Survival, always the top priority of wildlife, becomes even more critical as fall signals the approaching winter. As home to the largest concentration of mammals in the lower 48 states, and an area where the human impact on wildlife is relatively limited, Yellowstone National Park is a setting where winter is a true test of survival. While there are 61 separate species of mammals in Yellowstone, those falling into the “Prey/Predator” category have become “marquee” attractions.
Best-equipped to handle winter are Yellowstone bears. During the fall and early winter, black and grizzly bears spend most of their time feeding in order to store enough calories to hibernate. This pre-denning period is known as “hyperphagia.” Visitors to Yellowstone can see bears until they enter their winter dens between mid-October and early December. An estimated 500-650 black bears and 280-610 grizzly bears live in the park.
Yellowstone Bison (Buffalo)
Bison have long been recognized as a symbol of the American West, and their presence in Yellowstone offers an interesting history. While bison in the United States once numbered close to 70 million, by the early 1900s they were close to extinction. In 1902, the Yellowstone herd was down to about two dozen when a campaign to restore the animal to the park began.
By protecting the herd and supplementing it with bison from other parts of the country, the U.S. Army – and later the National Park Service – was able to allow the animal to repopulate to the point where some 4,000 of the animal reside in Yellowstone today. Bison are found throughout the park and are easily viewed year-round.
Yellowstone Elk are the most abundant large mammal found in the Park with their numbers ranging from 15,000 to 25,000 in summer and 8,000 to 20,000 in winter. The herd on the northern range in Yellowstone is one the two largest in the country. Fall is the best time to view elk as the bulls sport full racks of antlers and the rutting season runs from early September to mid-October. During that time, bulls bugle and fight to announce their fitness and availability to females.
Elk tend to move to higher elevations during the summer and return to lower elevations in the fall as certain grasses offer maximum nutritional levels that last roughly two weeks. The return of wolves to the Greater Yellowstone Ecosystem has resulted in the reduction of the herd size as older and sick elk are killed by the wolves.
Since wolves were reintroduced in the park in 1995 and 1996, they have become the most discussed and controversial animal in Yellowstone. With approximately 175 wolves residing in the park, they are spotted on a daily basis, particularly in the Lamar Valley.
Elk are wolves’ primary source of food. Because they posses a large paw that allows them to run on top of the snow without sinking deeply, wolves are well-suited for winter when elk tend to sink into the snow and are less able to run away from the wolves. Elk also exhibit a low energy level during the winter. Wolves that tend to follow the elk herds are easier to spot as fall arrives.
Yellowstone Mountain Lion (Cougar)
Extremely difficult to spot in the park, the cougar – also known as the mountain lion – is the largest member of the cat family in North America. Some 15-17 cougars live in Yellowstone, but they are also follow the elk herds and move to lower elevations in winter.
Yellowstone National Park is also home to a wide variety of other mammals such as fox, coyote, bighorn sheep, otter and more.
Visitors to the park who wish to spend several days observing Yellowstone wildlife and learning about the park with local experts have many choices, including two Yellowstone Lodging and Learning programs offered by Xanterra Parks & Resorts and the non-profit Yellowstone Association Institute. Instructors, such as professional naturalists, scientists and artists, lead the programs. All instructors have abundant experience in Yellowstone, and most have advanced academic degrees in their fields. A great many of the instructors have authored books on their subjects.