In November 2015, a big bull elk died in brutal fashion—and David Cross was there to film it. In a video posted to YouTube, a herd of elk runs through field of sagebrush, across a gravel road, and then hurdles over a fence. The video is pretty inconspicuous at first; Most of the animals make the jump over the fence relatively easily. But about 20 seconds in, a giant bull elk runs across the road and then clips its front feet on the top of the fence before flipping forward directly onto its head. The 6×7 elk thrashes its legs briefly before going still. See it for yourself below.

A Migration Expert Breaks Down the Shocking Incident

“I don’t know exactly why the bull elk struggled while the other elk didn’t,” says Dr. Matt Kaufman, the lead scientist of the Wyoming Migration Initiative. “Its antlers did not help in this case. I’m guessing that animal either broke its neck or back because it died fairly quickly. It can be sort of clunky when a bull elk with big antlers takes a spill. I can imagine there’s an increased risk to crossing fences for them compared to cow elk.”

Kaufman specializes in studying the movement of elk, mule deer, and other ungulates in the West. He says that many elk face fence crossings all the time. “On a daily basis, animals are constantly moving around their home range for a variety of reasons,” he says. “On an annual basis, many animals in the western U.S. migrate seasonally from the winter ranges to their summer ranges.”

Kaufman says it’s impossible to tell whether the elk in the 2015 video were migrating. He did note that they were on the run, possibly from being spooked by a car or predator. He adds that it’s uncommon to see animals die in the act of crossing fences. “We really don’t have a quantitative estimate of how many animals die in fence crossings,” he says. “The reason for that is it tends to be fairly rare. The typical way we study these types of things is by collaring a bunch of animals. You could collar a hundred or more animals in a two- or three-year study and have none of them die in fences.”

That said, Kaufman has recorded a handful of fence-related deaths during the course of his research. “Fences are definitely a source of direct mortality,” he says. “But the magnitude of that mortality is small compared to hunting, predators, disease, and winter starvation.”

Kaufman says that the more pressing issue of fencing in the West doesn’t have to do with fence crossing mortalities, but the way that fences can impact the animals’ movement on a broader level. “Fences, especially impassible ones, can have a larger effect by restricting animals’ access to various habitats,” he says. “That’s especially true with ungulates in the West. They can’t crawl under or jump over some woven wire fences. These animals can’t make a good living everywhere. They have concentrated winter ranges in lower-elevation valleys and then many of them migrate, sometimes really long distances, to get up to the high-country where there’s really good summer forage.”

It’s hard to say what the population-level impacts of fences that constrain these migrations are, but in recent years, Kaufman has heard of shocking anecdotal reports. In one case, fencing around a solar power installation in southwest Wyoming pushed a bunch of migrating pronghorns onto a road, killing a number of them. In another, a rancher unintentionally trapped elk on his property by putting up new fencing in the winter. Much of the herd perished when they were caught in a snowstorm.

Many stakeholders are working to utilize wildlife-friendly fencing in the western U.S. Another strategy researchers are using to mitigate the impact of fencing on wildlife is mapping. “Right now, we’re in this Renaissance of mapping migration corridors. The animals in the video probably weren’t on their migration, but the places where fences are most concerning are in their migration routes because you have hundreds of animals moving along the same path,” he says. “Sometimes, they have to cross upwards of 100 fences to get from their summer to winter ranges. Oftentimes the migration routes are fairly narrow. By mapping these migrations and making them available to land managers, wildlife management agencies, and conservation groups, we can identify and address problem spots.”

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As for the herd in the video, Kaufman says that losing the bull elk likely won’t have a significant impact on the herd. “Elk bulls are typically not limiting in populations,” he explains. “There are typically younger bulls in a group that don’t breed. Most likely when you lose that large bull, there’s going to be another one to replace it.”

The video also shows several cows hesitating and deciding not to cross the fence after watching the bull take a tumble. According to Kaufman, that likely won’t be a big issue, either. “Whether fencing can separate herds is not something researchers have been able to evaluate, but I wouldn’t expect it to be a big issue. Several female elk hesitated, but it’s likely they eventually crossed that fence and reunited with the group. These animals have a keen ability to find one another through sign and scent,” he says. “Also, group membership often changes over a season. Some members fall in and out of different groups as they move around.”