How Many Footsteps Do Tracking Dogs Need to Determine Direction of a Scent?

A man crosses a football field. Twenty minutes later a tracking dog is brought to the midpoint of the trail and commanded to TRACK. The dog will sniff the area, perhaps back-track a few steps, and then move in the direction that the man walked across the field. How does the dog know which direction the man was moving in? How many footsteps does the dog need to be able to smell to determine the direction the man was walking? Two researchers in Belfast asked these questions and devised an elegant experiment that may have narrowed the possible answers to the first question. As to the second question, the dog cannot reliably tell direction if there are only three steps but it can do so if there are five. Here’s how the experiment was conducted: A dark beige wool carpet was cut into 18-inch squares. Twenty-one squares were lined up and a man walked across them, stepping once on each square. As in the football field, the dogs were brought to the midpoint and told to TRACK. Neither the handler nor the dog had seen the man walking on the squares. The dogs, which had been trained as trackers, reliably went in the direction the man had gone. Two squares were removed so that there were only 19 squares. The dogs were still reliable. Then two more were removed, and so on. The dogs retained their ability to detect the direction of the trail down to five squares, but at three their choice of direction became random. They needed more than three footsteps. Could it be the direction of the footsteps that the dogs used to determine direction? After all, the heel hits before the toe and perhaps this provided a cue. So the researchers mixed up the squares, using a computer program for randomness, but kept the direction of the heel-toe axis of each square facing the same direction as the man had walked. The dogs were not successful in finding the correct direction. They did not seem to be able to rely on general body deposition (the plume of skin flakes, etc.) to determine the direction of the target. The researchers theorized that there is an odor gradient that results from either a stronger smell for more recent tracks that gives the direction to the dog, or alternatively, there is a decay factor which is stronger in the footprints from the direction that the man began at, which the dog used as a signal to move in the opposite direction. The researchers are working on additional experiments to answer more questions about the tracking skills of dogs. D.L. Wells and P.G. Hepper, “Directional Tracking in the Domestic Dog, Canis familiaris,” 84 Applied Animal Behaviour Science 297-305 (2003).