Young southern white rhinos communicate using four calls tailored to different social situations, scientists have found.
Researchers studying "rhino-talk" labelled the calves' calls "whine", "snort", "threat" and "pant".
They found that the call-rate of "whines", which appeared to indicate an intention to suckle, decreased with age.
Snort, threat and pant calls were employed in different social interactions with mothers, other rhinos, and human zoo keepers.
Scientists studied a small sample of southern white rhino calves aged between one month and four years at three zoos in Germany.
One hand-reared calf produced all four calls in the same way as mother-reared calves, suggesting that the calls were mainly innate rather than learned.
Dr Sabrina Linn, from the University of Veterinary Medicine Hannover in Germany, said: "Our study provides first systematic data on vocal communication of infant and juvenile white rhinoceros and first evidence that there is a strong innate component to the development of vocal usage and production in white rhinoceros."
The findings are published in the on-line journal Public Library of Science ONE.