Dogs are able to determine the direction a track goes. This makes sense when you think about it. If a dog was not able to determine the direction of the track, then a dog hunting prey might end up wasting precious time tracking away from their target. If you understand anything about scent you would also know that it decays over time. Now, a number of things affect the rate of decay but it is supposed that it is this decay that allows the dog to determine the direction of the track.
Hepper & Wells (2005) used 21 carpet squares layed out in a line and then had a single person walk across the carpet one step per square (which I think is pretty cool). They found that it took 1–2 seconds for the odour information in footsteps to change enough that the dogs tested in their research were able to determine direction. They also found that dogs can determine direction from five steps (or more) but were unable to determine direction form only three. Finally they showed that dogs can determine direction of a track from direct contact footsteps but not indirect fallen body odour cues.
What are direct contact and indirect fallen body odour cues you might ask? There are two odour cues left when an individual walks: a direct contact cue that arises from the bottom of the shoe touching the ground; and a more indirect cue from body odour that falls to the ground. In this research by Hepper & Wells (2005) the dogs tested were not able to determine direction of track using the indirect fallen body odour cues alone without the direct footstep cues. But, they were able to determine direction of track with the direct contact cues alone (no indirect fallen body odour cues). This is a very interesting finding, particularly when you are thinking about different surface tracking and variable environmental conditions.
So the answer to the question how many steps do dogs need to determine the direction of a track is FIVE steps, and they don't need body odour to do it.
There are a number of research papers looking at a dogs ability to determine the direction of track. The researchers have had varying results. Interestingly all the papers I have come across use trained tracking dogs (ie dogs trained to track humans) and not hunting dogs. I think it would be interesting if someone would do some research using hunting dogs (dogs trained to hunt down animal prey) as they are much less restricted in their training and obedience and are more intinctual.
Hepper & Wells (2005) used 21 carpet squares layed out in a line and then had a single person walk across the carpet one step per square (which I think is pretty cool). They found that it took 1–2 seconds for the odour information in footsteps to change enough that the dogs tested in their research were able to determine direction. They also found that dogs can determine direction from five steps (or more) but were unable to determine direction form only three. Finally they showed that dogs can determine direction of a track from direct contact footsteps but not indirect fallen body odour cues.
What are direct contact and indirect fallen body odour cues you might ask? There are two odour cues left when an individual walks: a direct contact cue that arises from the bottom of the shoe touching the ground; and a more indirect cue from body odour that falls to the ground. In this research by Hepper & Wells (2005) the dogs tested were not able to determine direction of track using the indirect fallen body odour cues alone without the direct footstep cues. But, they were able to determine direction of track with the direct contact cues alone (no indirect fallen body odour cues). This is a very interesting finding, particularly when you are thinking about different surface tracking and variable environmental conditions.
So the answer to the question how many steps do dogs need to determine the direction of a track is FIVE steps, and they don't need body odour to do it.
There are a number of research papers looking at a dogs ability to determine the direction of track. The researchers have had varying results. Interestingly all the papers I have come across use trained tracking dogs (ie dogs trained to track humans) and not hunting dogs. I think it would be interesting if someone would do some research using hunting dogs (dogs trained to hunt down animal prey) as they are much less restricted in their training and obedience and are more intinctual.