The largest North American mammal has only three predators: the grey wolf, the grizzly bear, and the human being. The First Nations hunted bison for perhaps a millennium until their replacement, the Europeans, arrived with their style of killing frenzy, driving the bison into near oblivion in the 1870s and ‘80s—ironic how the scrawniest predator became the greatest threat. These days killing by the human denizen is restricted to commercialization and licensed hunts. In addition, something wonderful happened in human consciousness, a great awakening. Humans had discovered ecosystems, and how those environmental realms were integral to a human’s well-being. Further, they discovered that the bison was a keystone species to at least one of those ecosystems. Will miracles ever cease! The human predator has been significantly mitigated.
Grizzlies, the polar opposite of scrawny, have been known, according to historical accounts, to kill bison. A grizzly taking down a bison may still occasionally occur in Alaska where bears are more numerous. A buffalo killed by a grizzly, however, is rare. Typically, grizzlies prey during the spring melt on thawing carcasses of bison that had died over the winter .
The wolf is another matter. It is designed in body and behavior to kill hoofed animals. Though the grey wolf is small compared to the buffalo, its numbers more than compensate for size. Wolves hunt in packs from as small as six to as large as a dozen. Essentially, wolves are opportunists, able to capture and eat meat from mice to moose. As such, they will follow buffalo herds until the right opportunity comes along. Following a buffalo herd will often provide the pack’s needs without the necessity of a kill since small mammals are often flushed out by the bison’s feet. But the wolves will watch and target the calves. So adept are packs in taking down calves that the survival of a small herd of bison can be thrown into doubt.
Calves are defenseless by themselves. A cow or bull, though, can easily injure or kill a wolf. A wolf pack may be able to kill a cow or bull in the winter when the bison is in a weakened state, however. A calf only survives a wolf attack with an alert and aggressive mother and/or help from others; though probably not another cow. A bull may be recruited in the defense by the mother leading the calf to the bull, or the calf, on its own, may run to the bull. Typically, the bull will be young, too young to breed, rather than a mature bull. The older bulls are most likely not present. They are probably off somewhere grazing, building up energy for the rut. The primary purpose of a mature bull is to produce as many off-spring as possible. Natural selection, then, has favored the inattentive father so the maximum number of calves will be born.
When the pack’s hunt is successful, the killing is a gruesome affair. Cats kill large prey by suffocation or biting through the skulls of their prey. Dogs do not have this mouth power to kill quickly. Instead, dogs, such as wolves, chew their prey to death, literally eating the prey alive. This is difficult for one wolf to do, but not a pack.
A romantic view, held among some of the supporters of the wolf reintroduction movement, was that of a caring and adorable family life. This is only a projection of human proclivities, however. Life among a wolf pack is not a canine version of the ideal nuclear family, in which mom and dad tenderly care for the young. They are not cute. The wolf-pack life is ruthless and relentlessly structured. Each member lives within a certain pecking order with an alpha male or female at the top. Attempts to reorder the pack are severely treated, even to the point of death. Cruel despotism is perhaps a more apt description, egalitarianism does not exist. Yes, wolves are family oriented, but the structure is about survival and reproduction with each member also having a specific function. The wolf family is also territorial, and will challenge any trespassers with pursuit or death.
The nature of the wolf evolved as a competitor to large predators such as the short-faced bear, the American lion, the American cheetah, the saber-toothed cat and the dire wolf, sharing the North American Plain. The grey wolf was the smallest of these, and the only one to survive the Pleistocene extinction approximately 10,000 years ago. It developed to become a prominent selection factor for diverse characteristics of large mammal fitness. Wolves are highly sensitive to symptoms of weakness in their prey. Victims tend to be debilitated by age, disease or accidental injuries which render them susceptible to the pack. Thus wolves facilitate natural selection by detecting and removing the effects of deleterious genes, and removing the most virulent strains of a pathogen from a prey population .
As the grey wolf was sharpening its hunting skills over the millennia, bison were not idle, however. Buffalo were also evolving their defensive arsenal, including cooperation, defense, escape, and synchronized birthing. The bison herd is a “selfish herd.” Individual animals cooperate with and use other animals to improve their own survival and reproduction odds, ensuring possibly the survival and reproduction of genetically related kind. Bison, then, cooperate to the benefit of all in the herd.
The primary weapons for defense are the horns and the head. Using its powerful neck muscles a bison can hook, lift and toss an opponent. This strategy works best in large herds. By itself, a bison cannot challenge several wolves all at once. For a cow and her calf, alone she is not likely to defend her calf using her head and horns, as the wolves will separate her from the calf, occupying her attention away from the calf. In the herd, however, the bison will form a tight formation with the calves either in the midst of the herd or behind it.
Escape is exactly what it implies. It is the “RUN AWAY!” strategy. Escape involves outrunning and outlasting predators. Bison have adapted physiologically and anatomically for this behavior. Even new born calves are on their feet within 10 minutes and able to run within two hours of birth. Buffalo can challenge all but the fastest horses, yet can out last them, running for many hours over dry, hard prairie ground. There is a selfish component to escaping, though. It’s not just about outrunning the predator. A buffalo only needs to outrun its neighbor. Escaping exposes the weakest individuals, those who lag due to injury, age or disease. Predation selects against the least fit, favoring the evolution and maintenance of strength, agility, endurance and disease resistance. The extreme form of escape is the stampede .
A characteristic of social ungulates such as the buffalo in facing predators is synchronous birthing, which has the dual purpose of predation evasion and optimum utilization of high quality forage for lactation. Due to the behavior of wolves there is little flexibility in the bison gestation period, which leads to a synchronous breeding period. Predators focused on bison calves must take time eating and digesting the hapless prey and spend time traveling to locate the moving herd. Additionally, the number of wolves in an area may be limited by territorial behavior. The number of calves, then, that can be killed by the pack during a short period of time is limited. Bison reproduction has adapted to take advantage of this window of opportunity. The larger the cow herd and the shorter the birthing period, the greater is the probability newborn calves will survive. A cow that breeds during the peak of the rut and calves during the peak of calving, provides the calf with a greater chance of escaping predation .
Wolves not only have the effect of culling buffalo herds through food usage. The reintroduction of the grey wolf in Yellowstone has actually enhanced the growth of buffalo herds. Since the reintroduction of wolves, elk population has declined, opening greater forage and releasing bison from interspecific competition and resulting in higher bison densities . Elk are easier prey for wolves, resulting in lower elk densities and a decreased tendency for wolves to use bison as a food source. The combination of opening more grazing opportunities, and decreasing the predation of bison has allowed for a significant growth in bison populations .
Predation, especially by wolves, has not only enabled bison population growth. Co-evolving with the bison, predation has facilitated the natural selection. Removing deleterious genes and virulent pathogens, the wolf has enhanced the bison’s strength, agility, endurance and mechanisms for preservation. Just as the bison is a keystone species to the Great Plains and the surrounding prairies and forests, so the wolf is key to the health and survival of the bison.
 Callenbach, Ernest. 1996. Bring Back the Buffalo! A Sustainable Future for America’s Great Plains. University of California Press. Berkley. 90.
 Lott, Dale A. 2002. American Bison: A Natural History. University of California Press. Berkley. 100-104.
 Bailey, James A. 2016. The Essence of Wildness: Lessons from Bison. Self-published by James A. Bailey. 24-25.
 Bailey, James A. 2013. American Plains Bison: Rewilding an Icon. Sweetgrass Books. Helena, MT. 63-66.
 Ripple, William J, and Painter, Luke. Effects of bison on willow and cottonwood in northern Yellowstone Park. 15-Jan-2012. Forest Ecology and Management. Vol. 264. 150-158
 White, P. J., and R. A. Garrott. 2005. Yellowstone’s ungulates after wolves–expectations, realizations, and predictions. Biological Conservation. 125. 141-152. See also Ripple, W. J., and R. L. Beschta. 2012. Trophic cascades in Yellowstone: The first 15 years after wolf reintroduction. Biological Conservation. 145. 205-213.
 A line from the movie Young Frankenstein, 1974.
Blakeslee, Nate. 2008. American Wolf: A True Story of Survival and Obsession in the West. Broadway Books. New York.