If you ask someone what animal has the best sense of smell, chances are that most people will answer “Dogs”. Not a bad answer, though not quite right. At least two others are better.
Dogs have an amazing sense of smell. That's why we use dogs to track and find people who are lost, buried in avalanches, trapped in earthquake- or bomb-damaged buildings. We use dogs to sniff out illegal drugs, explosives, buried landmines, soil contaminants, animals of specific endangered species, black truffles, and even diseases. They couldn’t do it without their remarkable ability to smell. But what’s also significant is that dogs are so willing to be trained for these tasks. Some other candidates with great noses are less convenient and obliging. More on that, later.
Why are dogs are better at smelling than human?
· Humans have 5-6 million smell receptor cells in our noses; dogs 100-300 million.
· The area of the brain devoted to processing smells is 40 times larger in dogs than in humans.
· Dogs have a special organ — the “Jacobson’s Organ” devoted to processing smells. We don’t.
· As humans breathe in, we get new smells. As we breathe out, nothing. As dogs breathe out, their breath causes some turbulence which pulls new scents into the smelling area of their nostrils.
· Dogs can distinguish whether smells are coming from their left or right nostril. The difference of smell between the two nostrils lets them know the direction a smell is coming from.
Professor Alexandra Horowitz, head of the Dog Cognition Lab at Columbia University summarizes a dog’s ability to smell: “while we might notice if our coffee has had a teaspoon of sugar added to it, a dog could detect a teaspoon of sugar in a million gallons of water, or two Olympic-sized pools worth.” Alexandra Horowitz has written a number of fascinating books about dog cognition, most recently The Year of the Puppy, and Our Dogs, Ourselves.
Dogs can identify the intensity of a smell with incredible sensitivity. By smelling 5 footprints they know which are less intense and therefore older. From this they know which direction the person was walking.
Scientists also believe that this is how dogs know when to expect owners back from work. If the owner has a regular routine and returns, say, 9 hours after leaving, the dog knows that when the owner’s smell has dissipated to a 9-hour-old level, it’s time for their return. Ingeniously, this hypothesis was tested by quietly reinforcing the owner’s scent during the day, by introducing clothing worn by the owner. Dogs who habitually waited at the front door at the right time, were fooled.
For dog owners it’s important to understand that dogs’ sense of the world is primarily through smell, not sight, as ours is. Your dog will be happier and better adjusted if you allow it to spend a lot of walking time following the interesting smells which are all around. And which you are unaware of. When we meet people, we naturally look at them to get a sense of who they are. Dogs smell each other to get that. Females tend to smell the front end of other dogs; males the back ends. By smelling they can tell the age, gender and health of the other dog. And more – like sexual attractiveness. But while we need the person present to see that information, dogs can smell that information by sniffing where the dog has been. When dogs sniff a tree, hydrant or telephone pole, they’re identifying who has been there. And when they pee on it themselves, they’re leaving a message to say “I was here”.
By the way, our vision is not just better than dogs’ — it’s better than most of the animal world. Eagles can see more acutely than we can (“eagle eyes” is an apt expression), but few others even come close.
So what animals out-smell dogs? In hindsight it’s not surprising. Elephants’ noses are astonishing, not just for being long, but for being sensitive.
Elephants have been known to smell water from a distance of 20 km. They were tested for their ability to smell after it was noticed that they avoided land mines in Angola. Elephants can smell the difference between people from two Kenyan tribes: the Masai, who traditionally hunt elephants and the Kamba, who don’t. Elephants have been tested on their ability to tell, by smell, the quantity of sunflower seeds in a bucket with a perforated lid. The elephants consistently choose the fuller container.
In a really interesting experiment, described by Ed Yonge in his fascinating book An Immense World, scientists tested the ability of elephants to tell the identity of other elephants by the smell of their urine. The scientists would follow a herd of elephants and wait for one of them to pee. Then they would scoop up the pee-soaked earth, guess where the herd was headed, and dump that earth in the expected path. When the elephants reached that area, they would smell the pee-soaked earth. Those elephants who were walking ahead of the donor of the specimen were clearly confused by it. It was obvious that they knew whose pee they were smelling, but that individual was behind them, so couldn’t have just peed in front of them.
The other animal that can out-smell a dog is a bear. There are lots of stories about bears being able to smell animal carcasses from huge distances (some say up to 32 km), and male polar bears have been known to trek 100 miles (160 km) following the scent of a sexually receptive female.
But for very practical reasons we do prefer using dogs to help us with smell-related tasks, rather than elephants or bears.
