Abstract:
Determining the age of individuals in a population can lead to a better understanding of population dynamics through age
structure analysis and estimation of age-specific fecundity and survival rates. Shoulder height has been used to accurately
assign age to free-ranging African savanna elephants. However, back length may provide an analog measurable in aerialbased
surveys. We assessed the relationship between back length and age for known-age elephants in Amboseli National
Park, Kenya, and Addo Elephant National Park, South Africa. We also compared age- and sex-specific back lengths between
these populations and compared adult female back lengths across 11 widely dispersed populations in five African countries.
Sex-specific Von Bertalanffy growth curves provided a good fit to the back length data of known-age individuals. Based on
back length, accurate ages could be assigned relatively precisely for females up to 23 years of age and males up to 17. The
female back length curve allowed more precise age assignment to older females than the curve for shoulder height does,
probably because of divergence between the respective growth curves. However, this did not appear to be the case for
males, but the sample of known-age males was limited to 27 years. Age- and sex-specific back lengths were similar in
Amboseli National Park and Addo Elephant National Park. Furthermore, while adult female back lengths in the three
Zambian populations were generally shorter than in other populations, back lengths in the remaining eight populations did
not differ significantly, in support of claims that growth patterns of African savanna elephants are similar over wide
geographic regions. Thus, the growth curves presented here should allow researchers to use aerial-based surveys to assign
ages to elephants with greater precision than previously possible and, therefore, to estimate population variables.
