The first report of urine overmarking of pro-oestrus female dung by a male white rhino

Although observed in other Perrisodactyla, urine overmarking in white rhinos has not been described. Using a single opportunistic sighting, we were able to collect two dung samples from one oestrous female white rhino; one unmarked and one overmarked with male urine. Because of the behaviour of both the male and the female, we suggest that the female was in pro-oestrus. We hypothesised that the function of overmarking by the male was for oestrus concealment (i.e. odour masking), as observed in horses. Because dung from oestrous female white rhinos emits a higher proportion of alkanes than non-oestrous dung, we expected the proportion of alkanes emitted from oestrous dung to decrease after overmarking. In contrast, we found that after overmarking the proportion of alkanes emitted increased. We suggest that the function of urine overmarking in white rhinos could be to conceal all signals of reproductive condition, so that neither oestrous nor non-oestrous signals are recognisable, or that a signal is added to indicate that the female has been mated.