G. D. Winarno, R. Avenzora, S. Basuni, and M. Bismark, “The Planning of Ecotourism Opportunities Spectrum of Elephant Related Ecotourism Activities on Sumatran Elephant Home Range in Bukit Barisan Selatan National Park Province Lampung Indonesia”, IJSBAR, vol. 22, no. 2, pp. 130–148, May 2015.