Fiona Rogers / Japanese Macaque (Macaca fuscata) baby in a geothermal spring, Jigokudani Monkey Park, Japan

Fiona Rogers / Japanese Macaque (Macaca fuscata) baby sucking its toe in a geothermal spring, Jigokudani Monkey Park, Japan

Kirkendall-Spring / Travertine limestone terraces of Mammoth Hot Springs in Yellowstone National Park, Wyoming, USA, June 2013.

Diane McAllister / Japanese Macaque (Macaca fuscata) adult with wet snowy head in the hot springs of Jigokudani, Japan.

Diane McAllister / Japanese Macaque (Macaca fuscata) adult in the hot springs of Jigokudani, in the snow, Japan. February

Ben Cranke,Ben Cranke / Japanese Macaques (Macaca fuscatata) grooming in hot springs, Jigokudani, Nagano Prefecture, Honshu, Japan

Diane McAllister,Diane McAllister / Japanese Macaque (Macaca fuscata) juvenile approaches the hot springs and feeding area covered in icy snow from the cold night before in Jigokudani, Japan, January

Diane McAllister,Diane McAllister / Japanese Macaque (Macaca fuscata) with icy strands of fur on its head, Jigokudani, Japan, February

Diane McAllister,Diane McAllister / Japanese Macaque (Macaca fuscata) females gather at one end of the hot springs, Jigokudani, Japan, February

Jeff Vanuga / Aerial view of Grand Prismatic Springs Midway Geyser Basin. Yellowstone National Park, Wyoming, July 2011.

Erlend Haarberg / Blahver hot spring and Eyvindarhver fumarole, Hveravellir, Iceland, May 2010

Charlie Summers / Mustang (Equus caballus) herd trotting in light snow covered prairie, IRAM Wild Horse Sanctuary south of Hot Springs, South Dakota, USA, May