February 12, 1995

Snowmobiling Boosts Bison

Associated Press

Snowmobile trails in Yellowstone National Park have helped the park’s bison population almost double, according to National Biological Survey studies.

Park ranger Norm Bishop, citing studies by NBS biologist Mary Meagher, said the herd now numbers about 4,300 animals, an increase of about 2,000 from past years attributed to the presence of the groomed snowmobile trails.

Bishop said the trails allow bison to move around the park in search of food and even leave the park if food sources become scarce or covered with snow.

“Instead of being trapped by deep snow and limited to food sources in a particular area, the bison can move around and expend less energy doing it,” he said. “It basically improves their ability to survive the winter.”

Stu Coleman, chief of the park’s Natural Resources Center, said the herd’s growth will probably continue, but he added it will be difficult to predict how fast the herd will grow.

“A lot will depend on the harshness of the winters,” he said.

Coleman said that based on the park’s theory of natural population regulation, the bison herd should reach a point at which it can no longer be sustained and then numbers will start to drop.

He added the number of bison moving out of the park will probably increase as the herd does.

The herd’s growth has caused some concern about potential overgrazing and other habitat damage, but Coleman said Meagher’s studies showed that the park is not experiencing. However, the studies did show an increase in “mechanical impacts” such as the number of wallows and trails and the amount of tree-rubbing in the park.

Coleman said studies also have not revealed any losses of certain native plants, an indicator of overgrazing.

The herd’s expansion shows that the park has not reached its carrying capacity for bison, Coleman said, although he added no one is sure what the capacity is.

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