The easiest animal to spot in Yellowstone, is also the largest. Bison males (bull) weigh up to 2,000 pounds, females (cow) weigh up to 1,000 pounds. Males tend to be larger than females and have a larger, wider head. Males and females both have horns. The population is estimated at 4,900 as of July 2015. Bison may live 12–15 years, a few live as long as 20 years. They feed primarily on grasses and sedges.
Bison mate (the rut) in late July through August which is a great time to visit and observe the posturing, grunting and fighting of the male bison. Females give birth to one calf in late April or May. In spring, you will notice that the larger groups are nursery herds: comprised primarily of females and their young. Like many ungulates, males form small bachelor groups or go off on their own, leaving the cows to raise the young. The herd protects each other. They will circle around calves to prevent attacks from predators. Primary predator threats are grizzly bears and wolves. Calves are especially vulnerable.
Where to See Bison:
- Bison can be spotted throughout the park.
- Year-round: Hayden and Lamar valleys.
- Summer: grasslands.
- Winter: geothermal areas and along the Madison River. Blacktail ponds, Mammoth and Tower areas.
Outside of Yellowstone, I have observed Bison in Theodore Roosevelt National Park, North Dakota; Custer State Park, South Dakota; National Bison Range; Montana; Soapstone Prairie, Northern Colorado; and Rocky Mountain Arsenal National Wildlife Refuge near Denver, Colorado.
Bison litter the hillside in Lamar Valley of Yellowstone
Bison are fairly easy to photograph because they can be found along roadways. They also will stay in one area for extended periods of time which makes them a good model for beginners. They are still a wild animal and have been known to charge when upset. Yellowstone National Park requires you to stay 25 yards away from Bison. One clue that a bison is upset is a raised tail.
A female bison and calves
Nursery herd of bison (females & calves) feeding on the grasslands of Yellowstone
Bison grazing in the Biscuit Basin geothermal area
During the rut, male bison pee into wallows (the area under this male) and then role in it as part of the courtship ritual
A mother bison with her calf
Crossing the Lamar River, bison are good swimmers
In the winter, bison use their strong necks and large heads, sweeping back and forth to clear snow from plants. They migrate out of the highest elevations of the park and some migrate outside of the park.
Bison follow each other through snow to save energy, they are observed to take turns leading
An area where the bison have been moving snow around with their heads to find grasses
The frost on the outer fur of this bison is a sign that the insulating layer is working well
