Not at all, according to a study by a former Montana State
University graduate student who spent two winters documenting the
shaggy beasts' precise movements in the park's western section.
"Most of the travel is not taking place on groomed roads," said
Dan Bjornlie, who finished his master's degree in ecology at MSU
last spring. He currently works for the Wyoming Game and Fish
Department.
The project was instigated by the mass exodus and shooting of
bison during the 1996-97 winter, said Bob Garrott, an MSU ecology
professor and project advisor. Some suspected the bison were
exploiting the groomed roads to leave the park, a hypothesis
repeated so frequently by the media as to appear as fact, he
said.
"Dan's the first person to directly address that question with
field studies, and his intensive work does not support this
hypothesis," Garrott said.
The study, funded by the Biological Resources Division of the
U.S. Geological Survey, has been accepted for publication in the
Journal of Wildlife Management.
"There are people who believe that the groomed trails are making
those animals change their patterns, but with the research that's
being done...we just aren't seeing that," Yellowstone National
Park spokeswoman Marsha Karle told the Billings Gazette.
Bjornlie monitored bison in the Madison, Firehole and Gibbon
river drainages from November 1997 to May 1998 and from December
1998 to May 1999. In all, he and his team logged 28,293 bison
observations. Only 8 percent of the time were bison travelling.
Up to 20 percent of that travel time was on roads, but more often
the animals followed natural corridors, streambanks and packed
trails, Bjornlie found.
"The data show that of all activities, a really small part is
travelling, and of that, a small part is travel on the roads,"
Bjornlie said.
What's more, bison road use peaked in the months before and after
the roads were groomed, especially after mid-April when spring
thaws opened up new foraging areas.
"It's not even a fifty-fifty, on-road/off-road split. It's so
much lower than that," Bjornlie said. "The majority of movement
is off road."
The results challenge several assumptions about the ecological
role of groomed trails on bison survival and behavior. For
example, the study yielded no evidence that the animals use
groomed roads for travelling long distances. Most--68
percent--travelled less than 1 kilometer while on groomed
terrain.
"I've seen them walk from a streambed up to a road, walk 500 to
600 meters along the road, then go off into another streambed,"
Bjornlie said. "It's part of their travel. They definitely use
them [groomed roads], but they are part of a much larger travel
network that includes off-road travel."
The study instead documented heavy travel over the Mary Mountain
Trail linking the Hayden Valley, where many of the animals in the
study spend the summer, to the Firehole area, where the majority
of them winter. Using infrared monitoring stations, Bjornlie
recorded between 100 and 700 bison events in a two-week period
along the trail.
Visitors to the park more than 100 years ago told of bison
following the same trail, suggesting to Bjornlie that the nomadic
animals re-established the migration pattern once their numbers
began rebounding. When population control efforts ceased in 1967,
there were about 400 bison in the park. Before the big die-off in
1996-97, there were about 3,500.
"So they're moving because of range expansion, not because of the
roads," Bjornlie said.
Park spokeswoman Cheryl Matthews said data collection on bison
movement in the park will continue. Because the park hasn't yet
experienced another winter as harsh as the 1996-97 one, when so
many bison left the park and were shot, data from another tough
winter will be critical to see if the trend of not using roads
continues, she said.
