No hunter who’s seen deer halt in their tracks when crossing downwind has questioned the superiority of a whitetail deer’s sense of smell.
Not only do most hunters rank the deer’s nose over its own keen ears and doubting eyes, we also rank it a world beyond our own scent-detecting abilities. Maybe that’s why some hunters think nothing can thwart a deer’s nose. Nonbelievers rudely dismiss an entire industry of odor-killing ozone dispensers; scent-suppressing soaps, sprays and detergents; and scent-trapping clothes and scent-purifying gear bags.
Other hunters, however, aren’t so skeptical. They think we can reduce, but not eliminate, enough human odors to make deer think we’re outside their danger zone. Still, these hunters don’t doubt the deer’s nose. To paraphrase Dr. Grant Woods of GrowingDeer.tv: Humans can smell a casserole cooking in the kitchen, but deer can specify the age, amount and origins of each meat, vegetable and seasoning in the dish. They can probably even gauge the oven temperature, the ingredients’ depth and distribution in the bowl, and how long it’s all been stewing. Deer discern all that from down the holler, not just the hallway.
No one can prove such claims, of course. Professor Karl Miller at the University of Georgia (UGA) doubts science can ever definitively compare a deer’s olfaction capabilities with a human’s. The variables and unknowns of both are too infinite.
Still, we know a few things about the human nose. For one, it’s not useless. A 2007 study by Eric Chudler at the University of Washington estimated our nose has about 30 million receptor sites. Other recent estimates put the number at 10 to 50 million receptors. But before this century, the estimate was 5 million. Whatever the exact number inside our nose, each of those tiny nerve endings is triggered by one specific scent. How strongly we detect an odor depends on how many receptor sites can and do detect it.
Categorizing all those receptor sites by their specific scenting capabilities is difficult, even though humans can describe what they smell. Because of those difficulties, science can’t specify how many odors our nose can detect. Estimates range from “thousands” to 10,000 natural odors, and “infinite” artificial scents.
The bigger challenge, though, is identifying the olfaction capabilities of deer and other wildlife. They can’t just tell us what they’re smelling. Further, Miller knows of no scientific studies mapping the receptor sites in a deer’s nose, let alone categorizing each receptor’s specific sensitivity. Still, deer have far more scent receptors than do humans, and far more types of receptors. Therefore, deer can detect scents we’ll never comprehend.
One early-1990s report estimated whitetails have nearly 300 million receptor sites, but that’s now considered low. After all, recent estimates indicate rabbits have 100 million receptor sites, while most dogs have 1 billion, and bloodhounds 4 billion. Further, the surface area of the “nasal epithelium”—internal nose tissues covered in receptors—measures 9 square centimeters in humans, 21 square centimeters in cats, and 170 square centimeters in some dogs. Bloodhounds top that list at 381 square centimeters, roughly 43 times the surface area inside a human nose.
Although long-nosed animals have far more scent-receptor sites than do humans, the region of our brain that processes olfactory input is more extensive than previously realized. That means we might have extensive brain power for analyzing what we smell, further complicating scent-discerning comparisons with animals. Still, given that researchers in 1981 estimated that a German shepherd’s nose is 10,000 times more sensitive than a human’s nose in detecting a specific raspberry chemical, it’s doubtful our brains can make up such differences.
Meanwhile, the deer’s nose hasn’t received the scientific scrutiny of noses on dogs and humans. Woods, however, thinks the deer’s nose likely tops both. He argues that deer couldn’t have survived their long evolution alongside wolves, coyotes and large cats if their nose wasn’t more sensitive than the predators’ noses.
“Deer would have been wiped out long ago if dogs had the better nose,” he said.
Therefore, it’s conceivable that elk and deer have a billion and more scent-receptor sites, all targeting vast arrays of individual odors. That’s why deer can detect infinitely different scents at once. They can also pinpoint/triangulate each scent’s origins based on how many receptors it triggers, temperature variances inside their nose, and each receptor’s location within their two nasal cavities.
Even if scientists could map a deer’s nose and specify the scent-detection focus of each receptor site, they still wouldn’t know how its brain processes information transmitted by those nerve endings. The physical attributes of a sense’s information source offer clues about what the brain can perceive, but they can’t prove what the brain interprets from that stimuli.
Research 25 years ago into the deer’s eyes had similar limitations. Miller and his UGA students unlocked many mysteries of the rods, cones, retina and other physical parts in a whitetail’s eye. Their findings gave strong clues about the whitetail’s dual-color vision capabilities.
To prove how deer perceived various colors, the UGA researchers had to develop response-based behavioral tests. In those tests years later, deer learned to find their meals based on colored lights above two feed bins. The better the deer perceived a color, the more consistently they chose the right bin.
Researchers had an advantage in testing deer for color vision because humans have tri-color vision, which exceeds the deer’s color-vision capabilities. Because we see colors deer can’t know, we can test how well – if at all – they can see into those color ranges.
We lack that advantage in our sense of smell. Even if we could develop behavioral tests to document what and how well deer smell, our olfaction liabilities could limit what we can verify. We’re probably unaware of countless odors deer regularly smell, so we’re further limited to compare the superiority of their nose to ours. How would we measure what we can’t conceive?
Miller just smiles and shake his head when asked to make “educated comparisons” about the scenting capabilities of humans and whitetails.
“Can a deer smell 10 times better than us, or 100,000 times better? The answer might be yes,” Miller said. “But it might also depend on the odor, humidity levels and air temperatures. It’s impossible to get at all those many factors.”