This month-old calf is a member of the Porcupine caribou herd, a group in the Yukon with rising population growth at a time when others are experiencing dangerous declines. Its success might now be threatened. The herd’s birthing grounds in Alaska were recently opened up for industrial development by the U.S. government. That’s bad news, says photographer Peter Mather, who witnessed the resilience of the animals first-hand. “When they were born they were tiny, skinny caribou and could hardly walk, and a month and a half later they’re travelling hundreds of kilometres.” This photo was captured by a remotely controlled camera in the Richardson Mountains. The Porcupine herd nearly doubled in size over 15 years, growing to as many as 235,000 animals in 2017. Mike Suitor, a Yukon government biologist, says the exact reasons for its success are unknown, but the herd’s largely protected and varied habitat—spanning Alaska, the Yukon and parts of the N.W.T.— is a factor. The Porcupine Caribou Management Board deserves credit, too. Made up of representatives from Indigenous groups and Canadian government officials, it monitors herd numbers and regulates hunting.