Yellowstone National Park
There are over 30,000 elk; this is the largest number of any big mammal species in Yellowstone. The northern herd has become much smaller since the mid-1990s. Wolves may cause this. Also, elk use more forested areas to hide from the wolves. This makes it harder for researchers to count them. The northern herd migrates west into southwestern Montana in the winter. The southern herd migrates south, and most of these elk stay on the National Elk Refuge during winter, southeast of Grand Teton National Park. The southern herd migration is the biggest migration of mammals in the U.S. outside of Alaska.