In 2015, the familiar cacophony of Alaska’s common murre colonies fell eerily quiet. When summer field crews arrived at their monitoring sites, they found only a scattering of common murres on cliffs where thousands of birds should have been.

Yellowstone National Park’s winter season begins Sunday, Dec. 15. Annually from mid-December until mid-March, visitors can travel most of the park’s roads from the West, South, East and North entrances by approved commercially guided snowmobiles and snowcoaches and via the non-commercially guided snowmobile access program.