In this August 3, 2016 photo, a large bison blocks traffic in the Lamar Valley of Yellowstone National Park as tourists take photos of the animal. Record visitor numbers at the nation's first national park have transformed its annual summer rush into a sometimes dangerous frenzy, with selfie-taking tourists routinely breaking park rules and getting too close to Yellowstone's storied elk herds, grizzly bears, wolves and bison. (Photo by Matthew Brown/AP Photo)
