Kongrit, C., and C. Siripunkaw. “Determination of Age and Construction of Population Age Structure of Wild Asian Elephants Based on Dung Bolus Circumference”. The Thai Journal of Veterinary Medicine, vol. 47, no. 2, June 2017, pp. 145-53, https://he01.tci-thaijo.org/index.php/tjvm/article/view/90293.