Growth in the Sumatran elephant (Elephas maximus sumatranus) and age estimation based on dung diameter

Abstract

The aim of this study was to investigate age-related growth in the Sumatran elephant Elephas maximus sumatranus and to use the derived relationship to determine the age structure of the wild elephant population in Way Kambas National Park (WKNP), Sumatra. Shoulder height, forefoot circumference and diameter of dung bolus were found to be related to age of captive Sumatran elephants using the Von Bertalanffy growth function. All length measurements were highly correlated with age in the Sumatran elephant and provide growth models for determining the age structure of wild populations. Female captive elephants reached their growth plateau earlier than male elephants who continued growing throughout the ages observed. There was no clear evidence of a secondary growth spurt in male elephants. The growth model relating dung diameter to age was used to predict the age structure of the wild elephant population in WKNP from dung measured along random line transects. The wild elephant population in WKNP is young and dominated by sub-adults (between 5 and 15 years of age). There are marked differences between the age structure of the population as revealed in the current survey and that reported from previous studies, suggesting that changes have occurred within the population in the intervening period. The use of dung diameter to predict age offers a robust ®eld technique for use in situations where direct observations are limited, and the use of other age estimation methods is impractical. It is easily coupled with dung counts for estimating the size, age structure and biomass of elephant populations, and has considerable potential for investigating the effects of poaching on age structure and identifying where priority action should be directed in human±elephant con¯ict situations.

Conserving small and fragmented populations of large mammals: Non-invasive genetic sampling in an isolated population of Asian elephants in Nepal

“…2a). The resulting cut-off points between the age classes (10 cm between juveniles and sub-adults and 15 cm between sub-adults and adults) were in good concordance to bolus age-size data in wild Sumatran elephants (Reilly 2002) and in domestic elephants from Chitwan National Park in Nepal (Fig. 2b).…”

Erratum to: Elephants Also Like Coffee: Trends and Drivers of Human–Elephant Conflicts in Coffee Agroforestry Landscapes of Kodagu, Western Ghats, India

“…We grouped elephant dung piles into two age classes: juveniles and adults. Dung piles with an average bolus diameter up to 10 cm were classed as coming from juveniles (Jachmann and Bell 1984;Sukumar 1989;Reilly 2002). The age distribution obtained with this size classification was not significantly different (v 2 = 0.8622, N = 147, df = 1, P = 0.3531) from the proportions of juvenile to adult elephants in the KFD's 2005 elephant census (KFD, unpublished data).…”

Measures of dung bolus size for known‐age African elephants (Loxodonta africana): implications for age estimation

“…Comparing the accuracy of different methods is difficult because no elephant growth study has explicitly reported variance in age estimation. Reilly (2002) provided side-byside growth curves of the different methods from the same population of Sumatran elephants that suggested different growth variables may have similar variation around the lines of best fit.…”

“…In Sumatran elephants, variability between boli from the same individual is low (SD was < 4.5% and 3.3% of mean bolus size for one male and one female, respectively) (Reilly, 2002). Reilly's results add strength to our result that variability within and between dung piles for the same individual is low, even though Asian and African elephants represent different genera.…”