Determination of age and construction of population age structure of wild Asian elephants based on dung bolus circumference

Abstract

Estimating the age of wildlife is an important technique for the construction of a population age structure that could be useful for the prediction of population change. The age of wild elephants can be reliably estimated from the size of dung bolus circumference which correlates with elephant growth. This research aimed to determine a cut-off bolus circumference for the mature age class of wild Asian elephants at Salakphra Wildlife Sanctuary as inferred from the social behavior of male elephants. Males living within their natal groups were considered immature males, whereas solitary males were considered mature males. The largest bolus circumference of the immature males was used as a cut-off criterion for age class determination. Noninvasive molecular sexing was applied to determine the sex of elephant samples. From a total of 225 dung samples, 96% were successfully sex determined; 90 and 126 samples were identified as male and female, respectively. Among the male samples, 49 samples were from males living within their natal groups and 41 samples were from solitary males. The cut-off bolus circumference was determined to be 42.5 cm. The dung samples with bolus circumferences larger than the cut-off size were classified as belonging to mature elephants. The same criterion was applied to females as well. A population age structure of Salakphra elephants was created based on the bolus circumferences regardless of individual identification. The construction of population age structure based on dung sampling could be useful for a rapid population survey.