Individuality, species-specific features, and female discrimination of male southern white rhinoceros courtship calls.

Male vocalizations associated with courtship can play a key role in mate selection. They may help females obtain information about males' quality and identity and/or may contain species-specific properties that help prevent interspecies breeding. Despite vocalizations being a prominent part of the courtship of white rhinos, the role that they play in white rhino breeding behaviour has not been extensively studied. Both southern (SWR) and critically endangered northern white rhino (NWR) males intensively vocalize during courtship with hic calls. We examined these calls and found that call properties differed between NWR and SWR males. In addition, we found that individual SWR males could be identified with a high degree of accuracy using their hic calls and that the signature information capacity in hic calls would allow females to individually recognize about 11 adult males living in or moving through their home-ranges, which may help with mate selection. Then, we conducted playback experiments with wild anoestrus SWR females. The females discriminated between the NWR and SWR hic calls and between the SWR hic and SWR pant calls. However, we only found differences in the latency of observed behaviours, not in their duration or in the intensity of females' reaction. This might suggest that females which are not in oestrus are not highly responsive to a male's motivation (i.e., seeking contact or mating), but are more interested in assessing his dominance status or familiarity. Ultimately, our results indicate that courtship hic calls encode information which might help females choose mating partners.

Sex and species recognition by wild male southern white rhinoceros using contact pant calls.

Recognition of information from acoustic signals is crucial in many animals, and individuals are under selection pressure to discriminate between the signals of conspecifics and heterospecifics or males and females. Here, we first report that rhinos use information encoded in their calls to assess conspecifics and individuals of closely related species. The southern (Ceratotherium simum) and critically endangered northern (C. cottoni) white rhinos are the most social out of all the rhinoceros species and use a contact call pant. We found that southern white rhino pant calls provide reliable information about the caller's sex, age class and social situation. Playback experiments on wild territorial southern white rhinoceros males revealed that they responded more strongly to the pant calls of conspecific females compared to the calls of other territorial males. This suggests that pant calls are more important form of communication between males and females than between territorial males. Territorial southern males also discriminated between female and territorial male calls of northern species and reacted more intensively to the calls of northern than southern males. This might be caused by a novelty effect since both species naturally live in allopatry. We conclude that white rhinos can directly benefit from assessing individuals at long distances using vocal cues especially because their eyesight is poor. Pant calls thus likely play a significant role in their social relationships and spatial organization. In addition, better understanding of vocal communication in white rhinos might be helpful in conservation management particularly because of their low reproduction in captivity.

Discrimination of familiarity and sex from chemical cues in the dung by wild southern white rhinoceros.

Communication in rhinos is primarily mediated by the vocal and olfactory signals as they have relatively poor eyesight. White rhinos are the most social of all the rhinoceros species, they defecate at common dungheaps and the adult bulls use dung and urine to mark their territory. Chemical communication may therefore be particularly important in the social interactions of white rhinos, and its knowledge could be very helpful in their management and conservation. However, no studies have investigated up until now the olfactory discrimination in any rhinoceros species in the wild. We have experimentally studied the reactions of the wild southern white rhinos (Ceratotherium simum) to the dung of familiar and unfamiliar adult females and adult territorial males. We registered the number of sniffing events, the duration of sniffing and the latency of the vigilance posture from the onset of sniffing. The dung of unfamiliar rhinos was sniffed longer than that of familiar rhinos. The rhinos showed a shorter latency of vigilance posture to the familiar dung of males than that of females. For unfamiliar dung, they displayed a shorter latency of vigilance posture to female than male dung. Our results indicate that the rhinos are able to discriminate the familiarity and sex of conspecifics from the smell of their dung. Olfactory cues could therefore play an important role in the social relationships and spatial organization of the southern white rhinoceros.

Contact calls of the northern and southern white rhinoceros allow for individual and species identification.

Inter-individual relationships particularly in socially living mammals often require a well-developed communication system. Vocal and olfactory signals are the most important for the communication of rhinos, however, their vocal communication has been investigated to a very limited extent so far. White rhinos have the most developed social system out of all the rhinoceros species and vocal signals might therefore play an important role in their social interactions. We recorded repetitive contact pant calls from six captive northern white rhinos (Ceratotherium cottoni) and 14 captive and free-ranging southern white rhinos (Ceratotherium simum) and examined if they transmit information about individual identity, species, social context and age class. Discriminant analyses revealed that a high percentage of the pant calls of both species could be classified to a correct individual. We calculated signature information capacity of pant calls recorded from adult animals in isolation at 3.19 bits for the northern white rhinos and at 3.15 bits for the southern white rhinos, which can potentially allow for a vocal discrimination of nine individuals of both species. We found that pant calls varied by species. Northern white rhinos had longer calls and also differed from the southern white rhinos in several frequency parameters of their calls. We also analysed the pant calls of southern white rhinos for the differences between the age classes and between social contexts in which they were recorded. Our results show that pant calls carry information about individual, species, age class and context. The ability to recognize this information would allow rhinos, in addition to olfactory cues, to communicate with highly increased accuracy. A better understanding of communication of white rhinos has potential practical use in their management and conservation particularly because of the low breeding success of white rhinos in captivity.