Stay clear of bull bison like this fellow in Pelican Valley (Trail 23)

      Estimates of the numbers of the seven species of native ungulates vary as widely as the large animals’ migratory range. Counts of Yellowstone’s bugling Rocky Mountain elk (also known as wapiti) vary seasonally from 10,000 to 20,000 in summer to 5,000 in winter, in seven distinct herds. Over 100,000 elk inhabit Greater Yellowstone. In summer, you can hardly toss a bison chip without hitting a member of the largest elk herd in North America: look around Gibbon Meadows or the Lamar Valley. During the autumn rut (mating season), elk take over the lawns around Mammoth Hot Springs and flock to meadows around Norris Geyser Basin. In Jackson Hole, Timbered Island becomes a no-go zone during the rut. In winter, they migrate south to the National Elk Refuge, or north and east to Gardiner and West Yellowstone, where hunters await just beyond the park boundaries.

      Yellowstone’s population of persistent bison (often used interchangeably with buffalo), the largest land animal in North America, is estimated at between 2,300 and 5,000. Watch year-round for what remains of the United States’ largest free-roaming herd in the Hayden and Lamar Valleys, in summer in open meadows and grasslands, and in winter in thermal areas and along the Madison River. In Grand Teton, smaller herds roam the sagelands around Mormon Row. In 2016, President Obama signed legislation designating the bison as the national mammal of the United States.

      Common, floppy-eared mule deer prefer open forests and grassy meadows, where they munch on leaves, shrubs, and sedges. Watch for them browsing around dusk near forest edges. The furtive, less common white-tailed deer is only occasionally spotted near waterways in Yellowstone’s Northern Range.

      A declining population of moody, drooling moose lurk in willow thickets in riparian zones, mainly in marshy meadows, near lakeshores, and along rivers. In Yellowstone, they are most frequently seen browsing in the Bechler region and in the Soda Butte Creek, Pelican Creek, Lewis River, and Gallatin River drainages. They are more common in Grand Teton, wherever willows colonize marshes and ponds. Appearances are deceptive: they are superb swimmers and can—and will—charge at up to 35 miles per hour, so give them wide berth.

      A population of 350–400 fleet-footed pronghorn are more closely related to goats and are not true antelopes. They are found in summer in sage flats and grasslands in the Lamar Valley, in Jackson Hole, and near Yellowstone’s North Entrance. Their numbers declined by 50% in Yellowstone between 1991 and 1995; for context, the pre-European American settlement population is estimated at 35 million. The population has since stabilized, but large-scale energy developments outside Grand Teton jeopardize their long-distance winter migration routes around the park.

      Numbering up to 300, Rocky Mountain bighorn sheep are often spotted scampering along cliffs and roaming Yellowstone’s alpine meadows. In summer, they are most easily found on the slopes of Mount Washburn, and yearround in Gardner Canyon between Mammoth and the North Entrance. Also watch for their silhouettes on cliff tops along the Yellowstone River, and above Soda Butte in the Lamar Valley.

      Invasive, nonnative mountain goats are increasingly common and thought to be colonizing rocky slopes in Yellowstone’s northern reaches.

      The population of the seldom-seen American cougar (also known as the mountain lion) is estimated at 26–42, making it Yellowstone’s most common cat species. Primarily nocturnal, cougars have been called “the ghosts of the Rockies.”

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