Why dogs sniff: To dogs, the world is not a visual one as it is to us, but instead, it’s a richly odoriferous one.
The sense of smell that dogs possess puts ours to shame. Scientific research has established that a dog’s ability to smell is between 10,000 and 100,000 times more acute than the average human’s.
If the same difference applied to vision, what we are able to see at a third of a mile, a dog could see more than 3,000 miles away just as well.
Dogs are capable of detecting some odours in parts per trillion. This means that while we may notice that our coffee has had sugar added, a dog could detect the same amount sugar in a million gallons of water – equivalent to two pools used at the Olympics. It’s akin to a dog sniffing out one rotten apple in two million barrels.
The stories that abound about dogs are their senses of smell are legendary.
Take the drug-sniffing dog that sniffed out 35 lbs of marijuana in a plastic container swimming in gasoline inside a gas tank, or there’s the black Labrador from Seattle who is able to detect floating whale poo in the sea from as much as a mile away. Cancer sniffing dogs are known to have found melanomas in patients’ skin that doctors had missed.
There is much difference between a human and a canine nose. Dogs have as many as 300 million smell receptors in their noses. We have only about six million. The part of a dog’s brain that analyses smell is 40 times greater than ours, proportionally speaking.
Humans smell and breathe via the same airway channels in our noses. However, when a dog inhales, a fold of tissue just inside the nostril helps separate the smelling and breathing functions.
While all the air that we breathe passes along our main airflow path and our sense of smell is assigned to a small area on our nasal cavity’s roof, with dogs, about 12% of the air passes into a recessed area at the back of the animal’s nose dedicated to the sense of smell. The rest passes this nook down through the pharynx to the lungs.
In the recessed area, odours filter through scroll-like structures called turbinates and the molecules are “sieved” and sorted according to their chemical properties. A dog’s smell receptors “recognize” the molecules by shape and despatch electrical signals to the brain.
Why dogs sniff
When we use our noses to exhale, the spent air goes out the same way it came in and forces out any odours on their way in. However, when a dog exhales, the air gets out through slits in the sides of the animal’s nose. Indeed, this actually encourages new smells to enter the dog’s nose.
It also enables a dog to sniff almost constantly. In one University of Oslo study, a hunting dog who was holding its head high in the wind searching for game was found to be able to sniff a continuous stream of air for as many as 40 seconds.
Although we are not able to wiggle our two nostrils independently, dogs can. This fact, coupled with the aerodynamic reach of each of a dog’s nostrils being smaller than the distance between the nostrils, helps it determine into which nostril an odour arrived. This helps identify a smell’s source.
Nor does a dog’s superiority to a human, when it comes to smells, end there. Dog’s also possess an organ we don’t possess. It’s variously known as the vomeronasal or Jacobson’s organ and can be found at the base of the nasal passage. It is capable of identifying pheromones, which are the chemicals that are unique to each animal species and advertise the mating readiness and other sex-related details of other animals.
The nasal capacity of dogs is one of the fundamental reasons these creatures became man’s best friend.
As an example, take the act of tracking. One Northern Irish study found that dogs who had been brought in at right angles to a trail that had recently been walked by a person could determine the direction that person took by being able to detect minute odour discriminations. In other words dogs can determine direction by the strength of smell from each of the person’s steps. The first step smells less strongly than each subsequent step.
Smell is everything to a dog. It’s the way they have been communicating with each other since the beginning of their time. The fact is that dogs mark the places they think other dogs are going to be with urine. Perhaps there’s something desirable or interesting about that place.
Scent marking is instinctual behaviour for a dog. Other dogs are then able to discern a wealth of information: how many dogs have passed there, how long ago, and if there are any females on heat nearby.
When dogs defecate, pressure on the glands on the sides of the anus causes the glands to expel a musky scent. There are various messages this can impart. It may indicate the dog is scared and alerts other dogs to danger. It could alert another canine that food has been eaten recently and therefore indicate goodies may be close at hand.
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