Yellowstone Bison (IMAGE) University of Wyoming Caption Bison graze on a patch of green grass in late summer in this August 2016 photo from Yellowstone National Park's Lamar Valley. Researchers have found that intensive grazing and fertilization by bison allow them to reset the clock on springtime plant growth, so they can migrate on their own terms, unlike mule deer and other ungulates. Credit Neal Herbert, National Park Service Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.