A Canine Sense of Smell

A repost from this blog circa 6-30-05.

Canine noses are so amazing that we humans rely on them for a host of important things, from ferreting out smuggled drugs, to bomb detection, from locating fire accelerants to termite detection, from catching escaped criminals to finding lost children.

On Guam, Jack Russell terriers are used to smell out snakes, while rescue beagles are used at international airports to find smuggled fruits and sausage. Dog noses are employed for rescue work during disasters and to locate birds in thickets, to say nothing of dogs trained to smell out human cancers and even diagnose schizophrenia.

The power of the canine nose is derived, in part, by the large number of olfactory receptors (about 25 times the number we humans have), the much larger nasal cavity of dogs (about four times larger than that of humans), and the larger olfactory lobe within the canine brain which registers and records scents (much larger than humans even though we have a bigger brain).

Dog can sense odors at concentrations nearly 100 million times lower than humans can, and can detect scents as faint as one drop of blood in five quarts of water.

It appears that dogs trained to detect specific scents actually "ping" on certain sub-sets of the scent. Very small trace elements in gasoline, for example, may be the real "scent" the dog is looking for, rather than the potpourri of scents we humans associate with petrol.

Dogs can follow concentration gradients of scent molecules to determine which direction an animal has gone, and the relative strength of the scent will tell the dog how recently the animal went by -- the basis of all scent tracking by dogs.

Scent is incredibly important to many animals, and a key element in the daily life of the fox, wolf and coyote. Urine, scat and anal gland markings are all scent-based communication elements. With a sniff or two a fox, wolf, or coyote can know not only what species of animal has gone by, but its relative size and health, its sex, and age.

Fox will urinate and often defecate on prominent rocks and ledges on the edges of their territory, and if you see a rock poking out of an otherwise flat field, it's worth a look to see if there is a tapered bit of fox scat on top. Fox will lay down more scent markers around particularly fruitful hunting areas, such as ditch banks -- a way of pointedly declaring a valuable hunting ground as "off limits" to other fox.

Bottled fox urine is sold in hunting stores so that deer hunters can spray it on their shoes to mask the scent of humans, and it is also used by trappers to mask human odor and to attract fox to the general vicinity of a set. Fox and coyote urine on small sponges afixed to popsicle sticks can also be used to deter rabbits and other small animals out of vegetable patches (though this may not work for too long).

If you are training a puppy to pee in a certain area, fox urine can also help with this chore -- the dog will instinctively lay down its own mark over the fox scent in order to "claim" the spot as its own.
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