Growth characteristics of tusks of elephants in Kruger National Park

Two historic data sets on various tusk growth parameters were examined from African savanna elephants (Loxodonta africana) from the Kruger National Park (KNP), Republic of South Africa. Data were collected from a sample of 1,555 elephants culled randomly. In both data sets, the age and sex of the animal was known. In the first set, tusk mass, length, circumference and pulp cavity volume had also been recorded, while in the second, only tusk mass was recorded. Analysis of the data showed, as expected, significant differences between growth parameters of tusks in males and females. In males, tusks were significantly larger. Longitudinal growth in males was found to be constant throughout life, as was the expansion in circumference. Dentine was therefore deposited throughout life at an accelerating rate, resulting in accelerating mass increase in the tusks. In females, however, tusk growth apparently ceased at about 40 years of age. After this age, tusk circumference and length remained relatively constant while mass and length decreased, probably due to breakages and wear. The incidence of tusklessness and of single-tusked animals of each sex in the population was low, and the evidence suggests that the lack of tusks was mostly the result of accidental injury, not genetic inheritance. Estimates of the incidence of laterality showed that slightly more elephants were 'right-tusked' than 'left-tusked'. These results from a large sample of elephants from KNP will contribute to understanding of differences among African elephant populations and the extent to which these are genetically and/or environmentally determined.