Yellowstone Wolves Mess with the Wrong Bison Calf

“To say this calf was lucky would be an understatement,” Sypniewski says in an Instagram post. “Separated from the herd, I thought for sure the wolves were on their way to securing an easy meal. Then, seemingly out of nowhere, two adult bison from the nearby herd came barreling onto the scene to protect the youngster, almost trampling the calf in the process.”

Sypniewski was filming the Junction Butte wolf pack in Yellowstone's Lamar Valley.

Sypniewski told MeatEater that he'd been watching this group of wolves for about 30 minutes as they moved across the valley floor. "I saw this female bison about half a mile away and noticed she was in their path of travel. I suspected she had a calf but didn’t know for sure as they were both bedded in tall Sage bush," Sypniewski explained. He moved to a better vantage point and was "just lucky" to capture the scene on video.

The wolves and bison move off-screen after their interaction, but Sypniewski reports that the calf was safely returned to its herd and the adults “carefully escorted the wolves out of the area.” The calf escaped with what Sypniewski believes were minor injuries.

Bison calves aren't always so lucky. Sypniewski says he's seen this interaction play out many times in that section of the park, and the local pack has become "an exceptional bison hunting pack over the years."

"I was very surprised with the way it all turned out. I’ve seen it go the other way many times," he told MeatEater.

Elk constitute the vast majority of an average wolf’s diet in Yellowstone National Park, according to Yellowstone wolf biologists writing in the reference book “Yellowstone Wolves” (2020). But they do feed on bison calves in the spring and summer months.

Bison make up about 10% of a wolf’s diet in the spring, when packs feed on calves such as the one in the video above. That number drops to about three percent in the summer as calves grow larger, but predation on neonatal bison in the spring has increased through time as the relative abundance of bison has increased.

In the fall and winter months, however, wolves have a tougher time with the much larger bovids. Direct predation on bison increases in the late winter as adult bison become weakened through malnourishment and harsh winter conditions, but wolves are almost never able to bring down a healthy, adult bison.

That doesn’t mean wolves have to wait until spring for a bison steak–only that the steak might be a little ripe. Scavenging is how wolves typically acquire bison during the winter, and the growing bison population has offered more opportunities for this opportunistic feeding. In fact, in recent years bison have come to constitute 25% or more of a wolf’s diet during the winter in the northern portions of Yellowstone.

Featured video via Michael Sypniewski.