In the case of whitetails and mule deer, courtship and breeding behavior is different enough that body language and scent cues given off by a female mule deer during rut are not "understood" by a male whitetail and vice versa. Also, in many areas where their range overlaps, the rut peaks at slightly different times for the 2 species. This system of species segregation has worked remarkably well throughout their evolutionary coexistence. However, in rare cases this system breaks down and genetic material slips across the behavioral barrier, resulting in a deer that is half whitetail and half mule deer. This hybridization between the two different deer species is extremely rare but does occur throughout the West where their ranges overlap.