Earlier this month Yellowstone National Park opened its roads to oversnow vehicles for the winter season and suspended a wildlife monitoring program that found snowmobiles and other such machines were having minimal effects on animals.
The monitoring program for wildlife along road corridors used by snowmobiles and larger, multi-passenger snow coaches began after Yellowstone adopted a plan in 2013 that restricted the number of winter vehicles allowed in the park.
The plan followed years of legal disputes and temporary restrictions on the types and number of vehicles allowed, fueled by concerns that too many snowmobiles were harming air quality and disrupting the park’s bison and other wildlife.
Wildlife workers observed more than 1,100 groups of animals over seven years with the restrictions in place.
They found that 95% of bison and 81% of trumpeter swans had either no response to nearby oversnow vehicles or a “look and resume” response, meaning the animals would look up and then resume what they had been doing.
The park also evaluated air quality and found that pollution levels dropped significantly after cleaner-burning snowmobiles were introduced in 2003.
While the monitoring program is suspended, rules governing winter vehicle use in the park remain unchanged.
Snowmobiles first appeared in Yellowstone in 1963, according to the park.
They became increasingly popular in the following decades as a way to access remote areas.
By the late 1990s, almost 800 snowmobiles daily on average entered the park during winter.
Under the rules put in place in 2013, the park requires winter visitors to travel in groups and allows up to 110 groups daily.
Guided snowcoach and snowmobile tours and up to four non-guided snowmobile groups daily are allowed, beginning typically in mid-December and continuing through mid-March.
However, travel this year is limited for now to snowcoaches only because of snow conditions, park officials said.