The following was posted online at YNP Wildlife today:
Bull bison are starting to make their way over Sylvan Pass into Yellowstone from the Shoshone National Forest. Please keep an eye out for them as they are often walking in the road and sometimes will even sleep in the middle of it. They are mostly heading to the Hayden and Pelican Valley areas. The bison rut starts in early August, and afterwards a large number of bulls will head back out again.