[aigel]

I have spent significant time behind big game hounds and also blood tracking dogs, some of them my own. It is very fascinating. The dogs are direct descendants of the wolf, so it isn't terribly surprising that they can track well, it isn't a taught behavior ...

What you have to understand is that the dog follows a multitude of signals and puts them together to get the whole story - it is not all the scent of the animal. Experienced dogs will look for physical imprints of tracks and follow them with their eyes. They also do not need scent of the animal or human they follow to be present at all times - the ground and plant life is upset and squished by footprints themselves and this scent brought out is enough for the dog to follow. All it needs is a whiff every now and then to confirm it is following the right track. Literally a few molecules will suffice. Don't forget that any animal and human sheds pieces of skin and coat at all times ...

Dogs generally are able to also tell if they are going the right direction. They can age a track and will turn around if they notice that it is getting colder instead of hotter in the direction they are going. Smells are made up from substances of different volatility - the more volatile smell component will evaporate first - making the track smell older with time.

Another component you don't see is that the dogs can lose a track for quite some time. If they do, they generally range out from where they smelled it last and try to pick it up again, returning to the spot they smelled it last frequently. This is how they can easily get across any hurdle like someone walking in a river for a couple hundred yards or the track going across a very sunny area where it evaporated out more quickly.

Finally one thing I see a lot is that the dogs pick up the smell not from the foot track rather than the brush and tips of grass. These rub against the body of the animal / human which carries a lot more smell than the feet.

Cheers,

George