Detecting and locating prey through depositional odor trails
There are two ways predators can use odorants to locate prey. The first is airborne odors, and the second is depositional odors that lie on the ground or other surfaces. The latter are chemicals sloughed off by an animal as it moves along the ground and airborne chemicals that have settled out of the air column and lie on surfaces. If undisturbed by airflow or precipitation, then deposited chemicals may lie undisturbed on a surface for hours or days, allowing an animal to detect the earlier passage of another. However, predators cannot smell depositional chemicals as long as these chemicals remain on a surface; instead, the chemicals must be resuspended into the air to be detected. A predator can accelerate this resuspension of odorants by placing its nose close to the ground and inhaling rapidly. This creates an air current along the surface that causes the odorants to be resuspended and inhaled. Beagles can use depositional odor trails to track and run rabbits for miles (DiBenedetto 2005), and trailing dogs can follow the path made hours earlier by a person (Johnson 1977; Lowe 1981). Such formidable olfactory abilities are used by predators to locate and track their prey.