Data from: Influence of group size on the success of wolves hunting bison

An intriguing aspect of social foraging behaviour is that large groups are
often no better at capturing prey than are small groups, a pattern that
has been attributed to diminished cooperation (i.e., free riding) in large
groups. Although this suggests the formation of large groups is unrelated
to prey capture, little is known about cooperation in large groups that
hunt hard-to-catch prey. Here, we used direct observations of Yellowstone
wolves (Canis lupus) hunting their most formidable prey, bison (Bison
bison), to test the hypothesis that large groups are more cooperative when
hunting difficult prey. We quantified the relationship between capture
success and wolf group size, and compared it to previously reported
results for Yellowstone wolves hunting elk (Cervus elaphus), a prey that
was, on average, 3 times easier to capture than bison. Whereas improvement
in elk capture success levelled off at 2–6 wolves, bison capture success
levelled off at 9–13 wolves with evidence that it continued to increase
beyond 13 wolves. These results are consistent with the hypothesis that
hunters in large groups are more cooperative when hunting more formidable
prey. Improved ability to capture formidable prey could therefore promote
the formation and maintenance of large predator groups, particularly among
predators that specialize on such prey.