management. The Interagency Bison Management Plan (IBMP) guides efforts, aiming to separate bison and domestic livestock to prevent disease spread. The plan also considers the ecological role of bison within the park and the cultural significance to Native American tribes. Management strategies include hazing, public and tribal hunts, and the Bison Conservation Transfer Program, which relocates brucellosis-free bison to tribal lands.
Where and How to Observe Bison Safely
Yellowstone National Park offers opportunities to observe bison, particularly in well-known areas. Lamar Valley and Hayden Valley are recommended for high likelihood of bison sightings, especially during early morning and late evening. Bison are also seen near the Old Faithful area and Pelican Valley. Designated pullouts and parking areas along park roads provide safe viewing locations.
Observing bison requires adherence to safety guidelines. Visitors must maintain a minimum distance of 25 yards (23 meters) from bison. Bison, despite their calm appearance, are wild and unpredictable, capable of charging quickly and running up to three times faster than humans. It is illegal to approach wildlife to a degree that disturbs or displaces them.
Staying in vehicles when bison are on or near the road is advised. Using binoculars or telephoto lenses allows for safe viewing without getting too close. Never feed bison or other wildlife; this can lead to animals becoming aggressive and dependent on human food. Remaining on designated trails and avoiding meadows, particularly when bison are present, contributes to safety.
Bison’s Role in the Yellowstone Ecosystem
Bison are keystone species and ecosystem engineers within Yellowstone National Park, shaping the landscape. Their grazing patterns influence plant diversity and grassland structure. By consuming grasses, bison create a mosaic of grazed and ungrazed areas, stimulating new plant growth and allowing forbs to flourish. Selective grazing can extend the growing season for plants, making them more nutritious.
Wallowing behavior, where bison roll in dust or dirt, creates depressions that collect rainwater. These temporary wetlands provide habitat for insects and amphibians. Bison contribute to nutrient cycling through their urine and feces, returning elements like nitrogen, phosphorus, calcium, sulfur, and magnesium to the soil. Their presence and activities maintain the ecological balance and health of the Yellowstone ecosystem.