Fat Bear Week: Bears sense the world in an extraordinary way

Inside a bear’s snout lies an extraordinary world.

The ursine nose is lined with a vast sheet of specialized tissue, called the epithelium, which is embedded with scent-detecting nerves. Like the human epithelium, these cells have the exceptional ability to regenerate themselves (unlike most other nerves). But a bear’s epithelium dwarfs our own. “It is much, much larger than a human’s,” explained Heiko Jansen, a neuroscientist who researches human and animal physiology at Washington State University. “It’s several orders of magnitude larger.”

And lying above a bear’s great muzzle, scrunched under the brain, sits the olfactory bulb — a tube-shaped structure that connects a bear’s profusion of nose nerves to other parts of its brain. Jansen’s measured this brain structure. It’s about five times the size of a human’s.

Though research on bear olfaction is scant, the consequence of this highly-evolved scent architecture is indisputable.

“It’s obviously clear to everybody that bears have a great sense of smell,” said Jansen.

“I would characterize a bear’s sense of smell as complex and just as important to their lives as sight is to humans,” said Mike Fitz, a former park ranger at bear-filled Katmai National Park and Preserve and currently a resident naturalist for the wildlife livestreamers explore.org.

Bears’ dependence on extraordinary olfaction creates a reality that we can imagine, but never truly know. Their very existence might be swamped in potent odors.

“It’s a different world,” said Andrew Derocher, a polar bear biologist at the University of Alberta.

Katmai National Park’s Bear 747 sniffing around his realm.
Credit: NPS / B. MOSBROOK

What sort of world?

It’s a world in which you may be roaming through a river or Arctic plains by yourself, but you would have a firm awareness of the presence of other bears (or anyone else) around you, even if they’re nowhere to be seen. The presence of others wafts through the air.

“You’re never really alone,” said Derocher.

It’s a world in which information about other individuals is stored on the ground, trees, and grass, long after they’ve gone elsewhere.

“Sound and sight are ephemeral,” noted Fitz. “Scent lingers far longer. I could travel through an area and piece together stories of who was there prior to me without having to see or hear them.” 

Polar bears, for example, will cross a trail of bear prints and promptly sniff the frozen earth. In some cases, the male bears will turn around, perhaps sensing a dangerous or uninviting meeting with another bear. But if they perceive a potential female mate, “they’ll follow [the scent] like crazy,” said Derocher.

“You’re never really alone.”

Male brown bears have adopted a similar strategy. The bears obsessively pursue a female’s scent if they perceive she’s in heat. It becomes a drawn-out chase, often through dense forest. “The male can use his powerful sense of smell to follow her path almost exactly even when he can’t see her,” said Fitz.

It’s a world that would disturb or overwhelm us.

“If I were suddenly endowed with a superpower like a bear’s sense of smell, I think I might be shocked initially by the world of odor,” said Fitz.

Perhaps daily life for a bear is like perpetually walking around a piquant landfill, a fish market, or a New York City subway car in sweltering July. Or maybe it’s more like a perfumery.

It’s a world we’ll never quite understand.

“We find certain things revolting based on smell — other animals just find them irresistible,” said Jansen, noting animals that eat their own poop.

Katmai National Park Bear 480 “Otis” and his big muzzle.
Credit: nps / n. Boak

Bear skull showing where olfactory neurons lead to the brain’s olfactory bulb.
Credit: Heiko Jansen

Indeed, we don’t ever know what animals are truly thinking, what they understand, and how they view the world through their lively eyes and large nostrils.

“What would it be like to smell like a bear?” asked Jansen. “I don’t think we would ever truly know.”

But we do know that bears have olfaction powers perhaps many times stronger than bloodhounds. “[Bears] are probably more sensitive than a bloodhound to smelling different things,” Jansen noted.

Knowing just how powerful this olfaction is, though, is an open question.

“We know bears have an excellent sense of smell but there are few studies that quantify just how good it is,” explained Derocher.

That leaves room to wonder.

“You hear all sorts of stories,” mused Jansen, “like bears can smell a carcass from miles away.” “There’s probably some truth to that,” he added. “But there hasn’t been a lot of scientific research to back up those assertions.”

But one thing is certain. Bears rely on scent for survival. That’s because they must get fat. They only have a limited amount of time to amass fat reserves before the great, annual winter famine, also known as hibernation, begins.

“When it comes to bears it is survival of the fattest,” Derocher said emphatically.

“Their whole lives revolve around food,” said Jansen. “They have to get fat in the fall and hibernate. It’s no surprise that a lot of what they do is based upon their sense of smell.”

“It is survival of the fattest.”

Bears often stand erect in the wild, with their muzzles extended into the air to “see” what’s out there. The winds may carry hints of a meal in the distance, perhaps miles away. “Bears are working the winds all the time,” noted Derocher.

Without bears’ extraordinary ability to not just perceive scent — but understand a wealth of information stored in those scents like a thumb drive — the large omnivores (some well over 1,000 pounds) might not survive in the harsh, competitive wilds.

“If you’re a bear and you lost your sense of smell, I don’t think you would be a bear much longer,” said Derocher.

This story was originally published in October 2019.