Let's begin with a mind-boggling fact: in scientific tests, dogs have proved themselves a million times more able than humans to sense certain smells. How is that possible? First, a dog's nose has four times the volume of ours, and while a human nose contains about 5 million ethmoidal (olfactory) cells, some dog breed's noses have over 200 million.

Likewise, the outside of a dog's nose is designed to pick up scents: large and wet, it collects and dissolves scent particles for easier identification. When a dog detects a desirable scent, it reacts by salivating, and the wet tongue also helps to pick up and dissolve more scent particles. Under perfect conditions, wolves have been known to scent deer a mile and a half upwind, and gun dogs sometimes can scent birds a quarter of a mile away.

Dogs can and have been trained to single out virtually any scent--drugs, bombs, gas leaks, and truffles, to name a few. Finding game birds comes naturally to dogs to some extent, but they can also learn to single out the odor of certain birds. For instance, my shorthair used to follow me diffidently through woodcock covers until the day he realized I thought woodcock were game birds and began pointing them for me. He must have smelled them all along, but he paid the scent of woodcock no more mind than the smell of chipmunks, wet leaves, or windfall apples.

Scent and Scenting Conditions

Scent itself is made up of microscopic particles shed by birds and everything else on the planet. Since different objects have distinct chemical compositions, each also has a distinctive smell. If you could see scent, it might look like steam rising off everything in the field, each tendril of vapor intermingling with all the others. How is it that a dog can pick out one scent that matters out of all the smells in the outdoors? Think of a dog's sense of smell as analogous to our sense of sight. A dog would be at a loss to pick a paisley tie out of a rack of stripes and prints, yet we can do it easily. We just know what we're looking for.

To carry on with the analogy of sight: we see better on a clear day than on a foggy one, and dogs detect scent better under some weather conditions than others. Shade, moisture, and cool temperatures help to keep scent particles from drying out. A light breeze carries scent towards a dog downwind.

Dry air and heat evaporate scent and dry out a dog's nose. Rain washes scent away and extreme cold deadens it. Scent clings to soft, moist soil and grass better than to hard, dry ground. Plowed ground and pavement are very poor holders of scent (pavement, apparently, is too smooth). Fog and mist make for good scenting, while cold, dry snow does not. Anyone who's seen a prison-break movie knows you can hide your scent trail by wading up a creek. Strong winds can scatter scent, and in the morning of a cold, frosty day, scenting conditions may be poor until the sun warms the earth somewhat.

A bird's activity, or lack of it, also bears on the ability of a dog to smell it. Birds generate more scent when moving, which explains why dogs have a difficult time finding the birds that hit the ground stone dead, and why the tight-sitting singles from a covey of quail are hard to find, too; dogs will sometimes run right over them without noticing they're there.

In the Field

Understanding scent and scenting conditions will help you hunt your dog more effectively. When you plan your route through a cover, take careful note of the wind direction. Most of the time you'll want to work the dog into the wind, which carries the scent to his nose. At times it pays to take the opposite tack: hunt with the wind at your back, especially with a dog that likes to work far from the gun. He'll range out, then turn to hunt back towards you into the wind. With running birds like pheasants, you pin the birds between the two of you this way.

Pay attention to your dog at all times, not just when the collar beeps the "on point" signal. Learn to read your dog and watch him like a fishing bobber; his every move connects you to the hidden world of birds and scent in the grass beneath your feet. If his casts decrease in amplitude and his head is high, he's picked up a distant scent. Stop and watch what happens, even if it means breaking ranks with the rest of the party.

If a dog puts his nose to the ground and takes off on a line, he's trailing a bird by following the scent left in its tracks; try to keep right with him then, since running birds often flush wild.

On days when scenting conditions are poor, slow down and restrict the dog's range. One very cold, dry day last winter I watched my shorthair point pheasants lying motionless under the snow with a lack of intensity that, with him, usually means a rabbit. In this case, the tentative points meant that he couldn't scent the birds very well. I confined our hunt to a small area, working it over carefully and giving Sam time to puzzle out the faint scents. I shot a limit of roosters over him in under an hour.

All too often I've screamed and whistled futilely at a dog running in what I was sure was the wrong direction after a cripple, only to have him return with the bird. From this I have learned the ironclad rule of dog handling: always believe your dog's nose. That is, after all, why you brought him along.