Characteristics of the animals included in the study.

1Age at time of call recordings. A = adult, S = subadult. The animals were classified by age class following Owen-Smith [10], [11]; females were regarded as adults at 6.5–7 years of age and males between 10 and 12 years of age. 2I = visual isolation from other rhinos, PI = partial isolation: the animal was visually isolated from the rest of its group, but was in the company of other rhinos, VC = in visual contact with group member(s).