Urine Marking Wild rats leave odor trails during their movements about the living space. Where they run regularly over a light surface they leave a dark smear. Reiff has shown that urine and genital secretions contribute to the odor trails, and that the trails are followed by other rats. In artificial colonies the trails always have an attractive effect, even when the rat is a newcomer to the enclosure and to the colony. Hediger, in his excellent study of wild animals in captivity, suggests that the scent marks left by many mammals at fixed points in their territory are deterrents to other members of their species, comparable to bird song and other displays; but it is uncertain whether this is ever their function in fact. It is evidently not so for wild rats. Perhaps the marks have a mnemonic function; they may help an animal to remember it's way about. Scent marks or trails may help all members of a colony in common. Source: the book "The Rat: A Study in Behaviour" by S.A. Barnett