The baby muskox is in the running for cutest animal on Earth. It staggers around on chubby legs like a toddler in fuzzy white socks exploring new terrain. Its rounded face is short-snouted, with tiny half-moon ears and guileless white lips. The downy black body brings to mind a favourite stuffie.

Its parents’ forbidding shoulder hump and upper-body heft have not yet formed, nor its up-pointed, semi-circular horns or the hard plate of bony horn on the adult male’s head, carefully parted in the middle as if it were sitting for a 19th-century portrait. The newborn is perhaps cutest of all in contrast to its mother, whose massive body, fringed in long fur, seems precariously perched on petite, knock-kneed legs.

Brynn Parr, a Nome-based wildlife research biologist with the Alaska Department of Fish and Game, has spent a lot of time with baby muskoxen. “They are adorable,” she says. 

And then there’s the quizzical muskox social structure. Muskoxen live in groups, often of a few dozen. When a predator, such as a wolf, attacks the group, the adults form a circle around the young, bums in, horns out. If needed, one of the adults, either male or female, charges the predator. But which one?

“Is there a hierarchy that we don’t understand yet?” Parr asks. “Is there a trigger that sets off a cow versus a bull?”

It’s not just the unknowns. It’s the weirdness, too. The muskox looks like a mammoth cousin that has arisen, Lazarus-like, out of a sheet of ice. With Miocene-era ancestors that wandered the tundra about 12 million years ago, muskoxen are often thought of as prehistoric.

“On the landscape, it looks like they’re out of time,” Parr says. “And you just kind of feel like you’re next to a piece of living history.”

Maybe it’s that otherworldliness that has people flummoxed. In some unarticulated way, we’re surprised that muskoxen have survived at all.

When you are a large, black, cold-adapted ruminant that doesn’t move much, climate heating is not just unpleasant — it can also be dangerous. Consider that muskoxen get only about six weeks of good foraging toward the end of an Arctic summer, during which time they have to pack on enough weight to carry them much of the way through the year to come. For females, that includes gestation and nursing. 

They gobble up grasses, willows and sedges, which go into the rumen, the largest part of the muskox’s four-chambered stomach. (Thus the name ruminant.) That’s where bacteria, fungi, protozoa and other microorganisms ferment the plants, breaking down the cellulose and turning it into sources of energy and protein the animal can use. 

When the muskox gets too hot, those microorganisms undergo changes, Gunn explains, noting that much of the research on muskox digestive physiology is extrapolated from studies on cattle and sheep rather than direct evidence from muskoxen. The changes to microorganisms set off a cascade of effects. Fermentation slows down. The animal is too full to keep eating. Precious weight-gaining time is lost. This can have a direct hit on the birth rate. If a pregnant female finds herself too thin by fall, her body will reabsorb the embryo rather than carrying it to term. 

“Give them minus 20 [degrees Celsius], they’re great,” says Susan Kutz, a professor in the University of Calgary’s Faculty of Veterinary Medicine. “Plus 20, they’re not as good.” Kutz, the Canada research chair in Arctic One Health who has spent years studying how infectious diseases affect muskoxen, has confirmed several grim trends that accompany the warmer Arctic. Higher temperatures alter vegetation and the availability of some of the trace nutritional elements muskoxen need. On Kitlineq (Victoria Island) and Kuuganajuk (Somerset Island), for example, she believes muskoxen are short of trace minerals such as copper and selenium that are critical for growth, reproduction and immunity. Among the unknowns are exactly which plants are most important for these minerals, or even how climate change affects the dynamics of minerals in plants. 

But even while their immunity is increasingly compromised, a virulent new disease is showing up. Kutz and her colleagues have discovered what appears to be a highly deadly strain of the bacterium Erysipelothrix rhusiopathiae that has ravaged muskoxen on both Kitlineq and Banks Island. The strain is unique to the Arctic and is likely one factor in the recent population crashes there. It’s unclear exactly what role climate heating plays, but the first two outbreaks Kutz chronicled happened a couple of weeks after unusually hot temperatures.

E. rhusiopathiae has been around in the Arctic for decades in some form or another. Farther south, it’s common in poultry and pigs. It’s known as an opportunistic pathogen, which means it can wait around until an animal is wounded or immunologically compromised. Then, it pounces. In muskoxen, the pathway is unusually lethal. The bacteria invade the bloodstream, leading to septicemia and then shock, rapidly followed by death.

The carcasses Kutz and her team examined were of muskoxen of all ages, all well fed and rudely healthy — except they were dead.

And it’s not as if the muskox can keep moving in search of fewer predators and more cold. Look at a map of the world’s most northerly islands, and most of them are already home to muskoxen. Soils tend to be poor across the Arctic archipelago, ruling out prospects for good foraging that could support more animals. “I don’t think really there are any new habitats that will open up for them,” Kutz says.

In Canada, they’ve already reached the top tip of Umingmak Nuna (Ellesmere Island), our most northerly territory. Even on that island, some of the muskox populations appear to have been in decline since 2021 because of E. rhusiopathiae, Kutz says. The high death rate is an awful echo of what happened on Kitlineq and Banks Island.

Instead, muskoxen seem to be recolonizing some of the more southerly regions they lived in before they were nearly wiped out in the late 1800s and early 1900s. This Arctic icon has moved far south of the treeline in the Northwest Territories and has even been sighted in northern Alberta and Saskatchewan. While those areas are not as amenable to cold-adapted animals, they may provide some better foraging and patches of shade for relief from the sun. But population surveys have been rare or absent, so it’s hard to know exactly how those expanding populations are faring. Are their numbers on a sharp upswing only to be followed by a decline?

“Those are areas that are being or have been recolonized over the last 20 to 30 years. And so we see this thing where [the numbers] go up, and who knows how long that will last?” Kutz says.

That’s another standout feature of muskoxen: how loosely they are monitored. The Ambio paper found that information on 35 per cent of the global population is so scarce that an assessment on trends for those groups is impossible. Canada, the global heart of muskox territory, does no regular aerial surveys. Nor is there national oversight.

“I think we’ve all been lulled into a false sense of security,” Kutz says.