We already know a lot about elephant trumpeting, dog barking or horse neigh, but we have never been taught what do the rhinos say. In addition to olfactory perception, vocal expressions are usually the most important way for mammals to communicate. For rhinos, only the basic features of communication have been described so far, although white rhinos have the most developed social system and thus also the widest vocal repertoire of all species of rhinos.
Due to the extremely high risk of extinction, rhino studies are an increasingly relevant topic. The authors, among others from the CULS Faculty of Forestry and Wood Sciences – Department of Game Management and Wildlife Biology, decided to expand the existing knowledge and in their research focused on the contact call of two species of white rhinos group – the white rhinoceros (Ceratotherium simum) and the recently differentiated northern white rhinoceros (Ceratotherium simum cottoni).
The northern white rhinos are currently on the verge of extinction. At the time of the research, only 7 individuals survived in captivity (they have already become extinct in the wild)! White rhinos are much better off (20,000 individuals in the wild), however, their population is threatened by extensive poaching. Up to 1000 pieces per year die in order to obtain a horn. The main difficulty in rescuing the northern white rhino is its extremely low ability to reproduce in captivity, the causes of which are not well known. Some studies point to the possible influence of complex social ties, which do not allow mating between the remaining individuals. Studying mutual communication can be especially useful for understanding rhino interactions and could help save an almost extinct species at the last minute.
The research itself took place in various zoos in Europe, including the Dvůr Králové ZOO, and in South African reservations. A directional microphone was used to record the calls of rhinos, and the obtained recordings were subsequently analysed by special programs for bioacoustics analysis. The duration of individual calls, their frequency or the number of inhales and exhalations were recorded. Both species of rhinos have a unique vocal expression consisting of a series of wheezing to squeaking sounds. The authors found that their call contained specific information that differed both between the two species studied and between specific individuals. Based on this call, different individuals can be identified, just as criminal investigators identify the suspect's voice. Differences were also found depending on the age category or social status in the group. The call made in isolation contained more elements than on visual contact with the rest of the group, just as the males in the presence of a competitor sounded differently than when they were the only ones in the herd.
A better understanding of rhino communication has potential practical application for their management and rescue. Currently, the authors are analyzing additional field data and using speaker playbacks to test whether rhinos perceive differences in the rhino call in the same way. White rhinos are often bred in captivity individually or only in pairs, although, unlike other rhino species, they have tendency to group. According to researchers, modified playbacks of their recordings could serve to socially stimulate such animals in the zoo. Males who hear the voices of a foreign male could thus reactivate after many years of "loneliness" and similarly the voices of unknown females could awaken their sexual activity. Unfortunately, another northern white rhinoceros, Suni, has died since the study was completed. Sudan and Angalifu thus became the last living males of an almost extinct species and at the same time its last hope.
So what does the rhino say? Are they calling? Probably for help…
Mgr. Richard Policht, Ph.D.
After experience from various zoos, he graduated from the Faculty of Science of Charles University in Prague. From 2008 he worked at the CULS at the then Institute of Tropics and Subtropics, later at the Department of Game Management and Wildlife Biology at the Faculty of Forestry and Wood Sciences. He deals with behavioural ecology and bioacoustics, his main interest is the ways of animal communication, especially the information encoded in acoustic signals and their recognition.
Prepared by: Jitka Krykorková