A note on age at sexual maturity in wild black rhinoceros

Long-range and regular observations of known-age wild mammals, which can be identified with certainty, offer a unique opportunity to obtain essential biological data from a.species. Vital population characters such as age at maturity, gestation period, calf interval, growth rate and age criteria may be determined from such a study. These characters may readily be obtained from mammals in zoological gardens. However, the artificial environment imposed by captivity presents limitations on their validity for population studies of the mammal under wholly natural conditions (Laws, 1968; Goddard, 1970). The feral black rhinoceros (Diceros bicornis (L.)) population occupying the caldera of Ngorongoro in northern Tanzania was studied over a period of almost six consecutive years. During regular observations of this population a large volume of data was collected from identified known-age rhinoceros, including several records of age at sexual maturity. These records are presented in Table 1. The population at Ngorongoro is considered to be stable (Goddard, 1967). The data presented suggest that black rhinoceros living under wild conditions attain sexual maturity at an earlier age than some specimens raised in zoological gardens (Goddard, 1967). It is possible that rhinoceros 3 and 4 may have mated at an earlier date; in these cases sexual maturity may have been attained at a younger age. TABLE 1 No. Sex Birthday Age at sexual Remarks maturity (y) 1 F 1961 4.7-5.7* Produced female calf Dec. 1967 2 F 1961 3.8-5.0* Produced male calf Jan.-March l967 3 M Oct. 1962 4.3 Mating 17.2.67 4 F Aug. 1963 4.5 Mating 3.2.68; Produced male calf June 1969 * Assuming a gestation period of 15-18 months (Goddard, 1967)