Discrimination of sex and reproductive state in koalas, Phascolarctos cinereus, using chemical cues in urine

Although marsupials have well-developed olfactory systems and complex scent-marking behaviours, relatively little is known about the actual function of chemical signals in this group of mammals compared to eutherian species. In this study I investigated whether koalas are able to assess the sex and reproductive state of signallers using chemical cues present in urine. Male urine induced more chemosensory investigation by males and oestrous females than female urine, and nonoestrous female koalas displayed an aversion to male urine. When presented with oestrous versus nonoestrous female urine, males but not females displayed a significant investigatory preference for oestrous urine. Taken together these results indicate that koala urine contains chemical cues permitting the discrimination of sex and female oestrous stage. These findings also add to a growing body of literature showing that chemical cues serve to advertise female reproductive state in mammals, and the first clear evidence of this in a marsupial.