When 66 Canadian wolves were released into Yellowstone National Park and Idaho 15 years ago, it was a last-ditch effort to revive an iconic species that had been hunted to near-extinction across most of the United States.
To the delight of biologists and environmental activists, the wily, carnivorous wolves quickly formed up into packs, spreading throughout the northern Rocky Mountains and across the Snake River into Oregon. By the end of 2010, according to the US Fish & Wildlife Service, they numbered at least 1,651 in 244 packs and 111 breeding pairs.
In Yellowstone, according to biologists, that changed the behavior and numbers of wolves’ main prey: elk, which had become lazy with no one to keep them on the move. Elk numbers decreased, streams and rivers ran cooler and cleaner, benefiting fish populations as well.