TRAVERSE CITY, Mich. (AP) — Gray wolves are thriving at Isle Royale National Park five years after they nearly died out. Authorities airlifted 19 mainland wolves to Lake Superior park to rebuild a population that had fallen to just two, mostly because of inbreeding. A report Wednesday by Michigan Technological University scientists says the population has reached 31. Wolves continue preying on moose, but moose are still overpopulated and struggling to find food. Some argue against human intervention in wilderness areas such as Isle Royale. But others say a good balance of wolves and moose are needed there to keep the forest healthy.