Joel Berger keeps some photos in his wallet because he knows that the second question he’s going to get — the one after, “What do you do?” — is going to be, “What’s a muskox?”

“Muskox are probably the least studied large mammal of North America,” Berger, a biologist currently with the Wildlife Conservation Society and Colorado State University, tells Inverse. Adults can grow to more than 600 pounds, and they look a little like a hairy, smallish bison. Their name comes from the pungent scent that males emit to attract mates during the rut. While polar bears are certainly the face of climate change’s effects in the Arctic, Berger explains that muskox could be described as the heart or lungs. “Muskox are really a very cold-adapted species,” he says. As the Arctic warms up, the geographic range where the animals can stay comfortable and cool is shrinking.

Which is why Joel plays wildlife dress up.

The Far North is experiencing the effects of climate change much more quickly than the rest of the planet, and Berger wants to know how well muskoxen will be able to adapt. Specifically, he wondered how the animals will react to an increasing presence of polar bears, who will be spending more time on dry land, for want of sea ice from which to hunt seal. So Berger dresses up as a polar bear and chases around mammals three times his size.

“With more stranded of polar bears not making it out onto the ice and becoming landlocked, we know that they occasionally — only occasionally — prey on land mammals,” he says. “We figured that this could be a new dynamic and we wanted to understand it a little bit better.”

Muskoxen have a very different way of dealing with predators, says Berger. “They live in these group-bonded societies, and they are loathe to run.” Running costs energy, and energy is a particularly scarce commodity in the Arctic. So, instead of fleeing, muskoxen will sometimes huddle in a protective circle, horns out, to keep animals who think they look tasty in check. What sort of behavior might they exhibit when threatened by a polar bear, and would this be the same or different from other situations?

In polar bear country, it's best to have a dog nearby. Grigory Nikolaevich

To help answer these question, Berger and a team of scientists set out for Wrangel Island, in the Arctic Ocean north of Siberia, earlier this year for nearly two months of fieldwork. For want of a trained polar bear, he brought the next best thing: a hilarious looking mask. The team braved bitter cold and actual polar bears, all in the name of science. Berger ultimately had to trade the white mitts that came with the costume for a set of red Arctic gloves, in an effort to stave off frostbite.

The plan was to approach groups of muskoxen while wearing the suit, and record their reactions. To make good scientific conclusions, you need decent sample sizes, and waiting around to witness interactions between muskoxen and real polar bears simply isn’t feasible, Berger explains. “When you work in the Arctic, the logistics are huge, the densities tend to be a lot lower, and so getting sample sizes to really cement this as something that’s scientific and not just anecdote — it takes some effort.”

And, in this case, it takes a man in a polar bear suit. There’s a tradition in biology going back several decades of using animal models or costumes as stand-ins to gauge the reactions of other beasts. “It’s actually not that odd,” says Berger. For example, “people have gone to Serengeti and used fake lions to look at how lions will be aggressive to other lions.”

Of course, there’s an element of excitement to being in such a remote part of the world, among such impressive wildlife. But it’s also just a lot of hard work, says Berger. His Russian interpreter found out pretty quickly that this might not be the High Arctic adventure that perhaps he had dreamed of. “I think he realized pretty quickly the tedious nature of what a biologist does in the field. You have to get more samples, more samples, more samples.”

Joel Berger approaches muskoxen in a caribou costume. Sergey Abarok

The other thing you need in science is a control. In this case: a caribou costume. While it’s impossible to say if the muskoxen were specifically thinking “Oh, hey! A caribou! and “Oh no! A polar bear!” it is clear that they reacted differently to Berger depending on his outfit.

Whether they believed he was a polar bear or not, the muskoxen certainly reacted as if he was a serious predator. “They did not find polar bears cute and cuddly,” he says. When he donned the caribou suit, it was a different story. “Sometimes they fled, but they didn’t flee in such hysterics, and they were just calmer when I was dressed as a caribou. They would notice me at a further distance, but caribou of course stand taller, and they’re not white.”

The scientific outcomes of this project are still to be worked out — processing the data involves things like correlating the muskox reaction with snow depth and hardness, which would impact behavior. But in terms of gut feeling, Berger feels that muskoxen are going to learn pretty quickly to stay of polar bears’ way.

“One of the things that is at this point fascinating is that muskoxen seem to be super responsive to polar bears and the potential threat of predation. And so they may be more likely to just get out of the situation — to run.”

Muskoxen on the run. Sergey Abarok

Berger doesn’t believe that polar bears pose a significant threat to muskoxen in a future of climate change. “Both caribou and muskox will be eaten on an ad hoc basis, but they’re fleet, and polar bears are not that fleet, and polar bears warm up pretty fast when they’re chasing things, so I don’t think they are going to be very potent threats.”

But we still know so little about the mighty muskox — how it can adapt and change its behaviors in response to rapidly changing environmental conditions. “The question becomes, what are they learning? How quickly do they learn? And that’s not something that people have focused on.”