1. Angelen A, Atmadja S, Brown D, Brown J, Dutcscke M, Guariguata M, Guizol P, Kanninen M, Lubowski R, Luttrell C, Murdiyarso D, Peskett L, Seymour F, Skutsch M, Martins OS, Streck C, Verchot LV, Verweij P, Wertz-Kanounnikoff S, Wunder S (2008) Moving ahead with REDD, Center for International Forestry Research, pp 23–31. ISBN 978-979-14-1276-6
2. Alfred R, Koh PH, Lee SK, Alfred R (2010) Summarizing spatial distribution density, movement patterns and food resources to study the impacts of logging and forest conversion on Orangutans population. J Biol Sci, Sci Pub 10(2):73–83
3. Ancrenaz M, Calaque R, Lackman-Ancrenaz I (2004) Orangutan nesting behaviour in disturbed forest of Sabah, Malaysia: implications for nest census. Int J Primatol 25:983–1000
4. Ancrenaz M, Gimenez O, Ambu L, Ancrenaz K, Andau P, Goossens B, Payne J, Sawang A, Tuuga A, Lackman-Ancrenaz I (2005) Aerial surveys give new estimates for orangutans in Sabah. PLOS Biology, Malaysia, p 3
5. Buckland ST, Anderson DR, Burnham KP, Laake JL, Borchers DL, Thomas L (2001) Introduction to distance sampling, estimating abundance of biological populations, Oxford University Press, pp 67–99. ISBN: 0-19-850927-8