Above: Behavior of wolves hunting bison: (a) approach, (b) attack-individual, (c, d) capture. “Attacking” is the transition from (a) to (b), and “capturing” is the transition from (b) to (c, d).
Wolves are social animals and hunt cooperatively in a pack.
New research shows that wolves pick their prey based on the wolf pack size and the terrain. We typically think of the phrase, "There's safety in numbers" when it comes to being safe from predators, but, this strategy also works for wolf packs on the hunt.
USU wildland resources assistant professor Dan MacNulty told the Salt Lake Tribune, "Elk are the preferred prey of wolves in Yellowstone. And the reintroduced predators will go out of their way to find their favorite food — and it may not be a matter of taste, but rather their own safety."
MacNulty was one of the authors of a 2014 study published on the peer reviewed website, Public Library of Science. The study titled, "Influence of Group Size on the Success of Wolves Hunting Bison" (journals.plos.org/plosone/article?id=10.1371/journal.pone.0112884) stated that most animals who hunt in groups, including humans, have the most successful hunts in groups of 3-5. But, when it comes to prey that is difficult to catch such as bison, wolves defy the norm by hunting in much larger groups.
The report states, "Bison are the most difficult prey for wolves to kill in North America, and in Yellowstone National Park they are three times more difficult to kill than elk, which are the main year-round prey for Yellowstone wolves.
According to the study, bison are more difficult to kill than elk because they are larger, more aggressive and more likely to injure or kill wolves that attack them. The study says, "As a result, bison require relatively more time to subdue, which is characteristic of dangerous prey. Groups of wolves are more likely to attack bison than are solitary wolves, but the effect of group size on the ability of wolves to capture bison is unknown."