On a hazy July afternoon, wolf expert Karin Vardaman returned to a spring-fed pond in Colorado’s northwestern-most corner. Enough rain had fallen to wet the ground around the watering hole. She tiptoed across the soft earth — careful not to disturb any impressions left by cattle and pronghorn antelope — until one track filled her with an almost overwhelming feeling of relief. There, sunken into the mud near the Wyoming and Utah borders, was a broad wolf print. “Maybe there’s one,” she said. “It gives hope.” For nearly two years, Vardaman has visited the Moffat County rangeland every few months to track wolves for Working Circle, a nonprofit she founded...