Being Caribou: Five Months on Foot with an Arctic Herd

For eons, female members of the Porcupine caribou herd have made the journey from their winter feeding grounds to their summer calving grounds—which happen to lie on vast reserves of oil. They once roamed borderless wilderness; now they trek from Canada, where they’re protected, to the United States, where they are not.

In April 2003, wildlife biologist Karsten Heuer and filmmaker Leanne Allison set out with the Porcupine caribou herd. Walking along with the animals over four mountain ranges...